Extremelly slow subagent searching

[CaioDGallo]

For the subagent tasks that the agent spins up in the conversation, it is agonizingly slow compared to the regular main agent doing the same type of task. Happens every time a subagent is spawned.

[adboio]

when you say the session is dying, are you referring to the entire posthog code agent session, or specifically the sub-agents dying?

i'm investigating an issue right now where sub-agents are constantly taking forever and then failing -- usually the primary agent says something like "the sub-agents ran out of context. let me search directly" -- and wondering if this is related at all

[adboio]

claude says

That's the smoking gun for slowness. getDefaultSubagentModel() returns 'inherit' — so general-purpose sub-agents run on Opus 4.6, the same as the parent. That's why they're agonizingly slow.

which would also maybe explain running out of context.... not sure if i buy it yet, but testing some things now to verify

[CaioDGallo]

@adboio The "session diying" issue I mentioned was fixed after Jonathan's auth changes, I updated the main issue.

But what I mean is that it literally looks like the subagent is slower to read files, grep files, "think" about what it just ingested. I have never run out of context on subagents because it would take more than an hour to do so, probably, in the scenarios I tested.

In this example below first subagent took 14m, second 9m, and when I ran the same thing on main agent it spent 3m to finish the researching and implementation all together, it was not a complex research of any kind.

[adboio]

added some logs, very weird things are happening with the subagent context/usage... the very first turn in the subagent session has only 3 input tokens, 1 output token, and 180k cached read tokens

{
  "type": "notification",
  "timestamp": "2026-04-02T17:33:36.576Z",
  "notification": {
    "jsonrpc": "2.0",
    "method": "_posthog/subagent_usage_update",
    "params": {
      "sessionId": "019d4f41-b6ce-74ee-b993-b2dfe308e87f",
      "parentToolCallId": "toolu_01AUwRMeCPoEqyQqRRwiUZjs",
      "inputTokens": 3,
      "outputTokens": 1,
      "cachedReadTokens": 180880,
      "cachedWriteTokens": 5684
    }
  }
}
{
  "type": "notification",
  "timestamp": "2026-04-02T17:33:36.820Z",
  "notification": {
    "jsonrpc": "2.0",
    "method": "_posthog/subagent_usage_update",
    "params": {
      "sessionId": "019d4f41-b6ce-74ee-b993-b2dfe308e87f",
      "parentToolCallId": "toolu_01AUwRMeCPoEqyQqRRwiUZjs",
      "inputTokens": 3,
      "outputTokens": 1,
      "cachedReadTokens": 180880,
      "cachedWriteTokens": 5684
    }
  }
}
{
  "type": "notification",
  "timestamp": "2026-04-02T17:33:36.992Z",
  "notification": {
    "jsonrpc": "2.0",
    "method": "_posthog/subagent_usage_update",
    "params": {
      "sessionId": "019d4f41-b6ce-74ee-b993-b2dfe308e87f",
      "parentToolCallId": "toolu_01AUwRMeCPoEqyQqRRwiUZjs",
      "inputTokens": 3,
      "outputTokens": 1,
      "cachedReadTokens": 180880,
      "cachedWriteTokens": 5684
    }
  }
}
{
  "type": "notification",
  "timestamp": "2026-04-02T17:33:58.481Z",
  "notification": {
    "jsonrpc": "2.0",
    "method": "_posthog/subagent_usage_update",
    "params": {
      "sessionId": "019d4f41-b6ce-74ee-b993-b2dfe308e87f",
      "parentToolCallId": "toolu_01AUwRMeCPoEqyQqRRwiUZjs",
      "inputTokens": 3,
      "outputTokens": 1,
      "cachedReadTokens": 181806,
      "cachedWriteTokens": 12851
    }
  }
}
{
  "type": "notification",
  "timestamp": "2026-04-02T17:33:58.733Z",
  "notification": {
    "jsonrpc": "2.0",
    "method": "_posthog/subagent_usage_update",
    "params": {
      "sessionId": "019d4f41-b6ce-74ee-b993-b2dfe308e87f",
      "parentToolCallId": "toolu_01AUwRMeCPoEqyQqRRwiUZjs",
      "inputTokens": 3,
      "outputTokens": 1,
      "cachedReadTokens": 181806,
      "cachedWriteTokens": 12851
    }
  }
}
{
  "type": "notification",
  "timestamp": "2026-04-02T17:33:58.983Z",
  "notification": {
    "jsonrpc": "2.0",
    "method": "_posthog/subagent_usage_update",
    "params": {
      "sessionId": "019d4f41-b6ce-74ee-b993-b2dfe308e87f",
      "parentToolCallId": "toolu_01AUwRMeCPoEqyQqRRwiUZjs",
      "inputTokens": 3,
      "outputTokens": 1,
      "cachedReadTokens": 181806,
      "cachedWriteTokens": 12851
    }
  }
}
{
  "type": "notification",
  "timestamp": "2026-04-02T17:33:59.142Z",
  "notification": {
    "jsonrpc": "2.0",
    "method": "_posthog/subagent_usage_update",
    "params": {
      "sessionId": "019d4f41-b6ce-74ee-b993-b2dfe308e87f",
      "parentToolCallId": "toolu_01AUwRMeCPoEqyQqRRwiUZjs",
      "inputTokens": 3,
      "outputTokens": 1,
      "cachedReadTokens": 181806,
      "cachedWriteTokens": 12851
    }
  }
}

[adboio]

ok looks like they are on haiku, but still 186k tokens on a fresh session (first prompt was "spawn a subagent for ..."

also, recursive subagent spawning?? i think because it passed the prompt in directly, the sub-agent spawned another sub-agent...

also subagentSessionId is the same as parentSessionId, is that expected?

2026-04-02T18:01:38.736Z [ClaudeAcpAgent] [info] Subagent first turn context breakdown {
  "subagentSessionId": "019d4f5b-5aec-7056-9be4-200c39c994ff",
  "parentSessionId": "019d4f5b-5aec-7056-9be4-200c39c994ff",
  "parentToolCallId": "toolu_01EPyd39frs2fof5Y5oAKn8F",
  "totalInputContext": 186559,
  "inputTokens": 3,
  "cachedReadTokens": 0,
  "cachedWriteTokens": 186556,
  "outputTokens": 1,
  "contentBlockCount": 1,
  "contentSummary": [
    {
      "type": "tool_use",
      "name": "Grep",
      "id": "toolu_01QQs4ZrxPr22DWHGjPWDgJr"
    }
  ],
  "model": "claude-haiku-4-5-20251001"
}
2026-04-02T18:01:38.744Z [ClaudeAcpAgent] [info] Subagent transcript message {
  "subagentSessionId": "019d4f5b-5aec-7056-9be4-200c39c994ff",
  "role": "user",
  "blockCount": 1,
  "blocks": [
    {
      "type": "text",
      "charLength": 67,
      "preview": "spawn a subagent to understand how PR URLs are tracked in this repo"
    }
  ]
}
2026-04-02T18:01:38.744Z [ClaudeAcpAgent] [info] Subagent transcript message {
  "subagentSessionId": "019d4f5b-5aec-7056-9be4-200c39c994ff",
  "role": "assistant",
  "blockCount": 1,
  "blocks": [
    {
      "type": "thinking"
    }
  ]
}
2026-04-02T18:01:38.744Z [ClaudeAcpAgent] [info] Subagent transcript message {
  "subagentSessionId": "019d4f5b-5aec-7056-9be4-200c39c994ff",
  "role": "assistant",
  "blockCount": 1,
  "blocks": [
    {
      "type": "tool_use",
      "name": "Agent"
    }
  ]
}