fix(provider): scope thinking binding to Claude 5.1+ - #46848
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Issue for this PR
Fixes #46729
Fixes #46777
Type of change
What does this PR do?
Stop automatically adding thinking block binding to Claude 4.x and 5.0 requests. Those models do not need the prefix-mismatch control, and some deployments reject it. This also affects Haiku 4.5 title generation even when the main Opus 5 request succeeds.
Use Claude 5.1+ as the forward-compatible default, with an explicit exception for Mythos 5.1. Anthropic documents enforcement on Fable 5.1 and later models, and says Mythos 5.1 does not run the conversation-prefix check: https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-in-conversation
The numeric cutoff is our forward-compatibility policy, not a claim that every future cloud deployment has been verified. Match API model IDs, including Bedrock prefixes, Vertex suffixes, and either family/version order. Preserve existing thinking settings on excluded models and keep binding protection on eligible models.
No opt-out, SDK upgrade, retry change, or API routing change.
How did you verify your code works?
Run from
packages/opencode:bun test test/provider/transform.test.ts test/provider/amazon-bedrock.test.ts --only-failures— 576 passbun typecheck— passesThe new regression cases failed before the implementation change. Coverage includes future versions, the Mythos exception, and SDK request bodies/betas for Opus 5, Sonnet 5, and Haiku title generation across Anthropic, Vertex, and Bedrock. Existing Fable 5.1 wire tests still pass.
These are captured-request tests, not new live-provider verification.
Screenshots / recordings
N/A
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