Claude Sonnet 4.6

Claude Sonnet 4.6 (API name claude-sonnet-4-6) is the mid-range Claude that Anthropic released in February 2026 and today lists among its legacy models: still fully available, no longer the recommended default. Its successor, Claude Sonnet 5, arrived on 30 June 2026 and has its own profile here. What makes 4.6 worth a separate entry is that it was the first Sonnet with a one-million-token context window — a capacity previously reserved for the Opus line — while keeping Sonnet pricing at $3 per million input tokens and $15 per million output. That combination is why the model stayed in wide use after its replacement shipped: for long-document and long-session work it is the cheapest million-token Claude Anthropic sells. It also sits on the boundary of a change in how Claude reasons. Sonnet 4.6 supports both the older explicit extended thinking, where a developer sets a thinking budget by hand (Anthropic now marks that mode deprecated), and adaptive thinking, where the model decides for itself how long to deliberate. Later models dropped the manual option entirely. Anthropic's published training data cutoff is January 2026, with knowledge described as most reliable through August 2025. Maximum output is 128,000 tokens per request, and up to 300,000 through the Message Batches API with an extended-output beta header. Anthropic guarantees availability until at least 17 February 2027; no retirement date has been announced.

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