GitHub: Claude Opus 4.8 Fast Mode Arrives in Copilot Preview; Anthropic Retires Fast Mode for Opus 4.6

What Does Fast Mode Bring to GitHub Copilot?

GitHub announced on June 29 that Claude Opus 4.8 fast mode — a model variant optimized for faster output token generation while maintaining the intelligence level of standard Claude Opus 4.8 — is entering preview within GitHub Copilot. The service counts more than 15 million users.

Fast mode is not a trade-off between speed and capability. According to the GitHub Changelog, the model delivers “significantly faster output tokens” with “the same level of intelligence as Claude Opus 4.8”. Primary use cases are interactive coding and agentic workflows where responsiveness directly impacts productivity.

The preview is available to Copilot Pro+, Max, Business, and Enterprise subscribers through VS Code, Visual Studio, JetBrains, Xcode, Copilot CLI, and mobile apps. Business and Enterprise administrators must manually enable it in settings — it is off by default.

Anthropic Retires Fast Mode for Opus 4.6

On the same day, Anthropic announced in release notes that fast mode is no longer available on the claude-opus-4-6 model. API requests with the speed: "fast" parameter now automatically execute at standard speed and are billed at the standard price — without error or rejection. The usage.speed field in the response transparently shows the speed actually used.

Two Announcements, One Consolidation

Both announcements together carry one message: fast mode consolidates exclusively on Claude Opus 4.8. Opus 4.6 loses accelerated mode capability, while Opus 4.8 becomes the sole model supporting increased speed — both directly through the Anthropic API, and now through GitHub Copilot.

For developers working in GitHub Copilot, the preview brings faster responses in agentic tasks without sacrificing model capability. For developers calling the Anthropic API directly, the change is unambiguous: speed: "fast" only makes sense with claude-opus-4-8.