Cover - shares	9 Months Ended
	Sep. 30, 2023	Nov. 06, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-41696
Entity Registrant Name	ACELYRIN, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-2406735
Entity Address, Address Line One	4149 Liberty Canyon Road
Entity Address, City or Town	Agoura Hills
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91301
City Area Code	805
Local Phone Number	730-0360
Title of 12(b) Security	Common Stock ($0.00001 par value)
Trading Symbol	SLRN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		97,339,494
Entity Central Index Key	0001962918
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Amendment Flag	false