arXiv cs.CLPaper
Harness Evolution Hits a Ceiling: When Weight Training Should Begin
The insight is structural: harness evolution (prompting, tool-calling, step control) fixes process failures; weight training fixes content failures. For builders extending small models like Qwen 3.5-4B, this means you have a roadmap—run your agent, categorize failure modes, and you'll know whether to iterate on the prompt layer or retrain. The numbers are good: the harness alone took 4B from 0.16 to 0.30 on DeepPlanning, then training kept going from there.