GPT-5.5 Leads Terminal-Bench 2.1 at 78.2% — The One Benchmark Opus 4.8 Still Trails
Claude Opus 4.8 leads on 12 of 13 major agentic benchmarks. Terminal-Bench 2.1 is the exception. GPT-5.5 scores 78.2% on the CLI automation benchmark, 3.6 points ahead of Opus 4.8’s 74.6%. Anthropic’s own system card includes the comparison without burying it.
The previous leader on Terminal-Bench 2.1 was Gemini 3.5 Flash at 76.2%, the same model that held top spot earlier this year on price-performance grounds. Both GPT-5.5 and Opus 4.8 have since cleared that number — GPT-5.5 by a wider margin.
Current Leaderboard
| Model | Terminal-Bench 2.1 |
|---|---|
| GPT-5.5 | 78.2% |
| Gemini 3.5 Flash | 76.2% (prior leader) |
| Claude Opus 4.8 | 74.6% |
| Claude Opus 4.7 | 66.1% |
| DeepSeek V4 Pro | 67.9% |
| MiniMax M3 | 66.0% |
| Gemini 3.1 Pro | 68.1% |
Terminal-Bench 2.1 measures autonomous multi-step shell execution: a model gets a terminal, a task, and no hand-holding. It has to issue commands, read error output, recover from failures, and complete the task without human intervention. Scores represent the percentage of tasks completed end-to-end.
What the Gap Means
GPT-5.5’s 78.2% advantage is consistent across runs per multiple independent analyses. The model handles specific error patterns — particularly correction loops on shell execution failures — more robustly than Opus 4.8. Opus 4.8 gets stuck in those loops at a measurably higher rate.
Against every other major agentic benchmark, Opus 4.8 is ahead:
- SWE-bench Pro: 69.2% (Opus 4.8) vs 58.6% (GPT-5.5)
- OSWorld-Verified computer use: 83.4% vs ~79%
- GDPval-AA knowledge work: 1890 Elo vs 1769
- Humanity’s Last Exam with tools: 57.9% vs ~52%
The pattern is clear: Opus 4.8 is the stronger general-purpose and coding agent. GPT-5.5 is the stronger terminal-native agent. Neither gap is large enough that scaffolding can’t close it — Terminal-Bench results are harness-sensitive, and the vix scaffold that currently holds the overall Terminal-Bench 2.0 lead runs Claude Opus 4.7.
Selection Guidance
Teams building overnight CLI agents that run autonomously on infrastructure tasks have a genuine reason to favor GPT-5.5. Teams building coding agents, multi-turn research tasks, or computer-use pipelines should favor Opus 4.8 by a larger margin.
The frontier at mid-2026 has fractured by workload type. Single-model stacks optimized around one benchmark are increasingly wrong.