Making Optimization Work When Labels Are Scarce [R]

https://www.gnosyslabs.com/case-studies/safety-classifier-sparse-labels Gnosys is an autonomous model engineer: it improves prompts and classifiers when ground truth is too sparse for conventional optimization. On ToxicChat, a public safety benchmark, under realistic label scarcity, it improved a classifier past both the team's starting point and GEPA (a standard prompt optimizer), across two runs of our current method. This note describes what we did, what we found, and where the method underperformed. Results We report harm caught : the share of harmful messages flagged, holding the false positive rate fixed at 5% (one in twenty) for every method, so a difference reflects additional harm caught at the same cost rather than a change of threshold. Both runs below are scored on a held-out set the system never saw. Headline run (3,000) Prior run (1,000) Gnosys 0.777 0.909 Starting classifier 0.731 0.788 GEPA 0.702 0.848 In both runs, Gnosys improved on both the starting classifier and GEPA. In the headline run GEPA not only trailed Gnosys but fell below the starting classifier (0.731 to 0.702); in the prior run it improved on the starting point. This inconsistency is the central difficulty under sparse labels: optimization sometimes helps and sometimes harms, and without trustworthy measurement there is no way to tell which has happened. The comparison is intentionally conservative: both approaches use the same underlying optimizer. The only difference is that Gnosys engineers the objective the optimizer works against. The problem Teams running high-stakes AI classifiers, in content moderation, fraud, claims review, and risk scoring, share one constraint: the ground truth they need is a human judgment that is expensive, slow, and sometimes never arrives. They can verify only a small set of examples while decisions accumulate on everything else. Tuning the model against the few labels on hand is where the difficulty concentrates. Here "few" is literal: about 200 verifi