From website footer:

> Brex is a financial technology company, not a bank. The Brex business account consists of Checking, a commercial checking account provided by Column N.A., Member FDIC, and Treasury and Vault, cash management services provided by Brex Treasury LLC, Member FINRA/SIPC.

Stripe is a much bigger business with hands in all sorts of instruments, chiefly payments processing.

Do you know how many businesses move money on Stripe rails? It's wild.