Mixing Agent Roles in AI Metrics Can Manufacture False Model Rankings
A developer running a fleet of coding agents on a single machine discovered that pooling performance metrics across two distinct agent roles — long interactive main threads and short one-shot sub-agents — produced misleading model comparisons. The same model performing the same task showed output token counts differing by up to 135 times depending on which role it occupied. Behavioural metrics like file re-edit rate and error-recovery count were structurally near-zero for sub-agents, meaning almost all meaningful signal existed only in main-thread data. Compounding the problem, 92.7% of logged rows were sub-agent rows, and the share of main-thread versus sub-agent activity varied 48-fold across models — a result of deliberate orchestration policy, not random sampling. The author concludes that any cross-model comparison must stratify by role first, or risk measuring delegation patterns rather than model capability.
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