It's explicitly called out as excluded in the blue info bubble they have there.

> Fast mode usage is billed directly to extra usage, even if you have remaining usage on your plan. This means fast mode tokens do not count against your plan’s included usage and are charged at the fast mode rate from the first token.

https://code.claude.com/docs/en/fast-mode#requirements

I think this is just worded in a misleading way. It’s available to all users, but it’s not included as part of the plan.