Sub-Agents Are Just Wrong
13 hours ago
- Polylane replaced a multi-sub-agent workflow (triage, coordinator, hypothesis investigators, coding agent) with a single agent handling the entire process from triage to pull request.
- The sub-agent architecture suffered from context loss between agents due to summarization, expensive operation, difficult debugging, and poor pull request quality focusing on symptoms rather than root causes.
- Switching to a single agent eliminated context loss, reduced median time from issue detection to pull request from 2.2 hours to 35 minutes, and p90 from nine days to under two hours.
- The percentage of detected issues resulting in a pull request rose from 0.6% (sub-agents) to 4.2% (single agent), and cost per pull request dropped from $111 to about $18.
- Key lessons: handoffs lose context, evaluate the whole run not individual agents, and keep a single trace per run for easier debugging.