Why did my Claude Haiku calls start 400ing? Three AI API changes that break code quietly

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Why did my Claude Haiku calls start 400ing? Three AI API changes that break code quietly

Three AI API changes from the last two weeks that quietly break shipped code: Claude Haiku 5.5 migration 400s, Managed Agents web_fetch gating, and the GPT-6 plan split.

Three AI API changes from the last two weeks that quietly break shipped code: Claude Haiku 5.5 migration 400s, Managed Agents web_fetch gating, and the GPT-6 plan split.