We describe the Spider ight cryostat, which is designed to cool six millimeter-wavelength telescopes during an Antarctic

long-duration balloon ight. The cryostat, one of the largest to have own on a stratospheric payload, uses liquid 4He

to deliver cooling power to stages at 4.2 and 1.6 K. Stainless steel capillaries facilitate a high ow impedance connection

between the main liquid helium tank and a smaller superuid tank, allowing the latter to operate at 1.6 K as long as

there is liquid in the 4.2 K main tank. Each telescope houses a closed cycle 3He adsorption refrigerator that further cools

the focal planes down to 300 mK. Liquid helium vapor from the main tank is routed through heat exchangers that cool

radiation shields, providing negative thermal feedback. The system performed successfully during a 17 day ight in the

2014{2015 Antarctic summer. The cryostat had a total hold time of 16.8 days, with 15.9 days occurring during ight.