# GPT-5.1-Codex vs GPT-5.3 Chat

> GPT-5.3 Chat is the stronger model overall, scoring 42.1 to 38.2 on the Noometry Index.

- Canonical page: https://noometry.com/compare/gpt-5-1-codex-vs-gpt-5-3-chat
- Last updated: 2026-10-10
- Shared benchmarks: 0

## Summary

- The widest gap is in math, where GPT-5.3 Chat leads 35.4 to 29.3.
- GPT-5.1-Codex is cheaper at $1.25 / $10 per million input/output tokens, against $1.75 / $14 for GPT-5.3 Chat.
- GPT-5.1-Codex accepts more context: 400K tokens versus 128K.

## Snapshot

| | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 38.2 | 42.1 |
| Rank | 178 | 109 |
| Context | 400K | 128K |
| Input $/M | $1.25 | $1.75 |
| Output $/M | $10 | $14 |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5.1-Codex: 41.7 (#107)
- GPT-5.3 Chat: 40.8 (#124)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1337 | — |
| LMArena Coding | — | 1408 |
| ALE-Bench | 1,245 | — |

## Agentic & Tool Use

- GPT-5.1-Codex: 37.8 (#32)
- GPT-5.3 Chat: —

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| METR Time Horizons | 70.8% | — |

## Reasoning

- GPT-5.1-Codex: —
- GPT-5.3 Chat: 27.3 (#105)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| LMArena Hard Prompts | — | 1399 |

## Math

- GPT-5.1-Codex: 29.3 (#218)
- GPT-5.3 Chat: 35.4 (#146)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| ProofBench | 9% | — |
| LMArena Math | — | 1389 |

## Knowledge

- GPT-5.1-Codex: —
- GPT-5.3 Chat: 38.2 (#137)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| LMArena Expert | — | 1397 |

## Multilingual

- GPT-5.1-Codex: —
- GPT-5.3 Chat: 50.5 (#119)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| LMArena Non-English | — | 1383 |
| LMArena Chinese | — | 1433 |
| LMArena French | — | 1398 |
| LMArena German | — | 1384 |
| LMArena Japanese | — | 1351 |
| LMArena Korean | — | 1347 |
| LMArena Russian | — | 1400 |
| LMArena Spanish | — | 1371 |

## Instruction Following

- GPT-5.1-Codex: —
- GPT-5.3 Chat: 73.0 (#124)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| LMArena Instruction Following | — | 1378 |

## Long Context

- GPT-5.1-Codex: —
- GPT-5.3 Chat: 42.6 (#115)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| LMArena Longer Query | — | 1396 |

## Writing & Preference

- GPT-5.1-Codex: —
- GPT-5.3 Chat: 63.3 (#65)

| Benchmark | GPT-5.1-Codex | GPT-5.3 Chat |
|---|---|---|
| LMArena Text | — | 1389 |
| LMArena Creative Writing | — | 1356 |
| EQ-Bench Creative Writing | — | 1690 |
| LMArena Multi-Turn | — | 1413 |

## FAQ

### Is GPT-5.1-Codex better than GPT-5.3 Chat?

GPT-5.3 Chat is the stronger model overall, scoring 42.1 to 38.2 on the Noometry Index.

### Which is cheaper, GPT-5.1-Codex or GPT-5.3 Chat?

GPT-5.1-Codex is cheaper. It lists at $1.25 per million input tokens and $10 per million output tokens; GPT-5.3 Chat lists at $1.75 and $14.

### Is GPT-5.1-Codex or GPT-5.3 Chat better for coding?

They score almost the same on coding (41.7 vs 40.8); test both on your own repository before choosing.

### Which has the bigger context window?

GPT-5.1-Codex does, with 400K tokens against 128K.

### How many benchmarks do GPT-5.1-Codex and GPT-5.3 Chat share?

0 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and GPT-5.3 Chat has 18.