# GPT-5.3 Codex vs GPT-5.5 Instant

> GPT-5.3 Codex is the stronger model overall, scoring 45.8 to 42.7 on the Noometry Index.

- Canonical page: https://noometry.com/compare/gpt-5-3-codex-vs-gpt-5-5-instant
- Last updated: 2026-10-12
- Shared benchmarks: 1

## Summary

- They share 1 benchmark with published results for both. GPT-5.3 Codex scores higher in 1 category and GPT-5.5 Instant in 0 categories; one gap is clear of the uncertainty.
- The widest gap is in coding, where GPT-5.3 Codex leads 48.6 to 44.3.

## Snapshot

| | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 45.8 | 42.7 |
| Rank | 69 | 110 |
| Context | 400K | — |
| Input $/M | $1.75 | — |
| Output $/M | $14 | — |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5.3 Codex: 48.6 (#56)
- GPT-5.5 Instant: 44.3 (#74)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| SWE-bench Verified | 74.8% | — |
| LMArena WebDev | 1409 | — |
| SciCode | — | 48.6% |
| WeirdML | 79.3% | — |
| LMArena Coding | — | 1433 |
| ALE-Bench | 1,655 | — |

## Agentic & Tool Use

- GPT-5.3 Codex: 48.0 (#9)
- GPT-5.5 Instant: —

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| Terminal-Bench | 78.4% | — |
| METR Time Horizons | 74.5% | — |
| Vending-Bench 2 | 5,940 | — |

## Reasoning

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 24.9 (#155)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| Epoch Capabilities Index | 156.77 | 142.52 |
| CritPt | — | 0% |
| Chess Puzzles | — | 12% |
| LMArena Hard Prompts | — | 1426 |

## Math

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 26.5 (#259)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| FrontierMath (Tiers 1-3) | — | 26.3% |
| FrontierMath Tier 4 | — | 2.4% |
| OTIS Mock AIME 2024-2025 | — | 68.1% |
| LMArena Math | — | 1420 |

## Knowledge

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 48.9 (#74)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| GPQA Diamond | — | 82.5% |
| LMArena Expert | — | 1409 |

## Multimodal

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 40.0 (#52)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Vision | — | 1250 |
| LMArena Document | — | 1403 |

## Multilingual

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 52.8 (#80)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Non-English | — | 1417 |
| LMArena Chinese | — | 1456 |
| LMArena French | — | 1428 |
| LMArena German | — | 1411 |
| LMArena Japanese | — | 1408 |
| LMArena Korean | — | 1392 |
| LMArena Russian | — | 1431 |
| LMArena Spanish | — | 1429 |

## Instruction Following

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 74.2 (#100)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Instruction Following | — | 1406 |

## Long Context

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 43.4 (#96)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Longer Query | — | 1422 |

## Writing & Preference

- GPT-5.3 Codex: —
- GPT-5.5 Instant: 61.8 (#85)

| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Text | — | 1419 |
| LMArena Creative Writing | — | 1419 |
| LMArena Multi-Turn | — | 1433 |

## FAQ

### Is GPT-5.3 Codex better than GPT-5.5 Instant?

GPT-5.3 Codex is the stronger model overall, scoring 45.8 to 42.7 on the Noometry Index.

### Is GPT-5.3 Codex or GPT-5.5 Instant better for coding?

GPT-5.3 Codex scores higher on coding benchmarks: 48.6 versus 44.3 in the Noometry coding category.

### How many benchmarks do GPT-5.3 Codex and GPT-5.5 Instant share?

1 benchmark has published results for both models. GPT-5.3 Codex has 8 scored results on Noometry and GPT-5.5 Instant has 27.