Fast mode billing bug

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Fast mode is enabled/usable while "usage credits" are turned OFF (and no charges appear)
Summary
Fast mode (/fast) shows as enabled and is usable, even though my account has usage credits turned off. Per the fast mode docs, fast mode requires usage credits to be turned on ("your account must have usage credits turned on, which allows billing beyond your plan's included usage"). With credits off, fast mode should not be available/active — but it is, and no fast-mode charges are appearing.

Steps to reproduce
Confirm usage credits are OFF for the account.
In Claude Code, run /fast (or observe the fast-mode indicator) — it shows enabled.
Use Claude Code normally with fast mode shown as on.
Check billing/usage — no fast-mode charges appear.
Expected behavior
With usage credits off, fast mode should be unavailable (cannot be enabled / does not engage), per the documented precondition that fast mode requires usage credits on.

Actual behavior
Fast mode shows as enabled and usable with usage credits off, and nothing is billed. This is the documented-as-impossible state — so either:

the fast-mode indicator is on but fast inference isn't actually engaging (cosmetic/indicator bug), or
the credits-on gating is being bypassed and fast inference runs without a billing path.
I can't determine which from the client side. Flagging so the metering/gating can be checked on the backend.

Additional context
No fastMode key is present in ~/.claude/settings.json or the project .claude/settings.local.json, so the "on" state is not coming from a persisted local settings flag.
Environment
Claude Code version: 2.1.175
Model: Opus 4.8 (1M context) (claude-opus-4-8)
OS: macOS 27.0 (build 26A5353q)
Plan: usage credits OFF
Question
Is fast-mode-on-with-credits-off expected for any plan/configuration, or is this a gating bug? If it's a gating bypass, will charges post retroactively?

What Should Happen?

should not allow fast mode

Error Messages/Logs

Steps to Reproduce

turn on fast mode

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude 1.12603.1 (3df4fd) 2026-06-11T16:57:36.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_