Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2024	Nov. 07, 2024
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
Document Transition Report	false
Entity File Number	001-42143
Entity Registrant Name	Alumis Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	86-1771129
Entity Address, Address Line One	280 East Grand Avenue
Entity Address, City or Town	South San Francisco
Entity Address State Or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	231-6625
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	ALMS
Security Exchange Name	NASDAQ
Entity Central Index Key	0001847367
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Amendment Flag	false
Voting common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		47,222,419
Non-voting common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		7,184,908