Opus 5.5 cuts price but breaks four Claude agent API patterns
Anthropic’s Opus 5.5 is cheaper than Opus 5, but its migration guide flags four breaking changes—always-on thinking, no forced tool_choice, append-only thinking blocks, and a new computer-use toolset—that can return 400s in existing agent loops. Claude Code and Managed Agents already handle it; custom agents need code changes before flipping the model ID.
