GPT-5.1 Codex vs Kimi K3 for coding
GPT-5.1 Codex is the stronger coder of the two on benchmarks, but Kimi K3 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 | Kimi K3 |
|---|---|---|
| Provider | OpenAI | Moonshot AI |
| Released | Nov 2025 | Dec 2025 |
| SWE-bench Verified | 75% | 70% |
| HumanEval | 95% | 93% |
| MMLU | 88% | 87% |
| Context window | 400K | 2M |
| Max output | 128K | 16K |
| Input price (per 1M) | $1.25 | $0.60 |
| Output price (per 1M) | $10 | $2.50 |
| Price tier | Mid | Budget |
| Speed | Medium | Medium |
| Hosting | Closed/API | Closed/API + Self-host |
| Modality | Text + Vision | Multimodal (vision) |
| Knowledge cutoff | Oct 2025 | Oct 2025 |
Pick GPT-5.1 Codex if…
- It scores higher on SWE-bench Verified (75% vs 70%), the best proxy for real-world coding.
- It's tuned for codex CLI and long-horizon coding agents; engineered for terminal-driven workflows.
Pick Kimi K3 if…
- It's cheaper (Budget tier vs Mid).
- It has a larger context window (2M vs 400K).
- It's tuned for agentic coding at low cost, ultra-long context, China-region deployments.
GPT-5.1 Codex vs Kimi K3: which is better for coding?
GPT-5.1 Codex is the stronger coder of the two on benchmarks, but Kimi K3 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.