GPT-5.1 Codex vs Claude Haiku 4.5 (Fast) for coding
GPT-5.1 Codex is the stronger coder of the two on benchmarks, but Claude Haiku 4.5 (Fast) 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 | Claude Haiku 4.5 (Fast) |
|---|---|---|
| Provider | OpenAI | Anthropic |
| Released | Nov 2025 | Oct 2025 |
| SWE-bench Verified | 75% | 55% |
| HumanEval | 95% | 88% |
| MMLU | 88% | 82% |
| Context window | 400K | 200K |
| Max output | 128K | 32K |
| Input price (per 1M) | $1.25 | $1 |
| Output price (per 1M) | $10 | $5 |
| Price tier | Mid | Budget |
| Speed | Medium | Fast |
| Hosting | Closed/API | Closed/API |
| 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 55%), the best proxy for real-world coding.
- It has a larger context window (400K vs 200K).
- It's tuned for codex CLI and long-horizon coding agents; engineered for terminal-driven workflows.
Pick Claude Haiku 4.5 (Fast) if…
- It's cheaper (Budget tier vs Mid).
- It responds faster (Fast).
- It's tuned for high-throughput coding sidekick, autocomplete, batch jobs, and low-latency Claude Code use.
GPT-5.1 Codex vs Claude Haiku 4.5 (Fast): which is better for coding?
GPT-5.1 Codex is the stronger coder of the two on benchmarks, but Claude Haiku 4.5 (Fast) 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.