[Feature Request] Allow subagents to override reasoning effort in CustomAgentConfig (parity with Claude Agent SDK)

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
64/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Quiet
Tech stack
typescript, yaml
Domain
developer-experience, tooling

Research direction

Start with CustomAgentConfig in types.d.ts around lines 802–833, then trace how session-level reasoningEffort in providerOptions reaches custom subagent dispatches. Read the YAML frontmatter loader and related github/copilot-cli#2904 context. Done means the config and YAML surfaces accept the documented effort values and omitted values retain the session setting.

Written by the indexing model from the issue text.

Description

enhancement

Summary

Allow custom subagents defined via CustomAgentConfig to specify their own reasoning effort independent of the orchestrator session's reasoning. The Claude Agent SDK supports this via an effort field on AgentDefinition. copilot-sdk's CustomAgentConfig does not, so reasoning is fixed at session level and applies uniformly to every subagent invocation.

Motivation

  • Orchestrators often benefit from high or max reasoning for planning and delegation
  • Many subagent tasks are mechanical execution (validation, extraction, format conversion) and do not benefit from deep reasoning, but today pay its latency and cost
  • Conversely, security focused or analysis focused subagents may want stronger reasoning than the orchestrator
  • Without per subagent control, the tallest reasoning setting propagates to every dispatch

Current state

  • CustomAgentConfig (copilot-sdk types.d.ts, lines 802 to 833) has no reasoningEffort or effort field
  • Session level reasoningEffort in providerOptions applies to all subagent dispatches in that session

Proposed

  1. Add optional reasoningEffort (or effort) field to CustomAgentConfig
  2. Accept existing values: low | medium | high | xhigh | max, plus numeric for models that support it
  3. Fall back to session reasoning when omitted
  4. Mirror the field in the YAML frontmatter loader (coordinated with github/copilot-cli#2904)

Precedent

Claude Agent SDK's AgentDefinition.effort:
https://code.claude.com/docs/en/agent-sdk/subagents

Identical value vocabulary already in use by this SDK.

Related

  • github/copilot-cli#2904 — Custom Agent YAML Frontmatter Should Support Reasoning Effort (CLI surface for the same feature)
  • #1019 — Per agent tool visibility for custom sub agents (same architectural axis)
Dominant language
Java
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Merged PRs (30d)
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