Haiku 5.5 Launches, Breaking Old Code
Anthropic released Claude Haiku 5.5 with 1M context and adaptive thinking, but it breaks compatibility with code written for Haiku 4.5 due to new default behaviors.
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Anthropic launched Claude Haiku 5.5 on October 7, targeting high-volume and latency-sensitive workloads.
The model features a 1 million token context window, 128k max output tokens, and enables 'adaptive thinking' by default. Requests that previously used manual budget_tokens for extended thinking now return a 400 error, and responses may begin with thinking blocks, altering parsing logic.
Production environments currently running Claude Haiku 4.5 face potential breakage if switched directly. Developers must consult the official migration guide to adjust request parameters for the new defaults.