Claude Code v2.1.172: Sub-Agents Now 5 Levels Deep, Bedrock Region Fixes, and Performance Gains

Anthropic shipped Claude Code v2.1.172 with a major change to agent nesting: sub-agents can now spawn their own sub-agents up to 5 levels deep. Previously limited to a single level, this opens up hierarchical task decomposition for complex workflows.

Key Changes

• Sub-agent spawning: agents can now spawn sub-agents recursively (max depth 5).
• Bedrock region fix: AWS_REGION not set? Amazon Bedrock now reads region from ~/.aws/config, matching AWS SDK precedence. Run /status to see where the region came from.
• Plugin search: added a search bar when browsing marketplace plugins via /plugin.
• OTEL metric: claude_code.lines_of_code.count now includes a model attribute.
• 1M context stall fix: sessions using 1M context without usage credits no longer get permanently stuck. The session now automatically compacts back under the standard context limit.
• Performance: reduced redundant message normalization and avoided full history transforms when streaming tool-use state is unchanged. Idle CPU usage dropped — the /goal status chip no longer re-renders at 5 Hz while idle, and fewer UI re-renders occur when sub-agents run in parallel.
• Chrome tool loading: browser tools now load in a single batched call instead of one per tool.
• Permission wildcards fixed: WebFetch(domain:*.example.com) now matches subdomains in allow, deny, and ask rules. File permission rules with mid-pattern wildcards (e.g., Read(secrets-*/config.json)) are no longer rejected at startup.
• /model picker fixes: availableModels restrictions now apply correctly to subagent model overrides, the dispatch model picker, and the advisor model. Version-specific model IDs like claude-opus-4-8 no longer hide the 1M context rows.
• VSCode: PowerShell tool calls now render as proper command displays instead of raw JSON. ANSI escape codes stripped from shell output.
• Other: fixed memory recall for CLAUDE_MEMORY_STORES in remote sessions, fixed workflow validation false positives on Date.now()/Math.random() in comments, and disabled mouse tracking on unsupported Windows consoles.

Who Benefits

This release is for Claude Code users building multi-step agentic workflows, especially those hitting context limits or managing complex sub-task delegation. The nesting change alone is a major unlock for CI pipelines and multi-step refactoring.