POST /v1/messages
{ "model": "claude-opus-5-5", "thinking": { "type": "disabled" } }
→ HTTP 400 (invalid_request_error)
Fix:
Opus 5.5 (claude-opus-5-5): thinking is always on. thinking: {"type": "disabled"} and thinking: {"type": "enabled", ...} both return 400 — remove the thinking field entirely and set depth with effort. Two more 400s on the same model: tool_choice types any and tool (use auto with strict tool use), and on the Claude API and Google Cloud the older computer_20251124 tool (use computer_toolset_20260801; Bedrock still accepts the old one).
Opus 5 (claude-opus-5): disabling thinking is only accepted at effort high or below. Drop to high/medium/low, or keep xhigh/max and remove the thinking block (Opus 5 thinks by default).