Same model, 5x cost gap: harness choice matters more than success rate

JeremyCMorgan · x · 2026-09-25

Berkeley and Arena ran 7 models through Claude Code, Codex CLI and Pi. Success rates moved only a couple of points, but cost moved up to 5x on the same tasks. If you pay per token, the harness is a line item — check sample-size limits before switching.

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