fix: skip extended thinking params for Haiku models#1127
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Haiku models (e.g. claude-haiku-4-5-20251001) do not support extended thinking, but the substring check `"4-5" in model` was matching them and sending `thinking.adaptive.budget_tokens`, causing a 400 error from the Anthropic API. Skip thinking params entirely when the model name contains 'haiku'.
teknium1
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Haiku models don't support extended thinking at all. Without this guard, claude-haiku-4-5-20251001 would receive type=enabled + budget_tokens and return a 400 error. Incorporates the fix from PR #1127 (by frizynn) on top of #1128's adaptive thinking refactor. Verified live with Claude Code OAuth: claude-opus-4-6 → adaptive thinking ✓ claude-haiku-4-5 → no thinking params ✓ claude-sonnet-4 → enabled thinking ✓
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angelburgosrosado
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Apr 27, 2026
Haiku models don't support extended thinking at all. Without this guard, claude-haiku-4-5-20251001 would receive type=enabled + budget_tokens and return a 400 error. Incorporates the fix from PR NousResearch#1127 (by frizynn) on top of NousResearch#1128's adaptive thinking refactor. Verified live with Claude Code OAuth: claude-opus-4-6 → adaptive thinking ✓ claude-haiku-4-5 → no thinking params ✓ claude-sonnet-4 → enabled thinking ✓
02356abc
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May 14, 2026
Haiku models don't support extended thinking at all. Without this guard, claude-haiku-4-5-20251001 would receive type=enabled + budget_tokens and return a 400 error. Incorporates the fix from PR NousResearch#1127 (by frizynn) on top of NousResearch#1128's adaptive thinking refactor. Verified live with Claude Code OAuth: claude-opus-4-6 → adaptive thinking ✓ claude-haiku-4-5 → no thinking params ✓ claude-sonnet-4 → enabled thinking ✓
olympus-terminal
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May 16, 2026
Haiku models don't support extended thinking at all. Without this guard, claude-haiku-4-5-20251001 would receive type=enabled + budget_tokens and return a 400 error. Incorporates the fix from PR NousResearch#1127 (by frizynn) on top of NousResearch#1128's adaptive thinking refactor. Verified live with Claude Code OAuth: claude-opus-4-6 → adaptive thinking ✓ claude-haiku-4-5 → no thinking params ✓ claude-sonnet-4 → enabled thinking ✓
Egavasyug
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Jun 10, 2026
Haiku models don't support extended thinking at all. Without this guard, claude-haiku-4-5-20251001 would receive type=enabled + budget_tokens and return a 400 error. Incorporates the fix from PR NousResearch#1127 (by frizynn) on top of NousResearch#1128's adaptive thinking refactor. Verified live with Claude Code OAuth: claude-opus-4-6 → adaptive thinking ✓ claude-haiku-4-5 → no thinking params ✓ claude-sonnet-4 → enabled thinking ✓
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Summary
Fixes a bug where Haiku models (e.g.
claude-haiku-4-5-20251001) would receive extended thinking parameters, causing a 400 error from the Anthropic API.Bug
The reasoning config logic in
anthropic_adapter.pyuses substring matching to detect model capabilities:This check matches Haiku model names like
claude-haiku-4-5-20251001because they contain the substring"4-5". As a result, the adapter sendsthinking: {type: "adaptive", budget_tokens: ...}to the API — but Haiku models do not support extended thinking at all, so the API returns a 400 error.Root Cause
The substring-based version check does not account for the fact that Haiku models share version substrings (e.g.
4-5) with Sonnet/Opus models that do support thinking.Fix
Added a guard clause to skip thinking parameters entirely when the model name contains
"haiku":This ensures Haiku models are never sent thinking parameters, regardless of version substring matches.
Test plan
claude-haiku-4-5-20251001no longer includethinkingparamsclaude-sonnet-4-5-20250514still getsthinking: {type: "adaptive", ...}thinking: {type: "enabled", ...}