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Covered in AI Engineering, where the background and the sources for this subject live.
Claude cache diagnostics compares the current request with the response `id` of the previous diagnosed turn and reports the first divergence across model, system, tools, or messages. Since 23 September 2026 the `diagnostics` field is always present, so reliable debugging means reading that field together with `usage.cache_read_input_tokens`.
4 min read
Anthropic's mid-conversation-tool-changes-2026-07-01 beta lets a system-role message add or remove already-declared tools partway through a conversation without invalidating the cached prefix above it. LangChain wired this into ChatAnthropic on 23 September 2026, and its wrapper silently drops any other content type from that message with only a logged warning.
5 min read
Claude Opus 5.5 launched September 22, 2026 with four breaking changes that return a 400 error: disabled thinking, forced tool_choice, computer_20251124 on the API and Google Cloud, and replayed thinking blocks on newer accounts. A fifth change returns 200: tool-call progress text goes quiet by default, and the effort parameter's default silently drops from high to medium.
5 min read