v3.26.1
Document and Entity Information
Jul. 14, 2026
Document And Entity Information [Line Items]  
Entity Registrant Name Churchill Capital Corp IX/Cayman
Amendment Flag false
Entity Central Index Key 0002006291
Document Type 8-K
Document Period End Date Jul. 14, 2026
Entity Incorporation State Country Code E9
Entity File Number 001-42041
Entity Tax Identification Number 86-1885237
Entity Address, Address Line One 640 Fifth Avenue
Entity Address, Address Line Two 14th Floor
Entity Address, City or Town New York
Entity Address, State or Province NY
Entity Address, Postal Zip Code 10019
City Area Code (212)
Local Phone Number 380-7500
Written Communications false
Soliciting Material false
Pre Commencement Tender Offer false
Pre Commencement Issuer Tender Offer false
Entity Emerging Growth Company true
Entity Ex Transition Period false
Units Each Consisting Of One Class A Ordinary Share And One Quarter Of One Redeemable Warrant [Member]  
Document And Entity Information [Line Items]  
Security 12b Title Units, each consisting of one Class A ordinary share and one-quarter of one redeemable warrant
Trading Symbol CCIXU
Security Exchange Name NASDAQ
Capital Unit, Class A [Member]  
Document And Entity Information [Line Items]  
Security 12b Title Class A ordinary shares, par value $0.0001 per share
Trading Symbol CCIX
Security Exchange Name NASDAQ
Warrants Each Whole Warrant Exercisable For One Class A Ordinary Share At An Exercise Price Of 11.50 Per Share [Member]  
Document And Entity Information [Line Items]  
Security 12b Title Warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50 per share
Trading Symbol CCIXW
Security Exchange Name NASDAQ