# Gemini 2.5 Flash vs GPT-5.1-Codex

> Gemini 2.5 Flash and GPT-5.1-Codex score almost the same on the Noometry Index (39.0 vs 38.2), so choose on price, context window or the category you care about most.

- Canonical page: https://noometry.com/compare/gemini-2-5-flash-vs-gpt-5-1-codex
- Last updated: 2026-10-10
- Shared benchmarks: 3

## Summary

- They share 3 benchmarks with published results for both. Gemini 2.5 Flash scores higher in 1 category and GPT-5.1-Codex in 2 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in math, where Gemini 2.5 Flash leads 38.1 to 29.3.
- The biggest single-benchmark swing is Terminal-Bench: 17.1% for Gemini 2.5 Flash and 60.4% for GPT-5.1-Codex.
- Gemini 2.5 Flash is cheaper at $0.30 / $2.50 per million input/output tokens, against $1.25 / $10 for GPT-5.1-Codex.
- Gemini 2.5 Flash accepts more context: 1.05M tokens versus 400K.

## Snapshot

| | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| Provider | Google | OpenAI |
| Noometry Index | 39.0 | 38.2 |
| Rank | 162 | 178 |
| Context | 1.05M | 400K |
| Input $/M | $0.30 | $1.25 |
| Output $/M | $2.50 | $10 |
| Weights | Proprietary | Proprietary |

## Coding

- Gemini 2.5 Flash: 35.5 (#210)
- GPT-5.1-Codex: 41.7 (#107)

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| SWE-bench Verified (bash only) | 28.7% | 66% |
| ALE-Bench | 661.88 | 1,245 |
| Aider Polyglot | 55.1% | — |
| LMArena WebDev | — | 1337 |
| WeirdML | 41.9% | — |
| LMArena Coding | 1424 | — |

## Agentic & Tool Use

- Gemini 2.5 Flash: 30.6 (#67)
- GPT-5.1-Codex: 37.8 (#32)

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| Terminal-Bench | 17.1% | 60.4% |
| Berkeley Function Calling Leaderboard | 56.2% | — |
| TheAgentCompany | 41.1% | — |
| BALROG | 33.5% | — |
| METR Time Horizons | — | 70.8% |
| Vending-Bench 2 | 548.84 | — |

## Reasoning

- Gemini 2.5 Flash: 18.2 (#271)
- GPT-5.1-Codex: —

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| ARC-AGI-2 | 2.5% | — |
| SimpleBench | 41.2% | — |
| Kagi LLM Benchmark | 56.8% | — |
| ARC-AGI-1 | 33.3% | — |
| CritPt | 1.1% | — |
| EnigmaEval | 2.7% | — |
| LMArena Hard Prompts | 1422 | — |
| DTBench | 76.5% | — |
| LMCA | 27.5% | — |
| Epoch Capabilities Index | 143.04 | — |
| ForecastBench | 60.6 | — |

## Math

- Gemini 2.5 Flash: 38.1 (#87)
- GPT-5.1-Codex: 29.3 (#218)

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| OTIS Mock AIME 2024-2025 | 73.1% | — |
| ProofBench | — | 9% |
| Omni-MATH | 38.5% | — |
| LMArena Math | 1415 | — |
| FrontierMath (Feb 2025 set) | 4.8% | — |
| FrontierMath Tier 4 (v1) | 4.2% | — |

## Knowledge

- Gemini 2.5 Flash: 36.1 (#162)
- GPT-5.1-Codex: —

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| Humanity's Last Exam | 12.1% | — |
| MMLU-Pro | 63.9% | — |
| Confabulations | 16.8% | — |
| Vectara Hallucination Rate | 7.8% | — |
| GPQA (HELM) | 39% | — |
| LMArena Expert | 1426 | — |

## Multimodal

- Gemini 2.5 Flash: 41.2 (#31)
- GPT-5.1-Codex: —

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Vision | 1254 | — |
| GeoBench | 76% | — |
| VPCT | 46.2% | — |
| SpatialViz-Bench | 36.9% | — |

## Multilingual

- Gemini 2.5 Flash: 52.5 (#83)
- GPT-5.1-Codex: —

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Non-English | 1410 | — |
| LMArena Chinese | 1450 | — |
| LMArena French | 1433 | — |
| LMArena German | 1419 | — |
| LMArena Japanese | 1403 | — |
| LMArena Korean | 1385 | — |
| LMArena Russian | 1415 | — |
| LMArena Spanish | 1421 | — |

## Instruction Following

- Gemini 2.5 Flash: 75.9 (#50)
- GPT-5.1-Codex: —

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| IFEval | 89.8% | — |
| LMArena Instruction Following | 1405 | — |

## Long Context

- Gemini 2.5 Flash: 47.5 (#16)
- GPT-5.1-Codex: —

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| Fiction.LiveBench | 77.8% | — |
| LMArena Longer Query | 1419 | — |

## Writing & Preference

- Gemini 2.5 Flash: 54.0 (#153)
- GPT-5.1-Codex: —

| Benchmark | Gemini 2.5 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Text | 1417 | — |
| LMArena Creative Writing | 1400 | — |
| Short-Story Creative Writing | 76.5% | — |
| EQ-Bench Creative Writing | 1137 | — |
| WildBench | 81.7% | — |
| LMArena Multi-Turn | 1408 | — |

## FAQ

### Is Gemini 2.5 Flash better than GPT-5.1-Codex?

Gemini 2.5 Flash and GPT-5.1-Codex score almost the same on the Noometry Index (39.0 vs 38.2), so choose on price, context window or the category you care about most.

### Which is cheaper, Gemini 2.5 Flash or GPT-5.1-Codex?

Gemini 2.5 Flash is cheaper. It lists at $0.30 per million input tokens and $2.50 per million output tokens; GPT-5.1-Codex lists at $1.25 and $10.

### Is Gemini 2.5 Flash or GPT-5.1-Codex better for coding?

GPT-5.1-Codex scores higher on coding benchmarks: 41.7 versus 35.5 in the Noometry coding category.

### Which has the bigger context window?

Gemini 2.5 Flash does, with 1.05M tokens against 400K.

### How many benchmarks do Gemini 2.5 Flash and GPT-5.1-Codex share?

3 benchmarks have published results for both models. Gemini 2.5 Flash has 54 scored results on Noometry and GPT-5.1-Codex has 6.