Observed

Source-reviewed: holds for mainstream chat completions; documented divergences at the edges: non-compliant tool-call IDs are not normalized, breaking cross-provider multi-turn tool use (#22317); the thinking.summary field was silently dropped routing Anthropic requests to the OpenAI Responses API (fixed in v1.82.3-stable, TD re-verified present through v1.83.14-stable.patch.3 on 2026-05-17); VertexAI streaming returned the wrong finish_reason for tool calls, looping agents (fixed in v1.82.1+).