Do AI harnesses matter? Yes, KISS Sorcar outperforms three coding harnesses on Terminal-Bench 2.0. On Terminal-Bench 2.0, KISS Sorcar (
github.com/ksenxx/kiss_ai) solved 75.6% of attempts across seven models, the best rate on every model against Pi (70.0%), Codex CLI (65.7%), and Claude Code (65.1%), and in a paired rerun against Pi on Claude Fable 5, it won 80.0% to 68.9% at about the same cost per attempt. The three harness numbers come from the study below by
@melissapan et al. We ran KISS Sorcar on the same 30 tasks and seven models, three attempts per task.
We reran the Pi experiments: same tasks and prices, no turn cap for either agent, Pi at high effort with no budget cap. Pi cost $1.45 per attempt and KISS Sorcar $1.50; the gap was 11 points, paired with p = 0.016. On the 59 tasks the study didn't sample, KISS Sorcar solved 79.1%, and a second Pi rerun on 57 of them (two sat out because a dead package mirror broke the verifier) came out to 82.5% vs. 71.9%, a 10.5-point gap with p = 0.008, at 63 cents more per attempt. Two reruns on one model don't settle it, but on this benchmark the harness seems to matter more than the study's three harnesses showed. Full table and intervals:
kisssorcar.github.io/blog/ha…
Does your Claude model really need Claude Code…? 🤔
We evaluate 7 models on Claude Code, Codex, and Pi. Three surprising findings emerge:
1️⃣Harness choice has little effect on task success rate, but can significantly affect the cost
2️⃣A simple harness can be competitive
3️⃣The native harness isn’t always the best.
Millions of people are using coding agents, but the impact of harness choice remains unclear.
(1/n) More details in the thread. 🧵