`/fast` toggle off leaves model on Opus 4.6 instead of restoring default (4.7)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

Toggling /fast on then off leaves the session on Opus 4.6 instead of restoring the
default model (Opus 4.7). Opus 4.6 is not available as a selection in /model, so the
user ends up on a model they cannot normally choose.

What Should Happen?

Either:

• /fast off restores the model that was active before /fast was toggled on, or
• Opus 4.6 is available as a /model selection, so the post-fast state is reachable

through normal UI

Currently /fast off puts the user on a model (Opus 4.6 non-fast) that cannot be
selected via /model.

Steps to Reproduce

1. Launch Claude Code on Claude Max 20x (default model: Opus 4.7)
2. Run /model — confirms Opus 4.7 (1M context) (default). Note: Opus 4.6 is not listed as a choice
3. Run /fast — fast mode ON, model switches to Opus 4.6
4. Run /fast — fast mode OFF
5. Check status bar → shows Model: Opus 4.6 (1M context)

Expected at step 5: Model restored to Opus 4.7 (the default)
Actual at step 5: Model stuck on Opus 4.6 — a model not available via /model

Additionally, the model's system prompt metadata still claims Opus 4.7 after step 5, so
the model self-reports as 4.7 when asked, contradicting the status bar.

Claude Model

Opus

Is this a regression?

I don't know

Claude Code Version

2.1.126

Platform

Claude Max 20x

Operating System

Linux (Kubuntu, 6.19.4)

Terminal/Shell

bash

Additional Information

Since Opus 4.6 is not a /model selection, /fast on→off is currently the only way to
land on it — making this both a bug (wrong model restored) and an unintended state (model
not normally reachable through the UI).

Related: #44819 (VS Code model picker not updating on fast mode switch — different surface,
possibly shared state-management root cause).