You'll noticeTier: how much it should matter to you
2Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
Auto ModeArea: what it touches
ImprovementsKind: in v2.1.288,
ImprovementsSection of the release
What
ANTHROPIC_DEFAULT_SONNET_MODEL is an environment variable, a setting passed to Claude Code by the shell it starts from. It sets which model the sonnet alias stands for. Auto mode also uses it to choose the model for its classifier.
If the variable names a model that is on an exclusion list, Claude Code now drops it for the classifier and uses the Sonnet 5 default instead. It logs the reason once. Before, any model that passed the usual validity check was used.
Why
This matters if you use auto mode and pin the Sonnet model, for example on a third-party provider. The classifier may now run on a different model from the one you set.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtWhich models are on the exclusion list is not stated.
Anthropic's release notes agreeChanged the client-side auto mode classifier to ignore an ANTHROPIC_DEFAULT_SONNET_MODEL pin that names Claude Sonnet 5.5 or Opus 5.5 and…
