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Claude Code v2.1.216 → v2.1.217: subagent concurrency now capped — agentic workflows may silently break #463

Description

@claude-yolo

WHY users should care

Two default behavior changes that could silently break existing agentic workflows:

  • Subagents now capped at 20 concurrent by default — previously unbounded. Set CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS to override.
  • Nested subagent spawning disabled by default — subagents no longer spawn child subagents unless CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH is set.

If you have workflows that fan out lots of background agents or use multi-level agent hierarchies, test before upgrading.

Other notable changes

  • iOS Simulator pane is now first-class in Desktop (no computer use needed)
  • Search results with citations are GA — no more beta header required (except Haiku 3)
  • MCP memory leak fixed — truncated tool outputs were holding full results in memory for the entire session
  • Corporate mTLS/proxy/OAuth settings now apply in Claude Desktop — were silently ignored before
  • Windows auto-update fixed — failed updates no longer nuke claude.exe
  • CLAUDE.md brace expansion now budget-bounded — pathological brace groups could OOM at startup
  • --max-budget-usd now enforces on background subagents
  • Desktop preview url field — open preview at specific HTTPS localhost address
  • Managed Agents SDK: TypeScript, Go, C#, Java, PHP, Ruby examples added

Source

PR: https://github.com/anthropics/claude-code-docs/pull/1080


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