Claude Sonnet model releases

A source-backed timeline for the Claude Sonnet model family, collecting release dates, labs, access details, context windows, and major lifecycle changes.

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Sep 29, 2025

Claude Sonnet 4.5

Anthropic

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Claude Sonnet 4.5

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AnthropicFrontierProprietary

Anthropic's September 2025 Sonnet release, positioned as its strongest model for coding, agents, and computer-use workflows at launch. Proprietary API model with text, vision, and code capabilities, 200K context, and Sonnet-tier list pricing.

—Undisc.200K ctxSep 29, 2025