Sub-Agents

Sub-agents let you run background tasks without blocking the main conversation. When you spawn a sub-agent, it runs in its own isolated session, does its work, and announces the result back to the chat when finished.

Use cases:

• Research a topic while the main agent continues answering questions
• Run multiple long tasks in parallel (web scraping, code analysis, file processing)
• Delegate tasks to specialized agents in a multi-agent setup

Quick Start

The simplest way to use sub-agents is to ask your agent naturally:

"Spawn a sub-agent to research the latest Node.js release notes"

The agent will call the sessions_spawn tool behind the scenes. When the sub-agent finishes, it announces its findings back into your chat.

You can also be explicit about options:

"Spawn a sub-agent to analyze the server logs from today. Use gpt-5.2 and set a 5-minute timeout."

How It Works

Configuration

Sub-agents work out of the box with no configuration. Defaults:

• Model: target agent’s normal model selection (unless subagents.model is set)
• Thinking: no sub-agent override (unless subagents.thinking is set)
• Max concurrent: 8
• Auto-archive: after 60 minutes

Setting a Default Model

Use a cheaper model for sub-agents to save on token costs:

{
  agents: {
    defaults: {
      subagents: {
        model: "minimax/MiniMax-M2.1",
      },
    },
  },
}

Setting a Default Thinking Level

{
  agents: {
    defaults: {
      subagents: {
        thinking: "low",
      },
    },
  },
}

Per-Agent Overrides

In a multi-agent setup, you can set sub-agent defaults per agent:

{
  agents: {
    list: [
      {
        id: "researcher",
        subagents: {
          model: "anthropic/claude-sonnet-4",
        },
      },
      {
        id: "assistant",
        subagents: {
          model: "minimax/MiniMax-M2.1",
        },
      },
    ],
  },
}

Concurrency

Control how many sub-agents can run at the same time:

{
  agents: {
    defaults: {
      subagents: {
        maxConcurrent: 4, // default: 8
      },
    },
  },
}

Sub-agents use a dedicated queue lane (subagent) separate from the main agent queue, so sub-agent runs don't block inbound replies.

Auto-Archive

Sub-agent sessions are automatically archived after a configurable period:

{
  agents: {
    defaults: {
      subagents: {
        archiveAfterMinutes: 120, // default: 60
      },
    },
  },
}

The sessions_spawn Tool

This is the tool the agent calls to create sub-agents.

Parameters

Model Resolution Order

The sub-agent model is resolved in this order (first match wins):

1. Explicit model parameter in the sessions_spawn call
2. Per-agent config: agents.list[].subagents.model
3. Global default: agents.defaults.subagents.model
4. Target agent’s normal model resolution for that new session

Thinking level is resolved in this order:

1. Explicit thinking parameter in the sessions_spawn call
2. Per-agent config: agents.list[].subagents.thinking
3. Global default: agents.defaults.subagents.thinking
4. Otherwise no sub-agent-specific thinking override is applied

Cross-Agent Spawning

By default, sub-agents can only spawn under their own agent id. To allow an agent to spawn sub-agents under other agent ids:

{
  agents: {
    list: [
      {
        id: "orchestrator",
        subagents: {
          allowAgents: ["researcher", "coder"], // or ["*"] to allow any
        },
      },
    ],
  },
}

Managing Sub-Agents (/subagents)

Use the /subagents slash command to inspect and control sub-agent runs for the current session:

You can reference sub-agents by list index (1, 2), run id prefix, full session key, or last.

```
🧭 Subagents (current session)
Active: 1 · Done: 2
1) ✅ · research logs · 2m31s · run a1b2c3d4 · agent:main:subagent:...
2) ✅ · check deps · 45s · run e5f6g7h8 · agent:main:subagent:...
3) 🔄 · deploy staging · 1m12s · run i9j0k1l2 · agent:main:subagent:...
```

```
/subagents stop 3
```

```
⚙️ Stop requested for deploy staging.
```

```
ℹ️ Subagent info
Status: ✅
Label: research logs
Task: Research the latest server error logs and summarize findings
Run: a1b2c3d4-...
Session: agent:main:subagent:...
Runtime: 2m31s
Cleanup: keep
Outcome: ok
```

Shows the last 10 messages from the sub-agent's transcript. Add `tools` to include tool call messages:

```
/subagents log 1 10 tools
```

Sends a message into the running sub-agent's session and waits up to 30 seconds for a reply.

Announce (How Results Come Back)

When a sub-agent finishes, it goes through an announce step:

1. The sub-agent's final reply is captured
2. A summary message is sent to the main agent's session with the result, status, and stats
3. The main agent posts a natural-language summary to your chat

Announce replies preserve thread/topic routing when available (Slack threads, Telegram topics, Matrix threads).

Announce Stats

Each announce includes a stats line with:

• Runtime duration
• Token usage (input/output/total)
• Estimated cost (when model pricing is configured via models.providers.*.models[].cost)
• Session key, session id, and transcript path

Announce Status

The announce message includes a status derived from the runtime outcome (not from model output):

• successful completion (ok) — task completed normally
• error — task failed (error details in notes)
• timeout — task exceeded runTimeoutSeconds
• unknown — status could not be determined

Tool Policy

By default, sub-agents get all tools except a set of denied tools that are unsafe or unnecessary for background tasks:

Customizing Sub-Agent Tools

You can further restrict sub-agent tools:

{
  tools: {
    subagents: {
      tools: {
        // deny always wins over allow
        deny: ["browser", "firecrawl"],
      },
    },
  },
}

To restrict sub-agents to only specific tools:

{
  tools: {
    subagents: {
      tools: {
        allow: ["read", "exec", "process", "write", "edit", "apply_patch"],
        // deny still wins if set
      },
    },
  },
}

Authentication

Sub-agent auth is resolved by agent id, not by session type:

• The auth store is loaded from the target agent's agentDir
• The main agent's auth profiles are merged in as a fallback (agent profiles win on conflicts)
• The merge is additive — main profiles are always available as fallbacks

Context and System Prompt

Sub-agents receive a reduced system prompt compared to the main agent:

• Included: Tooling, Workspace, Runtime sections, plus AGENTS.md and TOOLS.md
• Not included: SOUL.md, IDENTITY.md, USER.md, HEARTBEAT.md, BOOTSTRAP.md

The sub-agent also receives a task-focused system prompt that instructs it to stay focused on the assigned task, complete it, and not act as the main agent.

Stopping Sub-Agents

Full Configuration Example

Limitations

See Also

• Session Tools — details on sessions_spawn and other session tools
• Multi-Agent Sandbox and Tools — per-agent tool restrictions and sandboxing
• Configuration — agents.defaults.subagents reference
• Queue — how the subagent lane works