Anthropic releases Claude Sonnet 5.5

On 28 September 2026 Anthropic released Claude Sonnet 5.5 at $2 input and $10 output per million tokens, with 1M-token context and 128K max output. It runs on the Claude Platform, AWS, Google Cloud and Microsoft Foundry, and GitHub added it to Copilot the same day.

Why it mattered Anthropic claimed it runs over 30% faster and up to 30% cheaper per task than Sonnet 5; Artificial Analysis measured about 50% higher cost per task at max effort, making cost-per-task the month’s contested metric.

Anthropic reported 70.6% on Terminal-Bench 4.0 for Sonnet 5.5, against 10.3% for Sonnet 5 and 66.4% for Opus 5.5, with the caveat that Sonnet 5.5 ran at Max effort and Opus 5.5 at Xhigh. The company says it is the first Sonnet model to ship with cyber safeguards, and it is available under the API id claude-sonnet-5-5.