[teraflop]

I don't see anything on the landing page either, but this text from the "overview" page of the documentation seems to imply debit:

> When an issued card is used to make a purchase, an authorization request is created. If approved, the authorized amount is held in reserve from your account balance. [...] The merchant then captures (clears) the authorization, at which point a transaction is created and the held funds are deducted from your account.

[brentjanderson]

This implies debit as the underlying mechanism for completing the transaction, however one could presumably build a credit-based business using these cards. If XYZ company issues a Stripe card under a credit model, then XYZ company would be footing the bill using their Stripe balance, and the cardholder would then have a credit balance with XYZ company.