MFS Series Trust IX (IAB) NCSRS

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number 811-02464

MFS SERIES TRUST IX

(Exact name of registrant as specified in charter)

111 Huntington Avenue, Boston, Massachusetts 02199 (Address of principal executive offices) (Zip code)

Christopher R. Bohane

Massachusetts Financial Services Company

111Huntington Avenue Boston, Massachusetts 02199

(Name and address of agents for service)

Registrant's telephone number, including area code: (617) 954-5000

Date of fiscal year end: October 31*

Date of reporting period: April 30, 2023

*This Form N-CSR pertains to the following series of the Registrant: MFS Inflation-Adjusted Bond Fund. The remaining series of the Registrant have fiscal year ends of April 30.

Table of Contents

Portfolio Composition

Portfolio structure (i)

Fixed income sectors (i)

U.S. Treasury Securities	100.5%
Commercial Mortgage-Backed Securities	1.3%
Municipal Bonds	1.3%
Mortgage-Backed Securities	0.7%
Investment Grade Corporates	0.6%
Collateralized Debt Obligations	0.2%

Composition including fixed income credit quality (a)(i)

AAA	1.4%
AA	0.9%
A	0.8%
BBB	0.3%
U.S. Government	95.8%
Federal Agencies	0.7%
Not rated	4.7%
Cash & Cash Equivalents	0.1%
Other	(4.7)%

Portfolio facts

Average Duration (d)	7.6
Average Effective Maturity (m)	7.7 yrs.

(a)

For all securities other than those specifically described below, ratings are assigned to underlying securities utilizing ratings from Moody’s, Fitch, and Standard & Poor’s rating agencies and applying the following hierarchy: If all three agencies provide a rating, the middle rating (after dropping the highest and lowest ratings) is assigned; if two of the three agencies rate a security, the lower of the two is assigned. If none of the 3 rating agencies above assign a rating, but the security is rated by DBRS Morningstar, then the DBRS Morningstar rating is assigned. If none of the 4 rating agencies listed above rate the security, but the security is rated by the Kroll Bond Rating Agency (KBRA), then the KBRA rating is assigned. Ratings are shown in the S&P and Fitch scale (e.g., AAA). Securities rated BBB or higher are considered investment grade. All ratings are subject to change. U.S. Government includes securities issued by the U.S. Department of the Treasury. Federal Agencies includes rated and unrated U.S. Agency fixed-income securities, U.S. Agency mortgage-backed securities, and collateralized mortgage obligations of U.S. Agency mortgage-backed securities.

Not Rated includes fixed income securities and fixed income derivatives that have not been rated by any rating agency. The fund may or may not have held all of these instruments on this date. The fund is not rated by these agencies.

(d)

Duration is a measure of how much a bond’s price is likely to fluctuate with general changes in interest rates, e.g., if rates rise 1.00%, a bond with a 5-year duration is likely to lose about 5.00% of its value due to the interest rate move. The Average Duration calculation reflects the impact of the equivalent exposure of derivative positions, if any.

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Portfolio Composition - continued

(i)

For purposes of this presentation, the components include the value of securities, and reflect the impact of the equivalent exposure of derivative positions, if any. These amounts may be negative from time to time. Equivalent exposure is a calculated amount that translates the derivative position into a reasonable approximation of the amount of the underlying asset that the portfolio would have to hold at a given point in time to have the same price sensitivity that results from the portfolio’s ownership of the derivative contract. When dealing with derivatives, equivalent exposure is a more representative measure of the potential impact of a position on portfolio performance than value. The bond component will include any accrued interest amounts.

(m)

In determining each instrument’s effective maturity for purposes of calculating the fund’s dollar-weighted average effective maturity, MFS uses the instrument’s stated maturity or, if applicable, an earlier date on which MFS believes it is probable that a maturity-shortening device (such as a put, pre-refunding or prepayment) will cause the instrument to be repaid. Such an earlier date can be substantially shorter than the instrument’s stated maturity.

Where the fund holds convertible bonds, they are treated as part of the equity portion of the portfolio.

Cash & Cash Equivalents includes any cash, investments in money market funds, short-term securities, and other assets less liabilities. Please see the Statement of Assets and Liabilities for additional information related to the fund’s cash position and other assets and liabilities.

Other includes equivalent exposure from currency derivatives and/or any offsets to derivative positions and may be negative.

Percentages are based on net assets as of April 30, 2023.

The portfolio is actively managed and current holdings may be different.

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Expense Table

Fund expenses borne by the shareholders during the period,
November 1, 2022 through April 30, 2023

As a shareholder of the fund, you incur two types of costs: (1) transaction costs, including sales charges (loads) on certain purchase or redemption payments, and (2) ongoing costs, including management fees; distribution and service (12b-1) fees; and other fund expenses. This example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds.

The example is based on an investment of $1,000 invested at the beginning of the period and held for the entire period November 1, 2022 through April 30, 2023.

Actual Expenses

The first line for each share class in the following table provides information about actual account values and actual expenses. You may use the information in this line, together with the amount you invested, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number in the first line under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes

The second line for each share class in the following table provides information about hypothetical account values and hypothetical expenses based on the fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses, which is not the fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as sales charges (loads). Therefore, the second line for each share class in the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would have been higher.

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Expense Table - continued

Share Class		Annualized Expense Ratio	Beginning Account Value 11/01/22	Ending Account Value 4/30/23	Expenses Paid During Period (p) 11/01/22-4/30/23
A	Actual	0.64%	$1,000.00	$1,041.41	$3.24
A	Hypothetical (h)	0.64%	$1,000.00	$1,021.62	$3.21
B	Actual	1.39%	$1,000.00	$1,038.19	$7.02
B	Hypothetical (h)	1.39%	$1,000.00	$1,017.90	$6.95
C	Actual	1.49%	$1,000.00	$1,036.79	$7.52
C	Hypothetical (h)	1.49%	$1,000.00	$1,017.41	$7.45
I	Actual	0.49%	$1,000.00	$1,043.23	$2.48
I	Hypothetical (h)	0.49%	$1,000.00	$1,022.36	$2.46
R1	Actual	1.49%	$1,000.00	$1,037.08	$7.53
R1	Hypothetical (h)	1.49%	$1,000.00	$1,017.41	$7.45
R2	Actual	0.99%	$1,000.00	$1,039.79	$5.01
R2	Hypothetical (h)	0.99%	$1,000.00	$1,019.89	$4.96
R3	Actual	0.74%	$1,000.00	$1,041.69	$3.75
R3	Hypothetical (h)	0.74%	$1,000.00	$1,021.12	$3.71
R4	Actual	0.49%	$1,000.00	$1,042.20	$2.48
R4	Hypothetical (h)	0.49%	$1,000.00	$1,022.36	$2.46
R6	Actual	0.42%	$1,000.00	$1,042.43	$2.13
R6	Hypothetical (h)	0.42%	$1,000.00	$1,022.71	$2.11

(h)	5% class return per year before expenses.

(p)

“Expenses Paid During Period” are equal to each class’s annualized expense ratio, as shown above, multiplied by the average account value over the period, multiplied by 181/365 (to reflect the one-half year period). Expenses paid do not include any applicable sales charges (loads). If these transaction costs had been included, your costs would have been higher.

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Portfolio of Investments

4/30/23 (unaudited)

The Portfolio of Investments is a complete list of all securities owned by your fund. It is categorized by broad-based asset classes.

Issuer		Shares/Par	Value ($)
Bonds – 99.7%
Asset-Backed & Securitized – 1.5%
3650R Commercial Mortgage Trust, 2021-PF1, “XA”, 1.137%, 11/15/2054 (i)	$	14,711,547	$798,896
AREIT 2022-CRE6 Trust, “AS”, FLR, 6.408% (SOFR - 30 day + 1.65%), 1/16/2037 (n)		2,462,500	2,361,688
BBCMS Mortgage Trust, 2021-C10, “XA”, 1.417%, 7/15/2054 (i)		13,285,029	903,842
BBCMS Mortgage Trust, 2021-C9, “XA”, 1.744%, 2/15/2054 (i)		8,070,501	721,500
Benchmark 2021-B23 Mortgage Trust, “XA”, 1.376%, 2/15/2054 (i)		25,430,138	1,709,724
Benchmark 2021-B24 Mortgage Trust, “XA”, 1.268%, 3/15/2054 (i)		15,468,635	942,734
Benchmark 2021-B27 Mortgage Trust, “XA”, 1.381%, 7/15/2054 (i)		20,976,534	1,503,176
Benchmark 2021-B28 Mortgage Trust, “XA”, 1.392%, 8/15/2054 (i)		25,382,722	1,838,245
BSPDF 2021-FL1 Issuer Ltd., “AS”, FLR, 6.427% (LIBOR - 1mo. + 1.48%), 10/15/2036 (n)		3,056,500	2,836,881
Commercial Mortgage Pass-Through Certificates, 2021-BN31, “XA”, 1.428%, 2/15/2054 (i)		19,490,768	1,446,314
Morgan Stanley Capital I Trust, 2021-L5, “XA”, 1.417%, 5/15/2054 (i)		10,257,312	696,026
Morgan Stanley Capital I Trust, 2021-L6, “XA”, 1.34%, 6/15/2054 (i)		12,902,645	801,880
Morgan Stanley Capital I Trust, 2021-L7, “XA”, 1.212%, 10/15/2054 (i)		27,564,999	1,614,758
PFP III 2021-8 Ltd., “AS”, FLR, 6.196% (LIBOR - 1mo. + 1.25%), 8/09/2037 (n)		3,622,500	3,417,745
Wells Fargo Commercial Mortgage Trust, 2021-C60, “XA”, 1.658%, 8/15/2054 (i)		9,431,917	780,436
			$22,373,845
Consumer Services – 0.1%
Conservation Fund, 3.474%, 12/15/2029	$	1,438,000	$1,246,334
Industrial Revenue - Other – 0.0%
Howard University, Washington D.C., AGM, 2.416%, 10/01/2024	$	325,000	$314,426
Howard University, Washington D.C., AGM, 2.516%, 10/01/2025		402,000	380,995
			$695,421

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Portfolio of Investments (unaudited) – continued

Issuer		Shares/Par	Value ($)
Bonds – continued
Medical & Health Technology & Services – 0.2%
ProMedica Toledo Hospital, “B”, AGM, 5.325%, 11/15/2028	$	2,421,000	$2,428,786
ProMedica Toledo Hospital, “B”, AGM, 5.75%, 11/15/2038		747,000	729,209
			$3,157,995
Mortgage-Backed – 0.6%
Freddie Mac, 1.916%, 4/25/2030 (i)	$	3,519,182	$368,717
Freddie Mac, 1.768%, 5/25/2030 (i)		6,326,494	616,436
Freddie Mac, 1.263%, 9/25/2030 (i)		3,529,812	252,585
Freddie Mac, 0.42%, 1/25/2031 (i)		29,795,319	583,497
Freddie Mac, 0.872%, 1/25/2031 (i)		11,388,256	576,409
Freddie Mac, 1.026%, 1/25/2031 (i)		8,529,316	507,954
Freddie Mac, 0.612%, 3/25/2031 (i)		36,402,283	1,161,761
Freddie Mac, 1.325%, 5/25/2031 (i)		4,421,663	351,304
Freddie Mac, 1.039%, 7/25/2031 (i)		7,521,262	475,730
Freddie Mac, 0.632%, 9/25/2031 (i)		32,486,236	1,140,124
Freddie Mac, 0.955%, 9/25/2031 (i)		9,783,880	566,822
Freddie Mac, 0.441%, 11/25/2031 (i)		49,721,062	1,262,671
Freddie Mac, 0.597%, 12/25/2031 (i)		50,485,813	1,768,033
Freddie Mac, 0.665%, 12/25/2031 (i)		8,215,224	323,129
			$9,955,172
Municipals – 1.3%
California Earthquake Authority Rev., Taxable, “B”, 1.477%, 7/01/2023	$	1,310,000	$1,301,345
Chicago, IL, Transit Authority Sales Tax Receipts Refunding Rev., Taxable, “B”, 2.064%, 12/01/2024		523,000	500,016
Chicago, IL, Transit Authority Sales Tax Receipts Refunding Rev., Taxable, “B”, 2.214%, 12/01/2025		392,000	369,016
Colorado Health Facilities Authority Rev., Taxable (Covenant Living Communities and Services), “B”, 2.8%, 12/01/2026		825,000	778,892
Golden State, CA, Tobacco Securitization Corp., Tobacco Settlement Rev., Taxable, “B”, 3%, 6/01/2046		2,690,000	2,493,664
Massachusetts Educational Financing Authority, Education Loan Rev., Taxable, “M-A”, 2.641%, 7/01/2037		7,720,000	7,110,558
Michigan Finance Authority Student Loan Asset-Backed Rev., Taxable, “A-1A”, 1.3%, 7/25/2061		2,528,997	2,371,654
Michigan Finance Authority Tobacco Settlement Asset-Backed Rev., Taxable (2006 Sold Tobacco Receipts), “A-1”, 2.326%, 6/01/2030		619,743	593,321
New Jersey Turnpike Authority, Turnpike Rev., Taxable, “B”, 1.047%, 1/01/2026		745,000	680,732
Philadelphia, PA, School District, Taxable, “A”, AGM, 5.995%, 9/01/2030		1,925,000	2,091,455

Table of Contents

Portfolio of Investments (unaudited) – continued

Issuer		Shares/Par	Value ($)
Bonds – continued
Municipals – continued
West Virginia Tobacco Settlement Financing Authority Asset-Backed Refunding, Taxable, “A-1”, 1.497%, 6/01/2024	$	1,020,000	$976,250
West Virginia Tobacco Settlement Financing Authority Asset-Backed Refunding, Taxable, “A-1”, 1.647%, 6/01/2025		835,000	777,170
			$20,044,073
U.S. Treasury Inflation Protected Securities – 95.7%
U.S. Treasury Bonds, 2.375%, 1/15/2025	$	21,354,480	$21,481,550
U.S. Treasury Bonds, 2%, 1/15/2026		82,770,014	83,614,689
U.S. Treasury Bonds, 1.75%, 1/15/2028		17,787,856	18,146,045
U.S. Treasury Bonds, 3.625%, 4/15/2028		52,562,305	58,397,029
U.S. Treasury Bonds, 0.75%, 2/15/2042		106,020,452	91,685,948
U.S. Treasury Bonds, 0.625%, 2/15/2043		36,791,376	30,815,292
U.S. Treasury Bonds, 0.75%, 2/15/2045		54,246,051	45,819,901
U.S. Treasury Bonds, 1%, 2/15/2048		20,971,284	18,441,828
U.S. Treasury Bonds, 0.25%, 2/15/2050		10,719,510	7,672,301
U.S. Treasury Bonds, 0.125%, 2/15/2051		16,362,022	11,176,667
U.S. Treasury Bonds, 0.125%, 2/15/2052		57,493,240	39,191,412
U.S. Treasury Notes, 0.25%, 1/15/2025 (f)		181,693,687	176,358,801
U.S. Treasury Notes, 0.625%, 1/15/2026		130,120,895	126,838,647
U.S. Treasury Notes, 0.375%, 1/15/2027		78,333,798	75,374,861
U.S. Treasury Notes, 0.375%, 7/15/2027		86,994,485	83,880,014
U.S. Treasury Notes, 0.5%, 1/15/2028		68,385,874	65,884,625
U.S. Treasury Notes, 0.875%, 1/15/2029		166,047,216	162,453,852
U.S. Treasury Notes, 0.125%, 7/15/2030		117,365,334	108,671,436
U.S. Treasury Notes, 0.125%, 1/15/2031		138,569,456	127,368,425
U.S. Treasury Notes, 0.125%, 1/15/2032		138,598,204	125,987,212
			$1,479,260,535
Utilities - Electric Power – 0.3%
Pacific Gas & Electric Co., 3.25%, 2/16/2024	$	4,253,000	$4,163,160
Total Bonds (Identified Cost, $1,647,199,368)			$1,540,896,535
Investment Companies (h) – 0.1%
Money Market Funds – 0.1%
MFS Institutional Money Market Portfolio, 4.59% (v) (Identified Cost, $2,421,842)		2,421,702	$2,422,187


Other Assets, Less Liabilities – 0.2%			2,835,400
Net Assets – 100.0%			$1,546,154,122

(f)

All or a portion of the security has been segregated as collateral for open futures contracts.

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Portfolio of Investments (unaudited) – continued

(h)	An affiliated issuer, which may be considered one in which the fund owns 5% or more of the outstanding voting securities, or a company which is under common control. At period end, the aggregate values of the fund's investments in affiliated issuers and in unaffiliated issuers were $2,422,187 and $1,540,896,535, respectively.
(i)	Interest only security for which the fund receives interest on notional principal (Par amount). Par amount shown is the notional principal and does not reflect the cost of the security.
(n)	Securities exempt from registration under Rule 144A of the Securities Act of 1933. These securities may be sold in the ordinary course of business in transactions exempt from registration, normally to qualified institutional buyers. At period end, the aggregate value of these securities was $8,616,314, representing 0.6% of net assets.
(v)	Affiliated issuer that is available only to investment companies managed by MFS. The rate quoted for the MFS Institutional Money Market Portfolio is the annualized seven-day yield of the fund at period end.

The following abbreviations are used in this report and are defined:
AGM	Assured Guaranty Municipal
FLR	Floating Rate. Interest rate resets periodically based on the parenthetically disclosed reference rate plus a spread (if any). The period-end rate reported may not be the current rate. All reference rates are USD unless otherwise noted.
LIBOR	London Interbank Offered Rate
SOFR	Secured Overnight Financing Rate

Derivative Contracts at 4/30/23

Futures Contracts
Description	Long/ Short	Currency	Contracts	Notional Amount	Expiration Date	Value/Unrealized Appreciation (Depreciation)
Asset Derivatives
Interest Rate Futures
U.S. Treasury Note 2 yr	Short	USD	786	$162,044,953	June – 2023	$326,823
U.S. Treasury Ultra Bond	Short	USD	162	22,907,812	June – 2023	85,131
						$411,954
Liability Derivatives
Interest Rate Futures
U.S. Treasury Note 10 yr	Long	USD	1,008	$116,124,750	June – 2023	$(40,781)
U.S. Treasury Note 5 yr	Long	USD	1,296	142,225,876	June – 2023	(305,582)
						$(346,363)

At April 30, 2023, the fund had liquid securities with an aggregate value of $3,670,094 to cover any collateral or margin obligations for certain derivative contracts.

See Notes to Financial Statements

Table of Contents

Financial Statements

Statement of Assets and Liabilities

At 4/30/23 (unaudited)

This statement represents your fund’s balance sheet, which details the assets and liabilities comprising the total value of the fund.

Assets
Investments in unaffiliated issuers, at value (identified cost, $1,647,199,368)	$1,540,896,535
Investments in affiliated issuers, at value (identified cost, $2,421,842)	2,422,187
Receivables for
Net daily variation margin on open futures contracts	362,269
Investments sold	2,466,341
Fund shares sold	907,498
Interest	3,093,000
Other assets	9,902
Total assets	$1,550,157,732
Liabilities
Payables for
Investments purchased	$3,108,499
Fund shares reacquired	673,481
Payable to affiliates
Investment adviser	62,638
Administrative services fee	2,537
Shareholder servicing costs	41,583
Distribution and service fees	2,395
Payable for independent Trustees' compensation	3,907
Accrued expenses and other liabilities	108,570
Total liabilities	$4,003,610
Net assets	$1,546,154,122
Net assets consist of
Paid-in capital	$1,734,213,892
Total distributable earnings (loss)	(188,059,770)
Net assets	$1,546,154,122
Shares of beneficial interest outstanding	161,761,183

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Financial Statements

Statement of Operations

Six months ended 4/30/23 (unaudited)

This statement describes how much your fund earned in investment income and accrued in expenses. It also describes any gains and/or losses generated by fund operations.

Net investment income (loss)
Income
Interest	$27,937,569
Dividends from affiliated issuers	125,642
Total investment income	$28,063,211
Expenses
Management fee	$3,396,407
Distribution and service fees	171,541
Shareholder servicing costs	76,732
Administrative services fee	116,684
Independent Trustees' compensation	13,251
Custodian fee	47,859
Shareholder communications	12,030
Audit and tax fees	26,698
Legal fees	3,652
Miscellaneous	112,506
Total expenses	$3,977,360
Reduction of expenses by investment adviser and distributor	(649,869)
Net expenses	$3,327,491
Net investment income (loss)	$24,735,720
Realized and unrealized gain (loss)
Realized gain (loss) (identified cost basis)
Unaffiliated issuers	$(30,967,797)
Affiliated issuers	(13,038)
Futures contracts	(1,233,288)
Net realized gain (loss)	$(32,214,123)
Change in unrealized appreciation or depreciation
Unaffiliated issuers	$71,081,287
Affiliated issuers	350
Futures contracts	65,591
Net unrealized gain (loss)	$71,147,228
Net realized and unrealized gain (loss)	$38,933,105
Change in net assets from operations	$63,668,825

See Notes to Financial Statements

Table of Contents

Financial Statements

Financial Highlights

The financial highlights table is intended to help you understand the fund's financial performance for the semiannual period and the past 5 fiscal years. Certain information reflects financial results for a single fund share. The total returns in the table represent the rate that an investor would have earned (or lost) on an investment in the fund share class (assuming reinvestment of all distributions) held for the entire period.

Class A	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.36	$11.46	$11.20	$10.46	$9.83	$10.32
Income (loss) from investment operations
Net investment income (loss) (d)	$0.14	$0.63	$0.40	$0.12	$0.17	$0.25
Net realized and unrealized gain (loss)	0.24	(1.92)	0.21	0.75	0.69	(0.46)
Total from investment operations	$0.38	$(1.29)	$0.61	$0.87	$0.86	$(0.21)
Less distributions declared to shareholders
From net investment income	$(0.22)	$(0.81)	$(0.35)	$(0.13)	$(0.23)	$(0.28)
Net asset value, end of period (x)	$9.52	$9.36	$11.46	$11.20	$10.46	$9.83
Total return (%) (r)(s)(t)(x)	4.14(n)	(11.79)	5.48	8.42	8.80	(2.07)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	0.82(a)	0.81	0.87	0.93	0.95	0.96
Expenses after expense reductions	0.64(a)	0.64	0.66	0.76	0.80	0.80
Net investment income (loss)	3.00(a)(l)	6.02	3.55	1.11	1.69	2.44
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$104,106	$117,619	$114,091	$65,862	$46,796	$44,085

See Notes to Financial Statements

Table of Contents

Financial Highlights – continued

Class B	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.29	$11.37	$11.13	$10.42	$9.79	$10.27
Income (loss) from investment operations
Net investment income (loss) (d)	$0.10	$0.54	$0.28	$0.02	$0.09	$0.17
Net realized and unrealized gain (loss)	0.25	(1.90)	0.23	0.77	0.69	(0.44)
Total from investment operations	$0.35	$(1.36)	$0.51	$0.79	$0.78	$(0.27)
Less distributions declared to shareholders
From net investment income	$(0.19)	$(0.72)	$(0.27)	$(0.08)	$(0.15)	$(0.21)
Net asset value, end of period (x)	$9.45	$9.29	$11.37	$11.13	$10.42	$9.79
Total return (%) (r)(s)(t)(x)	3.82(n)	(12.47)	4.62	7.65	8.03	(2.72)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	1.57(a)	1.56	1.62	1.69	1.70	1.71
Expenses after expense reductions	1.39(a)	1.38	1.41	1.53	1.55	1.55
Net investment income (loss)	2.10(a)(l)	5.12	2.51	0.21	0.91	1.73
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$424	$568	$1,085	$1,454	$3,404	$4,774

Class C	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.28	$11.37	$11.13	$10.42	$9.79	$10.28
Income (loss) from investment operations
Net investment income (loss) (d)	$0.10	$0.54	$0.28	$0.02	$0.08	$0.16
Net realized and unrealized gain (loss)	0.24	(1.91)	0.22	0.77	0.69	(0.45)
Total from investment operations	$0.34	$(1.37)	$0.50	$0.79	$0.77	$(0.29)
Less distributions declared to shareholders
From net investment income	$(0.19)	$(0.72)	$(0.26)	$(0.08)	$(0.14)	$(0.20)
Net asset value, end of period (x)	$9.43	$9.28	$11.37	$11.13	$10.42	$9.79
Total return (%) (r)(s)(t)(x)	3.68(n)	(12.54)	4.52	7.58	7.92	(2.91)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	1.57(a)	1.56	1.62	1.68	1.70	1.71
Expenses after expense reductions	1.49(a)	1.49	1.51	1.62	1.65	1.65
Net investment income (loss)	2.08(a)(l)	5.19	2.50	0.17	0.76	1.61
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$4,387	$5,412	$6,115	$4,771	$5,374	$7,185

See Notes to Financial Statements

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Financial Highlights – continued

Class I	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.37	$11.48	$11.22	$10.47	$9.84	$10.33
Income (loss) from investment operations
Net investment income (loss) (d)	$0.15	$0.68	$0.46	$0.15	$0.17	$0.27
Net realized and unrealized gain (loss)	0.24	(1.97)	0.16(g)	0.74	0.70	(0.46)
Total from investment operations	$0.39	$(1.29)	$0.62	$0.89	$0.87	$(0.19)
Less distributions declared to shareholders
From net investment income	$(0.23)	$(0.82)	$(0.36)	$(0.14)	$(0.24)	$(0.30)
Net asset value, end of period (x)	$9.53	$9.37	$11.48	$11.22	$10.47	$9.84
Total return (%) (r)(s)(t)(x)	4.21(n)	(11.73)	5.60	8.61	8.96	(1.91)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	0.57(a)	0.56	0.62	0.68	0.70	0.70
Expenses after expense reductions	0.49(a)	0.49	0.51	0.61	0.65	0.65
Net investment income (loss)	3.12(a)(l)	6.48	4.03	1.34	1.72	2.69
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$28,071	$22,796	$13,708	$5,633	$4,503	$5,332

Class R1	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.25	$11.34	$11.10	$10.41	$9.78	$10.26
Income (loss) from investment operations
Net investment income (loss) (d)	$0.10	$0.53	$0.29	$0.02	$0.09	$0.17
Net realized and unrealized gain (loss)	0.24	(1.90)	0.21	0.75	0.68	(0.45)
Total from investment operations	$0.34	$(1.37)	$0.50	$0.77	$0.77	$(0.28)
Less distributions declared to shareholders
From net investment income	$(0.19)	$(0.72)	$(0.26)	$(0.08)	$(0.14)	$(0.20)
Net asset value, end of period (x)	$9.40	$9.25	$11.34	$11.10	$10.41	$9.78
Total return (%) (r)(s)(t)(x)	3.71(n)	(12.55)	4.55	7.40	7.93	(2.82)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	1.57(a)	1.56	1.62	1.68	1.70	1.71
Expenses after expense reductions	1.49(a)	1.49	1.51	1.61	1.65	1.65
Net investment income (loss)	2.22(a)(l)	5.08	2.56	0.20	0.86	1.68
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$917	$874	$837	$454	$332	$305

See Notes to Financial Statements

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Financial Highlights – continued

Class R2	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.33	$11.43	$11.18	$10.45	$9.82	$10.30
Income (loss) from investment operations
Net investment income (loss) (d)	$0.12	$0.57	$0.35	$0.08	$0.14	$0.21
Net realized and unrealized gain (loss)	0.25	(1.90)	0.21	0.76	0.68	(0.44)
Total from investment operations	$0.37	$(1.33)	$0.56	$0.84	$0.82	$(0.23)
Less distributions declared to shareholders
From net investment income	$(0.21)	$(0.77)	$(0.31)	$(0.11)	$(0.19)	$(0.25)
Net asset value, end of period (x)	$9.49	$9.33	$11.43	$11.18	$10.45	$9.82
Total return (%) (r)(s)(t)(x)	3.98(n)	(12.15)	5.07	8.08	8.43	(2.32)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	1.07(a)	1.06	1.12	1.18	1.20	1.21
Expenses after expense reductions	0.99(a)	0.99	1.01	1.11	1.15	1.15
Net investment income (loss)	2.63(a)(l)	5.46	3.11	0.71	1.34	2.09
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$542	$589	$686	$586	$643	$603

Class R3	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.35	$11.45	$11.20	$10.46	$9.83	$10.32
Income (loss) from investment operations
Net investment income (loss) (d)	$0.11	$0.62	$0.37	$0.10	$0.16	$0.24
Net realized and unrealized gain (loss)	0.28	(1.92)	0.22	0.76	0.69	(0.46)
Total from investment operations	$0.39	$(1.30)	$0.59	$0.86	$0.85	$(0.22)
Less distributions declared to shareholders
From net investment income	$(0.22)	$(0.80)	$(0.34)	$(0.12)	$(0.22)	$(0.27)
Net asset value, end of period (x)	$9.52	$9.35	$11.45	$11.20	$10.46	$9.83
Total return (%) (r)(s)(t)(x)	4.17(n)	(11.90)	5.30	8.35	8.70	(2.16)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	0.82(a)	0.81	0.87	0.93	0.95	0.96
Expenses after expense reductions	0.74(a)	0.74	0.76	0.86	0.90	0.90
Net investment income (loss)	2.33(a)(l)	5.83	3.25	0.96	1.57	2.36
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$872	$1,516	$2,128	$1,609	$1,590	$1,873

See Notes to Financial Statements

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Financial Highlights – continued

Class R4	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.36	$11.46	$11.20	$10.45	$9.83	$10.32
Income (loss) from investment operations
Net investment income (loss) (d)	$0.15	$0.63	$0.42	$0.13	$0.16	$0.27
Net realized and unrealized gain (loss)	0.24	(1.91)	0.20	0.76	0.70	(0.46)
Total from investment operations	$0.39	$(1.28)	$0.62	$0.89	$0.86	$(0.19)
Less distributions declared to shareholders
From net investment income	$(0.23)	$(0.82)	$(0.36)	$(0.14)	$(0.24)	$(0.30)
Net asset value, end of period (x)	$9.52	$9.36	$11.46	$11.20	$10.45	$9.83
Total return (%) (r)(s)(t)(x)	4.22(n)	(11.66)	5.60	8.63	8.86	(1.92)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	0.57(a)	0.56	0.62	0.68	0.70	0.72
Expenses after expense reductions	0.49(a)	0.48	0.51	0.62	0.65	0.65
Net investment income (loss)	3.23(a)(l)	6.00	3.68	1.22	1.58	2.60
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$90	$84	$91	$87	$90	$140

Class R6	_{Six months} _ended	Year ended
	4/30/23 (unaudited)	10/31/22	10/31/21	10/31/20	10/31/19	10/31/18
Net asset value, beginning of period	$9.40	$11.51	$11.24	$10.49	$9.86	$10.35
Income (loss) from investment operations
Net investment income (loss) (d)	$0.15	$0.64	$0.42	$0.15	$0.20	$0.27
Net realized and unrealized gain (loss)	0.24	(1.92)	0.22	0.75	0.68	(0.45)
Total from investment operations	$0.39	$(1.28)	$0.64	$0.90	$0.88	$(0.18)
Less distributions declared to shareholders
From net investment income	$(0.23)	$(0.83)	$(0.37)	$(0.15)	$(0.25)	$(0.31)
Net asset value, end of period (x)	$9.56	$9.40	$11.51	$11.24	$10.49	$9.86
Total return (%) (r)(s)(t)(x)	4.24(n)	(11.62)	5.74	8.66	9.03	(1.82)
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions	0.49(a)	0.48	0.55	0.60	0.62	0.62
Expenses after expense reductions	0.42(a)	0.41	0.44	0.53	0.57	0.57
Net investment income (loss)	3.29(a)(l)	6.07	3.71	1.34	1.95	2.68
Portfolio turnover	20(n)	86	57	36	38	23
Net assets at end of period (000 omitted)	$1,406,745	$1,355,560	$1,622,398	$1,281,030	$1,150,953	$1,108,604

See Notes to Financial Statements

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Financial Highlights – continued

(a)	Annualized.
(d)	Per share data is based on average shares outstanding.
(g)	The per share amount varies from the net investment income and/or net realized and unrealized gain/loss for the period because of the timing of sales of fund shares and the per share amounts of realized and unrealized gains and losses and/or inflation/deflation adjustments at such time.
(l)	Recognition of net investment income by the fund may be affected by inflation/deflation adjustments through period end and the actual annual net investment income ratio may differ.
(n)	Not annualized.
(r)	Certain expenses have been reduced without which performance would have been lower.
(s)	From time to time the fund may receive proceeds from litigation settlements, without which performance would be lower.
(t)	Total returns do not include any applicable sales charges.
(x)	The net asset values and total returns have been calculated on net assets which include adjustments made in accordance with U.S. generally accepted accounting principles required at period end for financial reporting purposes.

See Notes to Financial Statements

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Notes to Financial Statements

(unaudited)

(1) Business and Organization

MFS Inflation-Adjusted Bond Fund (the fund) is a diversified series of MFS Series Trust IX (the trust). The trust is organized as a Massachusetts business trust and is registered under the Investment Company Act of 1940, as amended, as an open-end management investment company.

The fund is an investment company and accordingly follows the investment company accounting and reporting guidance of the Financial Accounting Standards Board (FASB) Accounting Standards Codification Topic 946 Financial Services - Investment Companies.

(2) Significant Accounting Policies

General — The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of increases and decreases in net assets from operations during the reporting period. Actual results could differ from those estimates. In the preparation of these financial statements, management has evaluated subsequent events occurring after the date of the fund’s Statement of Assets and Liabilities through the date that the financial statements were issued.

Balance Sheet Offsetting — The fund's accounting policy with respect to balance sheet offsetting is that, absent an event of default by the counterparty or a termination of the agreement, the International Swaps and Derivatives Association (ISDA) Master Agreement, or similar agreement, does not result in an offset of reported amounts of financial assets and financial liabilities in the Statement of Assets and Liabilities across transactions between the fund and the applicable counterparty. The fund's right to setoff may be restricted or prohibited by the bankruptcy or insolvency laws of the particular jurisdiction to which a specific master netting agreement counterparty is subject. Balance sheet offsetting disclosures, to the extent applicable to the fund, have been included in the fund’s Significant Accounting Policies note under the captions for each of the fund’s in-scope financial instruments and transactions.

Investment Valuations — Subject to its oversight, the fund's Board of Trustees has delegated primary responsibility for determining or causing to be determined the value of the fund’s investments to MFS as the fund's adviser, pursuant to the fund’s valuation policy and procedures which have been adopted by the adviser and approved by the Board. In accordance with Rule 2a-5 under the Investment Company Act of 1940, the Board of Trustees designated the adviser as the “valuation designee” of the fund. If the adviser, as valuation designee, determines that reliable market quotations are not readily available for an investment, the investment is valued at fair value as determined in good faith by the adviser in accordance with the adviser’s fair valuation policy and procedures.

Under the fund's valuation policy and procedures, debt instruments and floating rate loans, including restricted debt instruments, are generally valued at an evaluated or composite bid as provided by a third-party pricing service. Short-term instruments with a maturity at issuance of 60 days or less may be valued at amortized cost, which approximates market value. Futures contracts are generally valued at last posted

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Notes to Financial Statements (unaudited) - continued

settlement price on their primary exchange as provided by a third-party pricing service. Futures contracts for which there were no trades that day for a particular position are generally valued at the closing bid quotation on their primary exchange as provided by a third-party pricing service. Open-end investment companies are generally valued at net asset value per share. The values of foreign securities and other assets and liabilities expressed in foreign currencies are converted to U.S. dollars using the mean of bid and asked prices for rates provided by a third-party pricing service.

Under the fund’s valuation policy and procedures, market quotations are not considered to be readily available for debt instruments, floating rate loans, and many types of derivatives. These investments are generally valued at fair value based on information from third-party pricing services or otherwise determined by the adviser in accordance with the adviser’s fair valuation policy and procedures. Securities and other assets generally valued on the basis of information from a third-party pricing service may also be valued at a broker/dealer bid quotation. In determining values, third-party pricing services can utilize both transaction data and market information such as yield, quality, coupon rate, maturity, type of issue, trading characteristics, spreads and other market data. An investment may also be valued at fair value if the adviser determines that the investment’s value has been materially affected by events occurring after the close of the exchange or market on which the investment is principally traded (such as foreign exchange or market) and prior to the determination of the fund’s net asset value, or after the halt of trading of a specific security where trading does not resume prior to the close of the exchange or market on which the security is principally traded. The adviser generally relies on third-party pricing services or other information (such as the correlation with price movements of similar securities in the same or other markets; the type, cost and investment characteristics of the security; the business and financial condition of the issuer; and trading and other market data) to assist in determining whether to fair value and at what value to fair value an investment. The value of an investment for purposes of calculating the fund’s net asset value can differ depending on the source and method used to determine value. When fair valuation is used, the value of an investment used to determine the fund’s net asset value may differ from quoted or published prices for the same investment. There can be no assurance that the fund could obtain the fair value assigned to an investment if it were to sell the investment at the same time at which the fund determines its net asset value per share.

Various inputs are used in determining the value of the fund's assets or liabilities. These inputs are categorized into three broad levels. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, an investment's level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement. The fund's assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the investment. Level 1 includes unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 includes other significant observable market-based inputs (including quoted prices for similar securities, interest rates, prepayment speed, and credit risk). Level 3 includes significant unobservable inputs, which may include the adviser's own assumptions in determining the fair value of investments. Other financial instruments are derivative instruments, such as futures contracts. The following is a summary of the levels used as of April 30, 2023 in valuing the fund's assets and liabilities:

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Notes to Financial Statements (unaudited) - continued

Financial Instruments	Level 1	Level 2	Level 3	Total
U.S. Treasury Bonds & U.S. Government Agencies & Equivalents	$—	$1,479,260,535	$—	$1,479,260,535
Municipal Bonds	—	20,044,073	—	20,044,073
U.S. Corporate Bonds	—	9,262,910	—	9,262,910
Residential Mortgage-Backed Securities	—	9,955,172	—	9,955,172
Commercial Mortgage-Backed Securities	—	19,536,964	—	19,536,964
Asset-Backed Securities (including CDOs)	—	2,836,881	—	2,836,881
Mutual Funds	2,422,187	—	—	2,422,187
Total	$2,422,187	$1,540,896,535	$—	$1,543,318,722
Other Financial Instruments
Futures Contracts – Assets	$411,954	$—	$—	$411,954
Futures Contracts – Liabilities	(346,363)	—	—	(346,363)

For further information regarding security characteristics, see the Portfolio of Investments.

Inflation-Adjusted Debt Securities — The fund invests in inflation-adjusted debt securities issued by the U.S. Treasury. The principal value of these debt securities is adjusted through income according to changes in the Consumer Price Index. These debt securities typically pay a fixed rate of interest, but this fixed rate is applied to the inflation-adjusted principal amount. The principal paid at maturity of the debt security is typically equal to the inflation-adjusted principal amount, or the security’s original par value, whichever is greater. Other types of inflation-adjusted securities may use other methods to adjust for other measures of inflation.

Foreign Currency Translation — Purchases and sales of foreign investments, income, and expenses are converted into U.S. dollars based upon currency exchange rates prevailing on the respective dates of such transactions or on the reporting date for foreign denominated receivables and payables. Gains and losses attributable to foreign currency exchange rates on sales of securities are recorded for financial statement purposes as net realized gains and losses on investments. Gains and losses attributable to foreign exchange rate movements on receivables, payables, income and expenses are recorded for financial statement purposes as foreign currency transaction gains and losses. That portion of both realized and unrealized gains and losses on investments that results from fluctuations in foreign currency exchange rates is not separately disclosed.

Derivatives — The fund uses derivatives primarily to increase or decrease exposure to a particular market or segment of the market, or security, to increase or decrease interest rate or currency exposure, or as alternatives to direct investments. Derivatives are used for hedging or non-hedging purposes. While hedging can reduce or eliminate losses, it can also reduce or eliminate gains. When the fund uses derivatives as an investment to increase market exposure, or for hedging purposes, gains and losses from derivative instruments may be substantially greater than the derivative’s original cost.

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Notes to Financial Statements (unaudited) - continued

The derivative instruments used by the fund during the period were futures contracts. Depending on the type of derivative, a fund may exit a derivative position by entering into an offsetting transaction with a counterparty or exchange, negotiating an agreement with the derivative counterparty, or novating the position to a third party. At April 30, 2023, the fund did not have any outstanding derivative instruments.

The following table presents, by major type of derivative contract, the fair value, on a gross basis, of the asset and liability components of derivatives held by the fund at April 30, 2023 as reported in the Statement of Assets and Liabilities:

		Fair Value (a)
Risk	Derivative Contracts	Asset Derivatives	Liability Derivatives
Interest Rate	Futures Contracts	$411,954	$(346,363)

(a)	Values presented in this table for futures contracts correspond to the values reported in the Portfolio of Investments. Only the current day net variation margin for futures contracts is reported separately within the Statement of Assets and Liabilities.

The following table presents, by major type of derivative contract, the realized gain (loss) on derivatives held by the fund for the six months ended April 30, 2023 as reported in the Statement of Operations:

Risk	Futures Contracts
Interest Rate	$(1,233,288)

The following table presents, by major type of derivative contract, the change in unrealized appreciation or depreciation on derivatives held by the fund for the six months ended April 30, 2023 as reported in the Statement of Operations:

Risk	Futures Contracts
Interest Rate	$65,591

Derivative counterparty credit risk is managed through formal evaluation of the creditworthiness of all potential counterparties. On certain, but not all, uncleared derivatives, the fund attempts to reduce its exposure to counterparty credit risk whenever possible by entering into an ISDA Master Agreement on a bilateral basis. The ISDA Master Agreement gives each party to the agreement the right to terminate all transactions traded under such agreement if there is a specified deterioration in the credit quality of the other party. Upon an event of default or a termination of the ISDA Master Agreement, the non-defaulting party has the right to close out all transactions traded under such agreement and to net amounts owed under each agreement to one net amount payable by one party to the other. This right to close out and net payments across all transactions traded under the ISDA Master Agreement could result in a reduction of the fund's credit risk to such counterparty equal to any amounts payable by the fund under the applicable transactions, if any.

Collateral and margin requirements differ by type of derivative. For cleared derivatives (e.g., futures contracts, cleared swaps, and exchange-traded options), margin requirements are set by the clearing broker and the clearing house and collateral, in the form of cash or securities, is posted by the fund directly with the clearing broker. Collateral terms are counterparty agreement specific for uncleared derivatives (e.g., forward foreign currency exchange contracts, uncleared swap agreements, and

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Notes to Financial Statements (unaudited) - continued

uncleared options) and collateral, in the form of cash and securities, is held in segregated accounts with the fund's custodian in connection with these agreements. For derivatives traded under an ISDA Master Agreement, which contains a credit support annex, the collateral requirements are netted across all transactions traded under such counterparty-specific agreement and an amount is posted from one party to the other to collateralize such obligations. Cash that has been segregated or delivered to cover the fund's collateral or margin obligations under derivative contracts, if any, will be reported separately in the Statement of Assets and Liabilities as restricted cash for uncleared derivatives and/or deposits with brokers for cleared derivatives. Securities pledged as collateral or margin for the same purpose, if any, are noted in the Portfolio of Investments. The fund may be required to make payments of interest on uncovered collateral or margin obligations with the broker. Any such payments are included in “Miscellaneous” expense in the Statement of Operations.

Futures Contracts — The fund entered into futures contracts which may be used to hedge against or obtain broad market exposure, interest rate exposure, currency exposure, or to manage duration. A futures contract represents a commitment for the future purchase or sale of an asset at a specified price on a specified date.

Upon entering into a futures contract, the fund is required to deposit with the broker, either in cash or securities, an initial margin in an amount equal to a specified percentage of the notional amount of the contract. Subsequent payments (variation margin) are made or received by the fund each day, depending on the daily fluctuations in the value of the contract, and are recorded for financial statement purposes as unrealized gain or loss by the fund until the contract is closed or expires at which point the gain or loss on futures contracts is realized.

The fund bears the risk of interest rates, exchange rates or securities prices moving unexpectedly, in which case, the fund may not achieve the anticipated benefits of the futures contracts and may realize a loss. While futures contracts may present less counterparty risk to the fund since the contracts are exchange traded and the exchange’s clearinghouse guarantees payments to the broker, there is still counterparty credit risk due to the insolvency of the broker. The fund’s maximum risk of loss due to counterparty credit risk is equal to the margin posted by the fund to the broker plus any gains or minus any losses on the outstanding futures contracts.

Indemnifications — Under the fund's organizational documents, its officers and Trustees may be indemnified against certain liabilities and expenses arising out of the performance of their duties to the fund. Additionally, in the normal course of business, the fund enters into agreements with service providers that may contain indemnification clauses. The fund's maximum exposure under these agreements is unknown as this would involve future claims that may be made against the fund that have not yet occurred.

Investment Transactions and Income — Investment transactions are recorded on the trade date. Interest income is recorded on the accrual basis. All premium and discount is amortized or accreted for financial statement purposes in accordance with U.S. generally accepted accounting principles. Interest payments received in additional securities are recorded on the ex-interest date in an amount equal to the value of the security on such date. In determining the net gain or loss on securities sold, the cost of securities is determined on the identified cost basis. Inflation-indexed bonds are fixed-income securities whose principal value is periodically adjusted upward or downward based on the rate of inflation. Interest is accrued based on the principal

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Notes to Financial Statements (unaudited) - continued

amount, which is adjusted for inflation. Any increase or decrease in the principal amount of an inflation-indexed bond is generally recorded as an increase or decrease in interest income, respectively, even though the adjusted principal is not received until maturity.

The fund may receive proceeds from litigation settlements. Any proceeds received from litigation involving portfolio holdings are reflected in the Statement of Operations in realized gain/loss if the security has been disposed of by the fund or in unrealized gain/loss if the security is still held by the fund. Any other proceeds from litigation not related to portfolio holdings are reflected as other income in the Statement of Operations.

To mitigate the counterparty credit risk on TBA transactions, mortgage dollar rolls, and other types of forward settling mortgage-backed and asset-backed security transactions, the fund whenever possible enters into a Master Securities Forward Transaction Agreement (“MSFTA”) on a bilateral basis with each of the counterparties with whom it undertakes a significant volume of transactions. The MSFTA gives each party to the agreement the right to terminate all transactions traded under such agreement if there is a specified deterioration in the credit quality of the other party. Upon an event of default or a termination of the MSFTA, the non-defaulting party has the right to close out all transactions traded under such agreement and to net amounts owed under each transaction to one net amount payable by one party to the other. This right to close out and net payments across all transactions traded under the MSFTA could result in a reduction of the fund's credit risk to such counterparty equal to any amounts payable by the fund under the applicable transactions, if any.

For mortgage-backed and asset-backed securities traded under a MSFTA, the collateral and margining requirements are contract specific. Collateral amounts across all transactions traded under such agreement are netted and an amount is posted from one party to the other to collateralize such obligations. Cash that has been pledged to cover the fund's collateral or margin obligations under a MSFTA, if any, will be reported separately on the Statement of Assets and Liabilities as restricted cash. Securities pledged as collateral or margin for the same purpose, if any, are noted in the Portfolio of Investments.

Tax Matters and Distributions — The fund intends to qualify as a regulated investment company, as defined under Subchapter M of the Internal Revenue Code, and to distribute all of its taxable income, including realized capital gains. As a result, no provision for federal income tax is required. The fund’s federal tax returns, when filed, will remain subject to examination by the Internal Revenue Service for a three year period. Management has analyzed the fund’s tax positions taken on federal and state tax returns for all open tax years and does not believe that there are any uncertain tax positions that require recognition of a tax liability. Foreign taxes, if any, have been accrued by the fund in the accompanying financial statements in accordance with the applicable foreign tax law. Foreign income taxes may be withheld by certain countries in which the fund invests. Additionally, capital gains realized by the fund on securities issued in or by certain foreign countries may be subject to capital gains tax imposed by those countries.

Distributions to shareholders are recorded on the ex-dividend date. Income and capital gain distributions are determined in accordance with income tax regulations, which may differ from U.S. generally accepted accounting principles. Certain capital accounts in the financial statements are periodically adjusted for permanent differences in order

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Notes to Financial Statements (unaudited) - continued

to reflect their tax character. These adjustments have no impact on net assets or net asset value per share. Temporary differences which arise from recognizing certain items of income, expense, gain or loss in different periods for financial statement and tax purposes will reverse at some time in the future.

Book/tax differences primarily relate to amortization and accretion of debt securities and wash sale loss deferrals.

The tax character of distributions made during the current period will be determined at fiscal year end. The tax character of distributions declared to shareholders for the last fiscal year is as follows:

	Year ended 10/31/22
Ordinary income (including any short-term capital gains)	$130,432,770

The federal tax cost and the tax basis components of distributable earnings were as follows:

As of 4/30/23
Cost of investments	$1,670,083,676
Gross appreciation	1,221,431
Gross depreciation	(127,986,385)
Net unrealized appreciation (depreciation)	$(126,764,954)
As of 10/31/22
Undistributed ordinary income	19,966,771
Capital loss carryforwards	(39,036,768)
Net unrealized appreciation (depreciation)	(195,156,831)

The aggregate cost above includes prior fiscal year end tax adjustments, if applicable.

As of October 31, 2022, the fund had capital loss carryforwards available to offset future realized gains. These net capital losses may be carried forward indefinitely and their character is retained as short-term and/or long-term losses. Such losses are characterized as follows:

Short-Term	$(30,856,824)
Long-Term	(8,179,944)
Total	$(39,036,768)

Multiple Classes of Shares of Beneficial Interest — The fund offers multiple classes of shares, which differ in their respective distribution and service fees. The fund's income, realized and unrealized gain (loss), and common expenses are allocated to shareholders based on the daily net assets of each class. Dividends are declared separately for each class. Differences in per share dividend rates are generally due to differences in separate class expenses. Class B and Class C shares will convert to

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Notes to Financial Statements (unaudited) - continued

Class A shares approximately eight years after purchase. The fund’s distributions declared to shareholders as reported in the Statements of Changes in Net Assets are presented by class as follows:

	Six months ended 4/30/23	Year ended 10/31/22
Class A	$2,685,262	$10,041,641
Class B	11,318	56,309
Class C	105,501	475,960
Class I	550,173	1,785,576
Class R1	18,175	60,150
Class R2	13,264	45,502
Class R3	35,440	142,441
Class R4	2,107	6,882
Class R6	34,080,527	117,818,309
Total	$37,501,767	$130,432,770

(3) Transactions with Affiliates

Investment Adviser — The fund has an investment advisory agreement with MFS to provide overall investment management and related administrative services and facilities to the fund. The management fee is computed daily and paid monthly at the following annual rates based on the fund's average daily net assets:

Up to $1 billion	0.50%
In excess of $1 billion and up to $2.5 billion	0.35%
In excess of $2.5 billion and up to $5 billion	0.30%
In excess of $5 billion	0.29%

The investment adviser has agreed in writing to reduce its management fee to 0.40% of the fund’s average daily net assets annually up to $1 billion. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until February 29, 2024. For the six months ended April 30, 2023, this management fee reduction amounted to $495,892, which is included in the reduction of total expenses in the Statement of Operations. MFS has also agreed in writing to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. MFS has agreed in writing to waive at least 0.01% of its management fee as part of this agreement. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue at least until February 29, 2024. For the six months ended April 30, 2023, this management fee reduction amounted to $98,921, which is included in the reduction of total expenses in the Statement of Operations. The management fee incurred for the six months ended April 30, 2023 was equivalent to an annual effective rate of 0.37% of the fund's average daily net assets.

The investment adviser has agreed in writing to pay a portion of the fund’s total annual operating expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, certain tax reclaim recovery expenses (including contingency fees and

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Notes to Financial Statements (unaudited) - continued

closing agreement expenses), and investment-related expenses, such that total fund operating expenses do not exceed the following rates annually of each class’s average daily net assets:

Classes
A	B	C	I	R1	R2	R3	R4	R6
0.67%	1.42%	1.52%	0.52%	1.52%	1.02%	0.77%	0.52%	0.44%

This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until February 29, 2024. For the six months ended April 30, 2023, the fund’s actual operating expenses did not exceed the limit and therefore, the investment adviser did not pay any portion of the fund’s expenses related to this agreement.

Distributor — MFS Fund Distributors, Inc. (MFD), a wholly-owned subsidiary of MFS, as distributor, received $1,201 for the six months ended April 30, 2023, as its portion of the initial sales charge on sales of Class A shares of the fund.

The Board of Trustees has adopted a distribution plan for certain share classes pursuant to Rule 12b-1 of the Investment Company Act of 1940.

The fund's distribution plan provides that the fund will pay MFD for services provided by MFD and financial intermediaries in connection with the distribution and servicing of certain share classes. One component of the plan is a distribution fee paid to MFD and another component of the plan is a service fee paid to MFD. MFD may subsequently pay all, or a portion, of the distribution and/or service fees to financial intermediaries.

Distribution Plan Fee Table:

	Distribution Fee Rate (d)	Service Fee Rate (d)	Total Distribution Plan (d)	Annual Effective Rate (e)	Distribution and Service Fee
Class A	—	0.25%	0.25%	0.15%	$ 136,926
Class B	0.75%	0.25%	1.00%	0.90%	2,541
Class C	0.75%	0.25%	1.00%	1.00%	24,510
Class R1	0.75%	0.25%	1.00%	1.00%	4,457
Class R2	0.25%	0.25%	0.50%	0.50%	1,422
Class R3	—	0.25%	0.25%	0.25%	1,685
Total Distribution and Service Fees					$171,541

(d)

In accordance with the distribution plan for certain classes, the fund pays distribution and/or service fees equal to these annual percentage rates of each class’s average daily net assets. The distribution and service fee rates disclosed by class represent the current rates in effect at the end of the reporting period. Any rate changes, if applicable, are detailed below.

(e)

The annual effective rates represent actual fees incurred under the distribution plan for the six months ended April 30, 2023 based on each class's average daily net assets. 0.10% of the Class A and Class B service fee is currently being waived under a written waiver arrangement. For the six months ended April 30, 2023, this waiver amounted to $54,770 and $254, respectively, and is included in the reduction of total expenses in the Statement of Operations. These written waiver agreements will continue until modified by the fund’s Board of Trustees, but such agreements will continue at least until February 29, 2024. MFD has voluntarily agreed to rebate a portion of each class's 0.25% service fee attributable to

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Notes to Financial Statements (unaudited) - continued

accounts for which there is no financial intermediary specified on the account except for accounts attributable to MFS or its affiliates' seed money. For the six months ended April 30, 2023, this rebate amounted to $32 for Class A, and is included in the reduction of total expenses in the Statement of Operations.

Certain Class A shares are subject to a contingent deferred sales charge (CDSC) in the event of a shareholder redemption within 18 months of purchase. Class B shares are subject to a CDSC in the event of a shareholder redemption within six years of purchase. Class C shares are subject to a CDSC in the event of a shareholder redemption within 12 months of purchase. All contingent deferred sales charges are paid to MFD and during the six months ended April 30, 2023, were as follows:

	Amount
Class A	$2,139
Class B	2
Class C	25

Shareholder Servicing Agent — MFS Service Center, Inc. (MFSC), a wholly-owned subsidiary of MFS, receives a fee from the fund for its services as shareholder servicing agent calculated as a percentage of the average daily net assets of the fund as determined periodically under the supervision of the fund's Board of Trustees. For the six months ended April 30, 2023, the fee was $13,378, which equated to 0.0018% annually of the fund's average daily net assets. MFSC also receives reimbursement from the fund for out-of-pocket expenses, sub-accounting and other shareholder servicing costs which may be paid to affiliated and unaffiliated service providers. Class R6 shares do not incur sub-accounting fees. For the six months ended April 30, 2023, these out-of-pocket expenses, sub-accounting and other shareholder servicing costs amounted to $63,354.

Administrator — MFS provides certain financial, legal, shareholder communications, compliance, and other administrative services to the fund. Under an administrative services agreement, the fund reimburses MFS the costs incurred to provide these services. The fund is charged an annual fixed amount of $17,500 plus a fee based on average daily net assets. The administrative services fee incurred for the six months ended April 30, 2023 was equivalent to an annual effective rate of 0.0154% of the fund's average daily net assets.

Trustees’ and Officers’ Compensation — The fund pays compensation to independent Trustees in the form of a retainer, attendance fees, and additional compensation to Board and Committee chairpersons. The fund does not pay compensation directly to Trustees or officers of the fund who are also officers of the investment adviser, all of whom receive remuneration from MFS for their services to the fund. Certain officers and Trustees of the fund are officers or directors of MFS, MFD, and MFSC.

Other — The fund invests in the MFS Institutional Money Market Portfolio which is managed by MFS and seeks current income consistent with preservation of capital and liquidity. This money market fund does not pay a management fee to MFS but does incur investment and operating costs.

At April 30, 2023, MFS held approximately 65% of the outstanding shares of Class R4.

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Notes to Financial Statements (unaudited) - continued

(4) Portfolio Securities

For the six months ended April 30, 2023, purchases and sales of investments, other than short-term obligations, were as follows:

	Purchases	Sales
U.S. Government securities	$310,236,612	$307,758,582
Non-U.S. Government securities	—	4,982,792

(5) Shares of Beneficial Interest

The fund's Declaration of Trust permits the Trustees to issue an unlimited number of full and fractional shares of beneficial interest. Transactions in fund shares were as follows:

	Six months ended 4/30/23		Year ended 10/31/22
	Shares	Amount	Shares	Amount
Shares sold
Class A	692,432	$6,521,837	6,487,495	$70,354,613
Class B	80	750	21,839	228,450
Class C	44,715	420,333	532,794	5,805,006
Class I	1,127,339	10,589,568	3,138,000	34,468,021
Class R1	2,195	20,362	15,922	167,580
Class R2	4,178	39,140	11,986	127,063
Class R3	6,788	64,243	107,774	1,170,110
Class R4	222	2,083	399	4,175
Class R6	5,980,138	56,453,690	13,079,003	139,082,928
	7,858,087	$74,112,006	23,395,212	$251,407,946
Shares issued to shareholders in reinvestment of distributions
Class A	280,477	$2,632,612	951,666	$9,811,916
Class B	1,178	10,982	5,183	53,914
Class C	11,332	105,501	46,019	475,562
Class I	58,304	548,114	173,182	1,780,036
Class R1	1,959	18,175	5,899	60,150
Class R2	1,380	12,903	4,288	44,265
Class R3	3,781	35,440	13,673	142,441
Class R4	224	2,107	665	6,882
Class R6	3,615,189	34,052,989	11,294,250	117,706,015
	3,973,824	$37,418,823	12,494,825	$130,081,181

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Notes to Financial Statements (unaudited) - continued

	Six months ended 4/30/23		Year ended 10/31/22
	Shares	Amount	Shares	Amount
Shares reacquired
Class A	(2,608,292)	$(24,547,762)	(4,823,031)	$(49,513,504)
Class B	(17,531)	(163,229)	(61,370)	(639,683)
Class C	(174,384)	(1,625,353)	(533,074)	(5,578,493)
Class I	(674,269)	(6,349,916)	(2,072,673)	(21,704,293)
Class R1	(1,103)	(10,240)	(1,116)	(11,862)
Class R2	(11,556)	(109,068)	(13,180)	(142,692)
Class R3	(80,999)	(757,226)	(145,147)	(1,555,410)
Class R4	(10)	(98)	(23)	(242)
Class R6	(6,730,756)	(62,998,052)	(21,110,485)	(220,750,273)
	(10,298,900)	$(96,560,944)	(28,760,099)	$(299,896,452)
Net change
Class A	(1,635,383)	$(15,393,313)	2,616,130	$30,653,025
Class B	(16,273)	(151,497)	(34,348)	(357,319)
Class C	(118,337)	(1,099,519)	45,739	702,075
Class I	511,374	4,787,766	1,238,509	14,543,764
Class R1	3,051	28,297	20,705	215,868
Class R2	(5,998)	(57,025)	3,094	28,636
Class R3	(70,430)	(657,543)	(23,700)	(242,859)
Class R4	436	4,092	1,041	10,815
Class R6	2,864,571	27,508,627	3,262,768	36,038,670
	1,533,011	$14,969,885	7,129,938	$81,592,675

The fund is one of several mutual funds in which certain MFS funds may invest. The MFS funds do not invest in the underlying funds for the purpose of exercising management or control. At the end of the period, the MFS Moderate Allocation Fund, the MFS Conservative Allocation Fund, the MFS Growth Allocation Fund, the MFS Lifetime Income Fund, the MFS Lifetime 2030 Fund, the MFS Lifetime 2025 Fund, the MFS Lifetime 2035 Fund, and the MFS Lifetime 2040 Fund were the owners of record of approximately 29%, 25%, 19%, 4%, 4%, 2%, 2%, and 2%, respectively, of the value of outstanding voting shares of the fund. In addition, the MFS Lifetime 2045 Fund, the MFS Lifetime 2050 Fund, the MFS Lifetime 2055 Fund, the MFS Lifetime 2060 Fund, and the MFS Lifetime 2065 Fund were each the owners of record of less than 1% of the value of outstanding voting shares of the fund.

Effective June 1, 2019, purchases of the fund’s Class B shares were closed to new and existing investors subject to certain exceptions. On March 30, 2023, the fund announced that effective after the close of business on September 29, 2023, purchases of Class R1 and Class R2 shares will be closed to new eligible investors.

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(6) Line of Credit

The fund and certain other funds managed by MFS participate in a $1.45 billion unsecured committed line of credit of which $1.2 billion is reserved for use by the fund and certain other MFS U.S. funds. The line of credit is provided by a syndicate of banks under a credit agreement. Borrowings may be made for temporary financing needs. Interest is charged to each fund, based on its borrowings, generally at a rate equal to the highest of 1) Daily Simple SOFR (Secured Overnight Financing Rate) plus 0.10%, 2) the Federal Funds Effective Rate, or 3) the Overnight Bank Funding Rate, each plus an agreed upon spread. A commitment fee, based on the average daily unused portion of the committed line of credit, is allocated among the participating funds. The line of credit expires on March 14, 2024 unless extended or renewed. In addition, the fund and other funds managed by MFS have established unsecured uncommitted borrowing arrangements with certain banks for temporary financing needs. Interest is charged to each fund, based on its borrowings, at rates equal to customary reference rates plus an agreed upon spread. For the six months ended April 30, 2023, the fund’s commitment fee and interest expense were $4,028 and $0, respectively, and are included in “Miscellaneous” expense in the Statement of Operations.

(7) Investments in Affiliated Issuers

An affiliated issuer may be considered one in which the fund owns 5% or more of the outstanding voting securities, or a company which is under common control. For the purposes of this report, the following were affiliated issuers:

Affiliated Issuers	Beginning Value	Purchases	Sales Proceeds	Realized Gain (Loss)	Change in Unrealized Appreciation or Depreciation	Ending Value
MFS Institutional Money Market Portfolio	$1,750,415	$143,619,354	$142,934,894	$(13,038)	$350	$2,422,187

Affiliated Issuers	Dividend Income	Capital Gain Distributions
MFS Institutional Money Market Portfolio	$125,642	$—

(8) LIBOR Transition

Certain of the fund's investments, including investments in certain debt instruments and derivatives (if any), as well as borrowings by the fund and certain other contractual arrangements of the fund, may be based on the London Interbank Offered Rate (“LIBOR”). In 2017, the regulatory authority that oversees financial services firms in the United Kingdom announced plans to transition away from LIBOR by the end of 2021. In March 2021, the administrator of LIBOR announced the extension of the publication of the more commonly used U.S. dollar LIBOR settings to the end of June 2023. Although the full impacts of the transition away from LIBOR are not fully known, the transition may result in, among other things, an increase in volatility or illiquidity of the markets for instruments that currently rely on LIBOR to determine interest rates and this could have an adverse impact on the fund's performance. With respect to the fund's accounting for investments, including investments in certain debt instruments and derivatives, as well as borrowings by the fund and any other contractual arrangements of the fund that undergo reference rate-related modifications as a result of the

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Statement Regarding Liquidity Risk Management Program

The fund has adopted and implemented a liquidity risk management program (the “Program”) as required by Rule 22e-4 under the Investment Company Act of 1940, as amended. The fund’s Board of Trustees (the “Board”) has designated MFS as the administrator of the Program. The Program is reasonably designed to assess and manage the liquidity risk of the fund. Liquidity risk is the risk that the fund could not meet requests to redeem shares issued by the fund without significant dilution of remaining investors' interests.

MFS provided a written report to the Board for consideration at its March 2023 meeting that addressed the operation of the Program and provided an assessment of the adequacy and effectiveness of the Program during the period from January 1, 2022 to December 31, 2022 (the “Covered Period”). The report concluded that during the Covered Period the Program had operated effectively in all material respects and had adequately and effectively been implemented to assess and manage the fund’s liquidity risk. MFS also reported that there were no liquidity events that impacted the fund or its ability to timely meet redemptions without dilution to existing shareholders during the Covered Period.

There can be no assurance that the Program will achieve its objectives in the future. Further information on liquidity risk, and other principal risks to which an investment in the fund may be subject, can be found in the prospectus.

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Proxy Voting Policies and Information

MFS votes proxies on behalf of the fund pursuant to proxy voting policies and procedures that are available without charge, upon request, by calling 1-800-225-2606, by visiting mfs.com/proxyvoting, or by visiting the SEC’s Web site at http://www.sec.gov.

Information regarding how the fund voted proxies relating to portfolio securities during the most recent twelve-month period ended June 30 is available by August 31 of each year without charge by visiting mfs.com/proxyvoting, or by visiting the SEC’s Web site at http://www.sec.gov.

Quarterly Portfolio Disclosure

The fund files a complete schedule of portfolio holdings with the SEC for the first and third quarters of each fiscal year as an exhibit to its reports on Form N-PORT. The fund's Form N-PORT reports are available on the SEC's Web site at http://www.sec.gov. A shareholder can obtain the portfolio holdings report for the first and third quarters of the fund's fiscal year at mfs.com/openendfunds by choosing the fund's name and then scrolling to the “Resources” section and clicking on the “Prospectus and Reports” tab.

Further Information

From time to time, MFS may post important information about the fund or the MFS Funds on the MFS Web site (mfs.com). This information is available at https://www.mfs.com/announcements or at mfs.com/openendfunds by choosing the fund’s name and then scrolling to the “Resources” section and clicking on the “Announcements” tab, if any.

Information About Fund Contracts and Legal Claims

The fund has entered into contractual arrangements with an investment adviser, administrator, distributor, shareholder servicing agent, and custodian who each provide services to the fund. Unless expressly stated otherwise, shareholders are not parties to, or intended beneficiaries of these contractual arrangements, and these contractual arrangements are not intended to create any shareholder right to enforce them against the service providers or to seek any remedy under them against the service providers, either directly or on behalf of the fund.

Under the Trust’s By-Laws and Declaration of Trust, any claims asserted against or on behalf of the MFS Funds, including claims against Trustees and Officers, must be brought in state and federal courts located within the Commonwealth of Massachusetts.

Provision of Financial Reports and Summary Prospectuses

The fund produces financial reports every six months and updates its summary prospectus and prospectus annually. To avoid sending duplicate copies of materials to households, only one copy of the fund’s annual and semiannual report and summary prospectus may be mailed to shareholders having the same last name and residential address on the fund’s records. However, any shareholder may contact MFSC (please see back cover for address and telephone number) to request that copies of these reports and summary prospectuses be sent personally to that shareholder.

Item 1(b):

Not applicable.

ITEM 2. CODE OF ETHICS.

During the period covered by this report, the Registrant has not amended any provision in its Code of Ethics (the "Code") that relates to an element of the Code's definition enumerated in paragraph (b) of Item 2 of this Form N-CSR. During the period covered by this report, the Registrant did not grant a waiver, including an implicit waiver, from any provision of the Code.

ITEM 3. AUDIT COMMITTEE FINANCIAL EXPERT.

Not applicable for semi-annual reports.

ITEM 4. PRINCIPAL ACCOUNTANT FEES AND SERVICES.

Not applicable for semi-annual reports.

ITEM 5. AUDIT COMMITTEE OF LISTED REGISTRANTS.

Not applicable to the Registrant.

ITEM 6. INVESTMENTS

A schedule of investments for each series covered by this Form N-CSR is included as part of the report to shareholders of such series under Item 1(a) of this Form N-CSR.

ITEM 7. DISCLOSURE OF PROXY VOTING POLICIES AND PROCEDURES FOR CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable to the Registrant.

ITEM 8. PORTFOLIO MANAGERS OF CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable to the Registrant.

ITEM 9. PURCHASES OF EQUITY SECURITIES BY CLOSED-END MANAGEMENT INVESTMENT COMPANY AND AFFILIATED PURCHASERS.

Not applicable to the Registrant.

ITEM 10. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.

There were no material changes to the procedures by which shareholders may send recommendations to the Board for nominees to the Registrant's Board since the Registrant last provided disclosure as to such procedures in response to the requirements of Item 407 (c)(2)(iv) of Regulation S-K or this Item.

ITEM 11. CONTROLS AND PROCEDURES.

(a)Based upon their evaluation of the effectiveness of the registrant's disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940 (the "Act")) as conducted within 90 days of the filing date of this report on Form N-CSR, the Registrant's principal financial officer and principal executive officer have concluded that those disclosure controls and procedures provide reasonable assurance that the material information required to be disclosed by the Registrant on this report is recorded, processed, summarized and reported within the time periods specified in the Securities and Exchange Commission's rules and forms.

(b)There were no changes in the Registrant's internal controls over financial reporting (as defined in Rule 30a-3(d) under the Act) that occurred during the period covered by the report that have materially affected, or are reasonably likely to materially affect, the Registrant's internal control over financial reporting.

ITEM 12. DISCLOSURE OF SECURITIES LENDING ACTIVITIES FOR CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable to the Registrant.

ITEM 13. EXHIBITS.

(a)(1) Any code of ethics, or amendment thereto, that is the subject of the disclosure required by Item 2, to the extent that the registrant intends to satisfy the Item 2 requirements through filing of an exhibit: Not applicable.

(2)A separate certification for each principal executive officer and principal financial officer of the registrant as required by Rule 30a-2(a) under the Act (17 CFR 270.30a-2): Attached hereto as EX-99.302CERT.

(3)Any written solicitation to purchase securities under Rule 23c-1 under the Act (17 CFR 270.23c-1) sent or given during the period covered by the report by or on behalf of the registrant to 10 or more persons. Not applicable.

(4)Change in the registrant's independent public accountant. Not applicable.

(b)If the report is filed under Section 13(a) or 15(d) of the Exchange Act, provide the certifications required by Rule 30a-2(b) under the Act (17 CFR 270.30a-2(b)), Rule 13a-14(b) or Rule 15d-14(b) under the Exchange Act (17 CFR 240.13a-14(b) or 240.15d-14(b)) and Section 1350 of Chapter 63 of Title 18 of the United States Code (18 U.S.C. 1350) as an exhibit. A certification furnished pursuant to this paragraph will not be deemed "filed" for the purposes of Section 18 of the Exchange Act (15 U.S.C. 78r), or otherwise subject to the liability of that section. Such certification will not be deemed to be incorporated by reference into any filing under the Securities Act of 1933 or the Exchange Act, except to the extent that the registrant specifically incorporates it by reference. Attached hereto as EX-99.906CERT.

Notice

A copy of the Amended and Restated Declaration of Trust, as amended, of the Registrant is on file with the Secretary of State of The Commonwealth of Massachusetts and notice is hereby given that this instrument is executed on behalf of the Registrant by an officer of the Registrant as an officer and not individually and the obligations of or arising out of this instrument are not binding upon any of the Trustees or shareholders individually, but are binding only upon the assets and property of the respective constituent series of the Registrant.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant) MFS SERIES TRUST IX

By (Signature and Title)*

/S/ DAVID L. DILORENZO

David L. DiLorenzo, President

Date: June 15, 2023

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By (Signature and Title)*

/S/ DAVID L. DILORENZO

David L. DiLorenzo, President (Principal Executive Officer)

Date: June 15, 2023

By (Signature and Title)*

/S/ JAMES O. YOST

James O. Yost, Treasurer (Principal Financial Officer and Accounting Officer) Date: June 15, 2023

* Print name and title of each signing officer under his or her signature.

Portfolio composition	1
Expense table	3
Portfolio of investments	5
Statement of assets and liabilities	9
Statement of operations	11
Statements of changes in net assets	12
Financial highlights	13
Notes to financial statements	19
Statement regarding liquidity risk management program	33
Proxy voting policies and information	34
Quarterly portfolio disclosure	34
Further information	34
Information about fund contracts and legal claims	34
Provision of financial reports and summary prospectuses	34

	Net assets	Shares outstanding	Net asset value per share (a)
Class A	$104,106,111	10,936,151	$9.52
Class B	423,535	44,837	9.45
Class C	4,386,683	465,126	9.43
Class I	28,071,166	2,944,064	9.53
Class R1	917,347	97,552	9.40
Class R2	542,051	57,114	9.49
Class R3	872,030	91,640	9.52
Class R4	89,991	9,450	9.52
Class R6	1,406,745,208	147,115,249	9.56

	Six months ended	Year ended
	4/30/23 (unaudited)	10/31/22
Change in net assets
From operations
Net investment income (loss)	$24,735,720	$102,859,374
Net realized gain (loss)	(32,214,123)	(18,118,725)
Net unrealized gain (loss)	71,147,228	(292,023,302)
Change in net assets from operations	$63,668,825	$(207,282,653)
Total distributions to shareholders	$(37,501,767)	$(130,432,770)
Change in net assets from fund share transactions	$14,969,885	$81,592,675
Total change in net assets	$41,136,943	$(256,122,748)
Net assets
At beginning of period	1,505,017,179	1,761,139,927
At end of period	$1,546,154,122	$1,505,017,179