# GPT-5.1-Codex vs GPT-5.5 Pro

> GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 38.2 on the Noometry Index. GPT-5.1-Codex costs 20× less per token, which makes it the better buy when GPT-5.5 Pro's lead doesn't matter for your workload.

- Canonical page: https://noometry.com/compare/gpt-5-1-codex-vs-gpt-5-5-pro
- Last updated: 2026-10-10
- Shared benchmarks: 0

## Summary

- The widest gap is in math, where GPT-5.5 Pro leads 83.8 to 29.3.
- GPT-5.1-Codex is cheaper at $1.25 / $10 per million input/output tokens, against $30 / $180 for GPT-5.5 Pro.
- GPT-5.5 Pro accepts more context: 1.05M tokens versus 400K.

## Snapshot

| | GPT-5.1-Codex | GPT-5.5 Pro |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 38.2 | 64.3 |
| Rank | 178 | 7 |
| Context | 400K | 1.05M |
| Input $/M | $1.25 | $30 |
| Output $/M | $10 | $180 |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5.1-Codex: 41.7 (#107)
- GPT-5.5 Pro: —

| Benchmark | GPT-5.1-Codex | GPT-5.5 Pro |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1337 | — |
| ALE-Bench | 1,245 | — |

## Agentic & Tool Use

- GPT-5.1-Codex: 37.8 (#32)
- GPT-5.5 Pro: —

| Benchmark | GPT-5.1-Codex | GPT-5.5 Pro |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| METR Time Horizons | 70.8% | — |

## Reasoning

- GPT-5.1-Codex: —
- GPT-5.5 Pro: 73.6 (#7)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Pro |
|---|---|---|
| ARC-AGI-2 | — | 84.6% |
| SimpleBench | — | 76.9% |
| ARC-AGI-1 | — | 96.5% |
| CritPt | — | 30.6% |
| Chess Puzzles | — | 64% |
| DTBench | — | 96% |
| LMCA | — | 53.9% |
| Epoch Capabilities Index | — | 162.45 |

## Math

- GPT-5.1-Codex: 29.3 (#218)
- GPT-5.5 Pro: 83.8 (#8)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Pro |
|---|---|---|
| FrontierMath (Tiers 1-3) | — | 87.7% |
| FrontierMath Tier 4 | — | 78% |
| OTIS Mock AIME 2024-2025 | — | 100% |
| ProofBench | 9% | — |
| FrontierMath (Feb 2025 set) | — | 52.4% |
| FrontierMath Tier 4 (v1) | — | 39.6% |

## Knowledge

- GPT-5.1-Codex: —
- GPT-5.5 Pro: 64.2 (#17)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Pro |
|---|---|---|
| GPQA Diamond | — | 93.9% |

## FAQ

### Is GPT-5.1-Codex better than GPT-5.5 Pro?

GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 38.2 on the Noometry Index. GPT-5.1-Codex costs 20× less per token, which makes it the better buy when GPT-5.5 Pro's lead doesn't matter for your workload.

### Which is cheaper, GPT-5.1-Codex or GPT-5.5 Pro?

GPT-5.1-Codex is cheaper. It lists at $1.25 per million input tokens and $10 per million output tokens; GPT-5.5 Pro lists at $30 and $180.

### Which has the bigger context window?

GPT-5.5 Pro does, with 1.05M tokens against 400K.

### How many benchmarks do GPT-5.1-Codex and GPT-5.5 Pro share?

0 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and GPT-5.5 Pro has 14.