Anthropic Releases Claude Sonnet 4.6 with 1 Million Token Context Window

Summary

Anthropic released Claude Sonnet 4.6 on February 17, 2026, a mid-tier model update that brings flagship-adjacent capabilities at unchanged pricing. The release extends the 1 million token context window to the Sonnet tier — previously limited to Opus 4.6 — and introduces an Adaptive Thinking Engine that allows the model to dynamically allocate reasoning effort based on task complexity via a new API parameter. Key capabilities include enhanced computer use (automated UI navigation across Chrome,