GPT-5.1 Codex vs Grok Code Fast 2 for coding
GPT-5.1 Codex is the stronger coder of the two on benchmarks, but Grok Code Fast 2 can be the better pick when cost, speed, or context window matter more. Below: a side-by-side spec table and exactly when to pick each.
At a glance
| Spec | GPT-5.1 Codex | Grok Code Fast 2 |
|---|---|---|
| Provider | OpenAI | xAI |
| Released | Nov 2025 | Dec 2025 |
| SWE-bench Verified | 75% | 65% |
| HumanEval | 95% | 91% |
| MMLU | 88% | 85% |
| Context window | 400K | 256K |
| Max output | 128K | 32K |
| Input price (per 1M) | $1.25 | $0.20 |
| Output price (per 1M) | $10 | $1.50 |
| Price tier | Mid | Budget |
| Speed | Medium | Fast |
| Hosting | Closed/API | Closed/API |
| Modality | Text + Vision | Text |
| Knowledge cutoff | Oct 2025 | Nov 2025 |
Pick GPT-5.1 Codex if…
- It scores higher on SWE-bench Verified (75% vs 65%), the best proxy for real-world coding.
- It has a larger context window (400K vs 256K).
- It's tuned for codex CLI and long-horizon coding agents; engineered for terminal-driven workflows.
Pick Grok Code Fast 2 if…
- It's cheaper (Budget tier vs Mid).
- It responds faster (Fast).
- It's tuned for high-volume agentic coding where latency and cost trump max intelligence.
GPT-5.1 Codex vs Grok Code Fast 2: which is better for coding?
GPT-5.1 Codex is the stronger coder of the two on benchmarks, but Grok Code Fast 2 can be the better pick when cost, speed, or context window matter more. See the full spec table for SWE-bench, HumanEval, MMLU, context window, and pricing on both. Benchmarks are a directional signal, not a guarantee for your codebase — the most reliable test is running both on a real task you care about.
Compare these head-to-head with live data, or build a full stack around your pick — Flowpicker shows compatibility and monthly cost.
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See the full model leaderboard ranked by SWE-bench, HumanEval, and MMLU.