# DeepSeek V4.1 Flash vs GPT-5.1-Codex

> DeepSeek V4.1 Flash is the stronger model overall, scoring 52.8 to 38.6 on the Noometry Index.

- Canonical page: https://noometry.com/compare/deepseek-v4-1-flash-vs-gpt-5-1-codex
- Last updated: 2026-10-10
- Shared benchmarks: 3

## Summary

- They share 3 benchmarks with published results for both. DeepSeek V4.1 Flash scores higher in 2 categories and GPT-5.1-Codex in 1 category; 3 gaps are clear of the uncertainty.
- The widest gap is in math, where DeepSeek V4.1 Flash leads 66.7 to 30.3.
- The biggest single-benchmark swing is ProofBench: 54% for DeepSeek V4.1 Flash and 9% for GPT-5.1-Codex.
- DeepSeek V4.1 Flash is cheaper at $0.15 / $0.60 per million input/output tokens, against $1.25 / $10 for GPT-5.1-Codex.
- DeepSeek V4.1 Flash accepts more context: 1M tokens versus 400K.
- DeepSeek V4.1 Flash has downloadable open weights; the other is API-only.

## Snapshot

| | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| Provider | DeepSeek | OpenAI |
| Noometry Index | 52.8 | 38.6 |
| Rank | 38 | 186 |
| Context | 1M | 400K |
| Input $/M | $0.15 | $1.25 |
| Output $/M | $0.60 | $10 |
| Weights | Open | Proprietary |

## Coding

- DeepSeek V4.1 Flash: 52.9 (#32)
- GPT-5.1-Codex: 41.9 (#116)

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena WebDev | 1619 | 1337 |
| ALE-Bench | 1,092 | 1,245 |
| SWE-bench Verified (bash only) | — | 66% |
| SciCode | 51.9% | — |
| LMArena Coding | 1506 | — |

## Agentic & Tool Use

- DeepSeek V4.1 Flash: 31.2 (#69)
- GPT-5.1-Codex: 38.0 (#33)

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| Terminal-Bench | — | 60.4% |
| APEX-Agents | 39.5% | — |
| GDP.pdf | 19.8% | — |
| METR Time Horizons | — | 70.8% |

## Reasoning

- DeepSeek V4.1 Flash: 50.2 (#36)
- GPT-5.1-Codex: —

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| NYT Connections (extended) | 89.6% | — |
| CritPt | 14.3% | — |
| LMArena Hard Prompts | 1483 | — |
| Mystery Game Puzzles | 43% | — |
| DTBench | 89.9% | — |
| LMCA | 47% | — |
| Surface Evolver Bench | 46.3% | — |
| Epoch Capabilities Index | 154.9 | — |

## Math

- DeepSeek V4.1 Flash: 66.7 (#25)
- GPT-5.1-Codex: 30.3 (#235)

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| ProofBench | 54% | 9% |
| FrontierMath (Tiers 1-3) | 67.4% | — |
| FrontierMath Tier 4 | 26.8% | — |
| OTIS Mock AIME 2024-2025 | 98.3% | — |
| LMArena Math | 1477 | — |

## Knowledge

- DeepSeek V4.1 Flash: 57.9 (#38)
- GPT-5.1-Codex: —

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| GPQA Diamond | 89.8% | — |
| LMArena Expert | 1506 | — |

## Multimodal

- DeepSeek V4.1 Flash: 39.1 (#61)
- GPT-5.1-Codex: —

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Vision | 1277 | — |
| Furniture Assembly | 34.2% | — |

## Multilingual

- DeepSeek V4.1 Flash: 55.0 (#35)
- GPT-5.1-Codex: —

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Non-English | 1448 | — |
| LMArena Chinese | 1497 | — |
| LMArena French | 1452 | — |
| LMArena German | 1484 | — |
| LMArena Japanese | 1412 | — |
| LMArena Korean | 1452 | — |
| LMArena Russian | 1471 | — |
| LMArena Spanish | 1459 | — |

## Instruction Following

- DeepSeek V4.1 Flash: 77.3 (#26)
- GPT-5.1-Codex: —

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Instruction Following | 1474 | — |

## Long Context

- DeepSeek V4.1 Flash: 45.2 (#47)
- GPT-5.1-Codex: —

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Longer Query | 1475 | — |

## Writing & Preference

- DeepSeek V4.1 Flash: 65.4 (#48)
- GPT-5.1-Codex: —

| Benchmark | DeepSeek V4.1 Flash | GPT-5.1-Codex |
|---|---|---|
| LMArena Text | 1462 | — |
| LMArena Creative Writing | 1435 | — |
| EQ-Bench Creative Writing | 1540 | — |
| LMArena Multi-Turn | 1457 | — |

## FAQ

### Is DeepSeek V4.1 Flash better than GPT-5.1-Codex?

DeepSeek V4.1 Flash is the stronger model overall, scoring 52.8 to 38.6 on the Noometry Index.

### Which is cheaper, DeepSeek V4.1 Flash or GPT-5.1-Codex?

DeepSeek V4.1 Flash is cheaper. It lists at $0.15 per million input tokens and $0.60 per million output tokens; GPT-5.1-Codex lists at $1.25 and $10.

### Is DeepSeek V4.1 Flash or GPT-5.1-Codex better for coding?

DeepSeek V4.1 Flash scores higher on coding benchmarks: 52.9 versus 41.9 in the Noometry coding category.

### Which has the bigger context window?

DeepSeek V4.1 Flash does, with 1M tokens against 400K.

### How many benchmarks do DeepSeek V4.1 Flash and GPT-5.1-Codex share?

3 benchmarks have published results for both models. DeepSeek V4.1 Flash has 37 scored results on Noometry and GPT-5.1-Codex has 6.