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fix: Claude Sonnet 5.5 support for claude_code and anthropic providers - #3947
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Registers `claude-sonnet-5-5` (released 2026-09-28) with a 1M context
window in the `claude_code` provider list.
Unlike Opus 5.5, Sonnet 5.5 is NOT correctly classified by the existing
predicates: `contains("sonnet-5")` puts it in `AdaptiveFriendly`, which
would forward `budget_tokens` and non-default sampling params (both
return 400 on Sonnet 5.5) and rewrite `xhigh` to `max` even though
Sonnet 5.5 supports `xhigh` natively.
- `ModelSpecificReasoning` now matches `sonnet-5-5` as `AdaptiveOnly`,
ahead of the broader `sonnet-5` check.
- `interleaved_thinking_required` returns false for `sonnet-5-5`, since
adaptive thinking auto-enables interleaving.
- `get_context_length` already returns 1M via the `claude-sonnet-5`
prefix; a regression test locks that in.
A guard test ensures plain Sonnet 5 stays `AdaptiveFriendly`.
Co-Authored-By: ForgeCode <[email protected]>
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What
Registers
claude-sonnet-5-5(released 2026-09-28) as a selectable model. It follows #3928 (Opus 5.5).Why
Sonnet 5.5 is the new Sonnet in the Claude 5.5 family: 1M context, 128K max output, $2/$10 per MTok (same price as Sonnet 5). Anthropic reports it is 30%+ faster than Sonnet 5.
Changes
provider.json: addsclaude-sonnet-5-5to theclaude_codeprovider list, the same scope as #3928. Theanthropicprovider gets its model list from the API at runtime.Unlike Opus 5.5, this one needs a logic fix.
ModelSpecificReasoning::familymatchescontains("sonnet-5"), which putsclaude-sonnet-5-5inAdaptiveFriendly. According to the Sonnet 5.5 migration guide, that family is wrong for this model in three ways:AdaptiveFriendlybehaviourreasoning.max_tokensasthinking.type: enabled+budget_tokens"thinking.type.enabled" is not supported for this modeltemperature/top_p/top_kxhigheffort tomaxxhighnativelymodel_specific_reasoning.rsfamily()sonnet-5-5is now matched asAdaptiveOnly, before the broadersonnet-5checkanthropic.rsinterleaved_thinking_requiredfalseforsonnet-5-5, since adaptive thinking enables interleaving on its ownresponse.rsget_context_lengthstarts_with("claude-sonnet-5")already returns 1MTests
test_sonnet_5_5_drops_max_tokens_and_sampling_params: coversclaude-sonnet-5-5and the Bedrock-styleanthropic.claude-sonnet-5-5;xhighis preservedtest_sonnet_5_remains_adaptive_friendly: checks that plain Sonnet 5 keeps its current behaviour, so the predicate ordering can't regresstest_get_context_length_sonnet_5_5claude-sonnet-5-5added to the no-interleaved-thinking header test matrixcargo test -p forge_app -p forge_repo: 1060 passed, 0 failed.cargo clippy --all-targets: clean.Notes for reviewers
tool_choiceany/tool, the same as Opus 5.5 (flagged in fix: Claude Opus 5.5 support for claude_code and anthropic providers #3928). Nothing in the agent loop sends those today, so this PR leaves them alone.thinking: disabled: Sonnet 5.5 rejects it and wantsbetween_toolsinstead.Thinking::Disabledis never built outside tests, so nothing breaks today. It matters if a "thinking off" mode is added later.interleaved_thinking_requiredlists Sonnet 5, but the predicate has nosonnet-5match, so Sonnet 5 still gets the interleaved beta header. I didn't change it, because that would alter Sonnet 5's behaviour outside this PR's scope. Mentioning it in case it's unintended.bedrock,vertex_ai_anthropicandopencode_zen. Following fix: Claude Opus 5.5 support for claude_code and anthropic providers #3928, this PR only addsclaude_code. Happy to add the others in a follow-up once the per-platform IDs are confirmed.Co-Authored-By: ForgeCode [email protected]