Model configuration changedmodel-config
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Upstream edited this page at 2 Oct 2026 02:36 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 2 Oct 2026 02:37 UTC.
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260260* **[Fallback model chains](#fallback-model-chains)**: entries outside the allowlist are dropped
261261* **Plan-mode upgrades**: on the Anthropic API and Claude Platform on AWS, an upgrade such as [`opusplan`](#opusplan-model-setting) to an excluded model uses the newest permitted version of the upgrade family. On providers with provider-specific model IDs, and when no version is permitted, the upgrade is skipped and planning continues on the session's model
262262* **[Automatic model fallback](#automatic-model-fallback)**: a fallback whose target is excluded does not run, so the flagged request ends with a refusal instead
263* **[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 provider's default Opus model without consulting the allowlist. Requires Claude Code v2.1.210 or later
263* **[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
264264* **[Fast mode](/docs/en/fast-mode)**: enabling fast mode is refused when the model the session would run on afterward is outside the allowlist
265265
266266```json theme={null}
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