# GPT-5.1-Codex vs GPT-5.5 Instant

> GPT-5.5 Instant is the stronger model overall, scoring 42.5 to 38.2 on the Noometry Index.

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

## Summary

- The widest gap is in math, where GPT-5.1-Codex leads 29.3 to 26.1.

## Snapshot

| | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 38.2 | 42.5 |
| Rank | 178 | 99 |
| Context | 400K | — |
| Input $/M | $1.25 | — |
| Output $/M | $10 | — |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5.1-Codex: 41.7 (#107)
- GPT-5.5 Instant: 43.7 (#73)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1337 | — |
| SciCode | — | 48.6% |
| LMArena Coding | — | 1433 |
| ALE-Bench | 1,245 | — |

## Agentic & Tool Use

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

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

## Reasoning

- GPT-5.1-Codex: —
- GPT-5.5 Instant: 24.2 (#149)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| CritPt | — | 0% |
| Chess Puzzles | — | 12% |
| LMArena Hard Prompts | — | 1426 |
| Epoch Capabilities Index | — | 142.48 |

## Math

- GPT-5.1-Codex: 29.3 (#218)
- GPT-5.5 Instant: 26.1 (#241)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| FrontierMath (Tiers 1-3) | — | 26.3% |
| FrontierMath Tier 4 | — | 2.4% |
| OTIS Mock AIME 2024-2025 | — | 68.1% |
| ProofBench | 9% | — |
| LMArena Math | — | 1420 |

## Knowledge

- GPT-5.1-Codex: —
- GPT-5.5 Instant: 48.9 (#68)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| GPQA Diamond | — | 82.5% |
| LMArena Expert | — | 1409 |

## Multimodal

- GPT-5.1-Codex: —
- GPT-5.5 Instant: 39.3 (#48)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Vision | — | 1250 |
| LMArena Document | — | 1403 |

## Multilingual

- GPT-5.1-Codex: —
- GPT-5.5 Instant: 53.0 (#76)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Non-English | — | 1417 |
| LMArena Chinese | — | 1457 |
| LMArena French | — | 1428 |
| LMArena German | — | 1410 |
| LMArena Japanese | — | 1408 |
| LMArena Korean | — | 1393 |
| LMArena Russian | — | 1430 |
| LMArena Spanish | — | 1430 |

## Instruction Following

- GPT-5.1-Codex: —
- GPT-5.5 Instant: 74.4 (#94)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Instruction Following | — | 1407 |

## Long Context

- GPT-5.1-Codex: —
- GPT-5.5 Instant: 43.4 (#92)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Longer Query | — | 1422 |

## Writing & Preference

- GPT-5.1-Codex: —
- GPT-5.5 Instant: 62.0 (#81)

| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Text | — | 1419 |
| LMArena Creative Writing | — | 1420 |
| LMArena Multi-Turn | — | 1434 |

## FAQ

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

GPT-5.5 Instant is the stronger model overall, scoring 42.5 to 38.2 on the Noometry Index.

### Is GPT-5.1-Codex or GPT-5.5 Instant better for coding?

GPT-5.5 Instant scores higher on coding benchmarks: 43.7 versus 41.7 in the Noometry coding category.

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

0 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and GPT-5.5 Instant has 27.