Claude Haiku 5.5 ships at $0.10 input, tenth of Haiku 4.5

Haiku 5.5 arrives almost exactly a year after Haiku 4.5 (October 15, 2025) and completes the 5.5 generation, following Opus 5.5 on September 22 and Sonnet 5.5 on September 28. Anthropic bills it as its cheapest, fastest and smartest small model, and the pricing table backs the cheap part: $0.10 input for prompts up to 100K tokens is one-twentieth of Sonnet 5.5's $2.00. The same announcement also halved Sonnet 5.5's cache-read price from $0.20 to $0.10, which Anthropic says cuts Sonnet 5.5 costs by about 20% on most agentic tasks — a saving that reaches teams who never touch Haiku.

The migration story is where the release gets sharp. Because adaptive thinking is on by default and temperature, top_p, top_k and assistant prefill now trigger 400 errors, a model-ID swap is no longer sufficient. The author's own stock-screening tool RakuScan illustrates the trap: it reads response.content[0].text, which was always a text block under Haiku 4.5 but may now be a thinking block with no .text attribute. The resulting AttributeError slips past handlers that only catch Anthropic SDK errors, and the caller has no try block around it, so a fallback notification path never runs — the failure surfaces the next morning as a missing alert.