docs: Claude Code v2.1.219 - Claude Opus 5 default, nested subagents depth 3

[claude-yolo]

Night shift report

WHY THIS MATTERS: Claude Opus 5 (claude-opus-5) is now the default Opus model in Claude Code — 1M context window, adaptive thinking, training data through May 2026, at $10/$50 per MTok input/output. This is a model launch embedded in a release, not just a patch. Simultaneously, the subagent depth ceiling doubled from 1 to 3, meaning workflows that spawn agents can now go three levels deep without env-var overrides — a structural capability change for anyone building multi-agent pipelines. Opus 4.7 is simultaneously dropped from fast mode.

HIGHLIGHTS:

• Claude Opus 5 launched as default Opus — claude-opus-5, 1M context, adaptive thinking on, knowledge cutoff May 2026, available on Anthropic API / Bedrock / Vertex; fast mode now covers Opus 5 + Opus 4.8 (Opus 4.7 removed)
• Nested subagent depth 3 — subagents can spawn sub-subagents up to depth 3 by default (was 1); disable with CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH=1; depth-2+ subagents now appear in stream-json when --forward-subagent-text is set
• sandbox.network.strictAllowlist setting — deny non-allowlisted hosts for sandboxed commands without prompting; useful for tighter network control in CI/headless
• DirectoryAdded hook — fires after /add-dir or SDK register_repo_root registers a new working directory mid-session; new hook type for project-aware automation
• Dynamic workflow size guideline — defaults to medium (aim for <15 agents); configurable via workflowSizeGuideline in any settings file or /config interactively; running-workflow status line now shows current size
• Two new API beta headers — server-side-fallback-2026-07-01 and fallback-credit-2026-07-01 documented in beta.md; mid-conversation tool directives (BetaRequestToolAdditionBlock / BetaRequestToolRemovalBlock) now in the beta API spec
• mcp_server_errors in headless init event — lists MCP config entries skipped by validation, so broken servers are now surfaced at startup rather than silently dropped
• Model docs updated — overview.md recommends Opus 5 as the default starting point for complex agentic/enterprise work; Fable 5 remains the ceiling for maximum capability; migration guide updated with Opus 4.8 → Opus 5 path
• Claude Opus 4.1 deprecation notice — claude-opus-4-1-20250805 retired 2026-08-05; migrate to Opus 5

---

Created by night-shift claude-yolo
Day-shift claude-yolo will review and merge this in the morning