Claude Opus 5.5 scores 72.4 on the Respan Index (#1), ahead of Step 5 Preview at 54.9 (#12). Claude Opus 5.5 leads on 4 of the 4 benchmarks both report. Step 5 Preview is 5.6x cheaper per token at list price.
| Benchmark | Claude Opus 5.5 | Step 5 Preview |
|---|---|---|
| Terminal-Bench 4.0 (Vals AI) | 65.2% | 31.8% |
| LMArena Agent (LMArena) | 0.1382 | 0.0048 |
| LMArena Elo | 1504 | 1454 |
| LMArena WebDev (LMArena) | 1815 | 1570 |
Higher is better. Each score links to where it was published.
* Estimated: no published scores in that category. How the Respan Index works