Model configuration changedmodel-config
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Upstream edited this page at 4 Oct 2026 06:13 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 4 Oct 2026 06:37 UTC.
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265265* **[Automatic model fallback](#automatic-model-fallback)**: a fallback whose target is excluded does not run, so the flagged request ends with a refusal instead
266266* **[Auto mode classifier](/docs/en/permission-modes#eliminate-prompts-with-auto-mode)**: the classifier's Claude Sonnet 5 default applies only when the allowlist permits Sonnet 5. When it's excluded, the classifier runs on the session's model, which the allowlist already governs, or on an Opus model when the session runs on a [Fable model](#work-with-fable). On providers other than the Anthropic API, that Opus fallback runs on the model you set in `ANTHROPIC_DEFAULT_OPUS_MODEL` or otherwise on Opus 5, without consulting the allowlist. Requires Claude Code v2.1.210 or later
267267* **[Fast mode](/docs/en/fast-mode)**: enabling fast mode is refused when the model the session would run on afterward is outside the allowlist
268* **Availability fallback on Amazon Bedrock and Google Cloud's Agent Platform**: when your account loses access to a model mid-session, the switch to another model skips excluded models. The startup model checks on [Amazon Bedrock](/docs/en/amazon-bedrock#when-your-organization-enforces-a-model-allowlist) and [Google Cloud's Agent Platform](/docs/en/google-vertex-ai#when-your-organization-enforces-a-model-allowlist) skip excluded models only when managed settings also set [`enforceAvailableModels`](#enforce-the-allowlist-for-the-default-model)
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269270```json theme={null}
270271{
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