Anthropic released Claude Sonnet 5 on June 30, an update substantially improved over predecessor Claude Sonnet 4.6 in coding, reasoning, tool use, and knowledge work. The model can make plans, use tools like browsers and terminals, and run autonomously at a level that required larger and more expensive models a few months ago. Safety assessments found Sonnet 5 shows an overall lower rate of undesirable behaviors than Sonnet 4.6 and is generally safer to use in agentic contexts. Claude Sonnet 5 is a drop-in upgrade with three behavior changes: adaptive thinking is on by default, manual extended thinking now returns a 400 error, and setting sampling parameters to non-default values also returns a 400 error. Sonnet 5 uses an updated tokenizer to improve performance and offers performance close to Opus 4.8 at lower prices. It is available across all plans, including as the default model for Free and Pro plans, and to Max, Team, and Enterprise users. It is also available in Claude Code and on the Claude Platform, launching with introductory pricing of $2 per million input tokens and $10 per million output tokens through August 31, 2026, after which it will be priced at $3 per million input tokens and $15 per million output tokens. Developers can use Claude Sonnet 5 via the Claude API.