Claude Sonnet 4.6 launched on AI Gateway on February 17, 2026. Anthropic described it as approaching Opus-level intelligence. The model advances multiple capabilities the Sonnet tier developed across the 4.x generation: stronger agentic coding, improved code review, better frontend UI quality, and higher computer use accuracy.
Two architecture features define Sonnet 4.6. First, adaptive thinking: the model decides when and how much to reason, rather than requiring a fixed extended thinking budget. Simpler requests get a proportionate response. Complex ones receive deeper reasoning automatically. You don't need to categorize each request in advance. This evolves the thinking mode introduced in Claude 3.7 Sonnet into a smarter, model-directed form.
Second, a 1M-token context window at Sonnet pricing. Claude Sonnet 4.5 was the first Sonnet-tier model to reach 1M tokens; Sonnet 4.6 keeps that as standard. For teams working with large codebases, long document collections, or extended agent histories, Opus-approaching quality at 1M tokens and Sonnet pricing changes what's economically feasible.
MCP (Model Context Protocol) support for scaled tool use means Sonnet 4.6 can participate in large tool ecosystems without specifying individual tools for each interaction. The model proactively executes tasks, delegates to subagents, and parallelizes tool calls.