Scaffolding

Plain English. The engineering built around a model to compensate for its weaknesses: retry logic, checkers, prompt chains, hand-tuned workflows. Related to but narrower than the harness — the harness is the durable machinery an agent runs in; scaffolding is the compensatory part, built because the model can't yet do something alone.

Why it moves money. "The model eats the scaffolding": each model release absorbs some of what applications laboriously built around the last one, so scaffolding-heavy products carry a depreciation schedule set by lab release cadence — the standing warning to application-layer investors. The clearest measurement: a third-party scaffold once beat Anthropic's own harness by 21.8 points on the identical model; within eight weeks of the next benchmark revision, the labs had pulled the advantage back in-house.

What to watch. The gap between the best third-party scaffold and lab-native harnesses on neutral benchmarks. Wide and stable favours the application layer; repeatedly closing favours the labs.

From the signals. Terminal-Bench flipped twice in eight weeks: the harness beat the model, then the labs took it back. The harness, not the model, is becoming the product surface. Lilian Weng's essay connects harness engineering to recursive self-improvement — applied to the scaffold, not the weights.