the diff / October 8, 2026 / Claude API

Claude Haiku 5.5 is out. Code written for Haiku 4.5 can break

score more tokens, same text: 30%

Anthropic launched claude-haiku-5-5 on October 7 at $0.10 in and $0.50 out per Mtok under 100K tokens. Haiku 4.5 thinking budgets now return a 400 error.

official source: platform.claude.com →

What changed

On October 7 Anthropic released Claude Haiku 5.5, model id claude-haiku-5-5: 1M token context, 128k max output, adaptive thinking on by default. Prompts up to 100,000 tokens cost $0.10 per million input tokens and $0.50 output. Over that, $0.50 and $2.50. Haiku 4.5 is $1 and $5. Claude Code 2.1.293 makes it the default Haiku. Code written for Haiku 4.5 can break: budget_tokens, temperature, top_p, top_k and assistant prefill now return a 400 error, and the same text counts as about 30% more tokens.

Why it matters if you ship with an agent

Do not just swap the id. Grep for budget_tokens, temperature and top_p next to any haiku model string. Recount prompts and raise max_tokens values tuned for 4.5, since thinking tokens count against them. Pick content blocks by type, not position. Prompts over 100K tokens pay five times the rate. Claude Code's /claude-api migrate runs Anthropic's ten-step guide for you. Read what it changes.

Source: https://platform.claude.com/docs/en/release-notes/overview

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The Diff is Accept All's short note on changes that alter how you ship with an agent. Older: Lovable drops Gemini 3.6 Flash on November 19.