Unclear Which models fail the check that triggers this notice is not stated.
What
When you start a fresh session, not one you resume, and the model fails a check, Claude Code shows a notice. It says Claude Code isn't tested on this model and suggests running /model to switch.
Why
If you are on a model Claude Code hasn't been tested with, you are told at the start, along with the command to change it.
Names in the bundle/model
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up /model, on overview.
* We’ve deprecated [fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) for Claude Opus 4.8, with removal on November 30, 2026. After removal, requests to `claude-opus-4-8` with `speed: "fast"` will return an error.…release-notes/overview see the edit
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
Which models fail the check that triggers this notice is not stated.
Anthropic's documentation agrees
Anthropic's documentation has since written up /model, on overview.