What's new in Claude Sonnet 5
- ID
- 2187
- Status
- summarized
- Published
- 01 Jul 2026, 5:23 AM
- Fetched
- 01 Jul 2026, 6:02 AM
- Provider
- Simon Willison
- Category
- developer-ai
- Original URL
- https://simonwillison.net/2026/Jun/30/claude-sonnet-5/
- Source URL
- https://simonwillison.net/atom/everything/
Summary
- Score
- 7.5
- Created
- 01 Jul 2026, 6:02 AM
- Tags
- Audience
- developersai/ml learnersai agent users
What happened
Claude Sonnet 5 released with near-Opus 4.8 performance at a lower API price, but uses a new tokenizer averaging 30% more tokens for English text—effectively a net price increase. Key API changes include a 128K output limit, 1M context window, removal of temperature/top-p/top-k, and adaptive thinking on by default.
Why it matters
Budget-sensitive developers must recalculate real costs; default "thinking" mode and missing sampling params change prompt engineering and output determinism patterns.
Discussion angle
What does the 30% token swell mean for your current LLM pipelines and per-request budget, and will you adopt the $2 introductory pricing before the August deadline?