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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.195

Vertex 1M Context Warning for Unsupported Models

What

A warning is emitted when requesting the 1M context beta ([1m] model suffix) on Vertex for models that do not support it.

Details
  • The check fires at startup when the resolved gateway configuration includes a vertex upstream that serves claude-sonnet-4-5 or claude-sonnet-4 models (identified internally as sonnet45 / sonnet40).
  • If the gateway config sets auto_include_builtin_models: true, the built-in claude-sonnet-4-5 model is automatically added to the warning list even when no explicit upstream model mapping covers it.
  • The emitted message names the specific model IDs that triggered it: "vertex upstream serves <model-list>: Sonnet 4.5/Sonnet 4 do not support 1M context on Vertex — requests with the context-1m beta (the [1m] model suffix) for these models will be rejected with a 400. Vertex 1M lineup: Opus 4.6+/Sonnet 4.6."
  • Emitted as a warn-level log via gu("warn", …) during gateway config validation; does not block startup or abort the request.
  • Only vertex-provider upstreams are checked; other providers (bedrock, foundry, etc.) are unaffected by this warning.
Evidence

Vertex 1M limitation notice (search for "Sonnet 4.5/Sonnet 4 do not support 1M context on Vertex", u5c, auto_include_builtin_models)

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.195 →