Effective harnesses for long-running agents
Anthropic's fix for agents that lose track across context windows is an initializer agent plus a coding agent that leaves artifacts for the next session.
Compaction alone was not enough, since even Opus 4.5 running in a loop on the Agent SDK across context windows fell short of a production-quality app. The two-agent harness sets up the environment once, then makes incremental progress each session and documents state, like engineers handing over shifts.
- Date
- Wednesday, 26 November 2025
- Lab
- Anthropic
- Kind
- paper
- Access
- paper only
Qualitative engineering guidance with a code quickstart; no benchmark was read. Continued in 'Harness design for long-running application development' (2026-03-24).
Sources
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