Anthropic releases Claude Sonnet 4.5

Anthropic released Claude Sonnet 4.5 on 29 September 2025 at the same price as Sonnet 4, $3 and $15 per million input and output tokens. The company said it could hold a single coding task for about 30 hours without help, against roughly 7 hours for Claude Opus 4.

Why it mattered Sustained autonomous operation was the clearest capability measure in agentic coding, the product category that had come to define competition between the laboratories.