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No. 4 · 19 October 2026

This week in Claude

  1. 4.1
    API · 2026-10-15

    Fast mode is out of preview for Claude Opus 5.5

    You no longer need to request access to fast mode on Claude Opus 5.5, the fast-mode-2026-02-01 beta header is no longer required, and the model now has a default fast mode rate limit in the Start, Build and Scale tiers.

    Try it: If you already send the beta header to Opus 5.5, nothing breaks; keep sending it for Opus 5 and Opus 4.8, where fast mode is still in research preview.

    platform.claude.com ↗
  2. 4.2
    API · 2026-10-14

    OpenTelemetry export for the API and Managed Agents (beta)

    You can now trace Messages API requests and Managed Agents sessions in your own observability tool, and the SDKs in seven languages emit spans.

    Try it: If you run an app on the API, add an OpenTelemetry destination in the Claude Console and read the setup page first.

    platform.claude.com ↗
  3. 4.3
    Claude Code · 2026-10-15

    Claude Code 2.1.297 to 2.1.303: idle compaction and fork sub-agents on by default

    A conversation of 200K+ tokens left idle for about 54 minutes is now compacted before the one-hour prompt cache expires, so your next message doesn't reprocess it all, and fork sub-agents are now on by default in claude -p, the Agent SDK, the desktop app and VS Code.

    Try it: If you'd rather keep long sessions untouched, open /config and switch off the Idle compaction row.

    raw.githubusercontent.com ↗
  4. 4.4
    Designs, slides & docs · 2026-10-15 · act by 14 December 2026

    Standalone Claude Design closes on 14 December 2026

    Claude Code 2.1.302 now tells you in /design-sync and /design-login that standalone Claude Design (claude.ai/design) closes by December 14, 2026.

    Try it: If you keep designs or a design system in claude.ai/design, check what you rely on there before that date.

    raw.githubusercontent.com ↗
  5. 4.5
    Claude app · 2026-10-15

    Claude Desktop gets a session rail, saved environments and nested sessions

    The Code tab in the desktop app (v2.42304.0) now has a rail beside the conversation with cards for environment, context, changes and background tasks, and lets you save a folder, SSH host or cloud environment to pick when you start a session.

    Try it: Start a session, then use "Save as environment" at the top to keep the folder and branch you started in.

    claude.com ↗
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