Unclear Whether claude-mythos-5 now actually receives the lean prompt depends on the rest of the check, which is not known.
What
Claude Code can send the model a leaner variant of its instructions, and it decides which models get it. Two things changed in that decision:
claude-mythos-5, and models matched by a related family check, are no longer ruled out at the very start. They now go through the same name-based checks as other models, which look for names such as claude-3-, haiku and sonnet.- The model name is now worked out in a fixed, repeatable way before those checks run.
A remote setting called lean_prompt still takes priority over all of this when it is sent.
Why
This can change which version of the instructions claude-mythos-5 and similar models receive.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
Whether `claude-mythos-5` now actually receives the lean prompt depends on the rest of the check, which is not known.