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Sweep 22 Oct 2026 · 21:04Z Build v2.1.309 528 read Stable v2.1.308 Latest v2.1.309 Next v2.1.309 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.0.59 ·

Main Thread Agent Definition Support

Entry
JSON All of v2.0.59
EntryKind: in v2.0.59,
ChangesSection of the release

What: New architecture allowing main thread agents to provide custom system prompts.

Details:

  • New mainThreadAgentDefinition parameter added to main UI component at line 480951
  • HJ9() helper function at line 480920 handles system prompt resolution
  • Conditionally calls agent's getSystemPrompt() method with tool context
  • Enables more flexible agent customization
  • Evidence: 7 occurrences in v2.0.59, zero in v2.0.58

See this entry in the whole of v2.0.59 →

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