NVIDIA's ACES framework defines Skill Lift as with-skill minus without-skill on paired live agent trajectories, grading discovery, workflow, tool efficiency, and accuracy — not static document scans. In August 2026 production-skill evals across 947 cases, mean composite Skill Lift was +0.21, but roughly 27% of pairs showed zero or negative lift, meaning scan-only quality scores did not predict runtime value.