Four breaking changes in Claude Opus 5.5: thinking can't be disabled, forced tool_choice returns 400, thinking blocks don't cross non-Fable/Mythos models, and computer_20251124 is gone. Each has a specific fix — three carry fallback routing implications the announcement skips.
Two new Claude API betas: `compact-2026-09-04` moves summarization off the critical path into a background call, and the `auto` permission mode shifts tool trust evaluation from your code to the server. Both change how you design stateful agentic loops.
Anthropic's September 1 API release added three beta controls — per-message effort, turn-scoped system messages, and mid-conversation tool changes — that let operators adjust compute intensity and tool sets in long agentic sessions without invalidating the cache prefix.
Anthropic's ant CLI v1.30.0 ships ant apply: declare agents, environments, and deployments as repo files. For gateway operators, the model field now governs routing, and claude-lock.json tracks drift.
Anthropic's June 11 platform update adds response_inclusion to web_search_20260318 and web_fetch_20260318, letting operators drop consumed search result blocks from API responses and cut output token costs in multi-step agentic workflows.
Anthropic's code execution tool now tells Claude about its 90-second per-cell time limit before it writes any code — reducing detection_timeout failures. What changed, which models support it, and the pipeline fixes operators need (including Haiku 4.5 routing gotchas).
