The reason we (GitHub) kept the new tokens to 40 characters, matching the length of our old tokens, was to make this change as backwards compatible as possible.

The reason we (GitHub) kept the new tokens to 40 characters, matching the length of our old tokens, was to make this change as backwards compatible as possible. We’ve never documented or committed to our tokens being 40 characters long, but they’ve been that way a long time and there may be software out there storing them in a fixed length database columns. If you use a service you’re worried the change may break I’d recommend minting a new token and trying it, perhaps on a new account on that service, before revoking your old one. (We do plan to increase the length of our tokens in future, but not before July 2021 at the earliest.)