Claude Opus 5.5 fast mode is now open to all API users

Anthropic has taken fast mode for Claude Opus 5.5 out of research preview, according to the Claude Platform release notes for October 15, 2026. Fast mode makes the model generate output tokens much faster at a premium price, and until now customers had to request access to use it.

Developers no longer need to send the old fast-mode beta header with Opus 5.5 requests, although requests that still include it will keep working. Opus 5.5 now comes with a default fast mode rate limit on the Start, Build and Scale usage tiers, and fast mode for the model is also available through Claude in Microsoft Foundry for deployments hosted on Azure. Fast mode for the older Claude Opus 5 and Claude Opus 4.8 models stays in research preview, so those requests still need the beta header.

The change follows another developer update a day earlier. On October 14, Anthropic launched OpenTelemetry export in beta, which lets teams trace Messages API calls and Claude Managed Agents sessions in their own monitoring tools. The Claude SDKs now emit trace spans in Python, TypeScript, C#, Go, Java, PHP and Ruby, and API-side spans can be sent to a destination set up in the Claude Console.

Why it matters

Faster output from a top model, plus standard tracing, makes it more practical to put Claude into interactive and closely monitored production apps.

Source: Claude Platform