Anthropic's Claude platform lists Sonnet 5.5 as released September 28, 2026 and active as its latest Sonnet model. The published model ID is claude-sonnet-5-5. Its model sheet lists a one-million-token context window, a synchronous output limit of 128,000 tokens, and base Claude API rates of $2 per million input tokens and $10 per million output tokens. Anthropic lists the model for its own API and several cloud platforms. These are provider specifications, not an independent benchmark of performance.
GitHub announced on September 28 that Sonnet 5.5 is generally available in GitHub Copilot for Pro, Pro+, Max, Business and Enterprise users. GitHub says rollout is gradual, so an eligible user may not see the model immediately in the picker. It lists access through VS Code, Visual Studio, GitHub Copilot CLI and several other clients. GitHub's early testing says the model matched Sonnet 5 on coding tasks with fewer steps, tokens and tool calls and finished noticeably faster, but GitHub did not quantify a general speed gain in this announcement.
For developers, the new model is not a drop-in replacement in every integration. Anthropic's model documentation describes changes in how thinking is controlled, forced tool use, and the accepted computer-use tool version. Teams maintaining an API integration should read the current migration notes before switching model IDs. No claim of a universal 30 percent speed gain or superiority over Opus is supported by the two sources checked here.