# Gemini 3 Flash vs GPT-5.1-Codex

> Side-by-side benchmark comparison for Gemini 3 Flash and GPT-5.1-Codex across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/gemini-3-flash-vs-gpt-5-1-codex
- Last updated: September 29, 2026

- Shared sourced benchmarks: 4
- HTML indexing: indexable
- Ranking lane: BenchAlign v5.7

## Quick Verdict

Pick Gemini 3 Flash if you want the stronger benchmark profile. GPT-5.1-Codex only makes more sense when its price, context window, or workload-specific category wins matter more than the overall score.

## Summary

- Gemini 3 Flash leads overall 55.5 to 44.38.
- The clearest category separation is in instruction following, where the averages are 64.7 for Gemini 3 Flash and 84.2 for GPT-5.1-Codex.
- The biggest single benchmark swing is JobBench in Agentic, with scores of 11.4% and 26.2%.
- Gemini 3 Flash is the cheaper option on output tokens, which matters if you expect large responses or heavy interactive use.
- Gemini 3 Flash also has the larger context window at 1M.

## Model Snapshot

| Property | Gemini 3 Flash | GPT-5.1-Codex |
|----------|----------|----------|
| Creator | Google | OpenAI |
| Type | Proprietary | Proprietary |
| Reasoning | Non-Reasoning | Reasoning |
| Context | 1M | 400K |
| Overall Score | 55.5 | 44.38 |
| Benchmarks Covered | 11 | 4 |
| Pricing (input/output) | $0.50 / $3.00 | $1.25 / $10.00 |

## Category Breakdown

### Agentic

- Winner: Not comparable
- Gemini 3 Flash public-lane score: 31.7 (Supported · #76/117)
- GPT-5.1-Codex public-lane score: Coming soon

| Benchmark | Gemini 3 Flash | GPT-5.1-Codex | Winner |
|-----------|-----------|-----------|--------|
| Claw-Eval | 49.2% | Coming soon | Coming soon |
| Gert Labs | 56.63% | 49.68% | Gemini 3 Flash |
| JobBench | 11.4% | 26.2% | GPT-5.1-Codex |
| Terminal-Bench 2.1 (Vals) | 53.9% | Coming soon | Coming soon |

### Coding

- Winner: Directional only
- Gemini 3 Flash public-lane score: 36.4 (Supported · #74/143)
- GPT-5.1-Codex public-lane score: 32.7 (Estimated · #85/143)

| Benchmark | Gemini 3 Flash | GPT-5.1-Codex | Winner |
|-----------|-----------|-----------|--------|
| Vibe Code Bench | 20.20% | 13.12% | Gemini 3 Flash |
| LiveCodeBench (Vals) | 85.6% | 85.6% | Tie |
| SWE-bench (Vals) | 75.0% | Coming soon | Coming soon |

### Reasoning

- Winner: Not comparable
- Gemini 3 Flash public-lane score: 60.3 (Unranked · 2 rankable rows)
- GPT-5.1-Codex public-lane score: 69.9 (Unranked · 2 rankable rows)

### Multimodal & Grounded

- Winner: Not comparable
- Gemini 3 Flash public-lane score: 76.9 (Unranked · 1 rankable row)
- GPT-5.1-Codex public-lane score: 67.9 (Unranked · 1 rankable row)

### Knowledge

- Winner: Directional only
- Gemini 3 Flash public-lane score: 54.3 (Supported · #47/169)
- GPT-5.1-Codex public-lane score: 48.1 (Estimated · #69/169)

| Benchmark | Gemini 3 Flash | GPT-5.1-Codex | Winner |
|-----------|-----------|-----------|--------|
| GPQA Diamond (Vals) | 87.9% | Coming soon | Coming soon |
| MMLU-Pro (Vals) | 88.6% | Coming soon | Coming soon |

### Instruction Following

- Winner: Directional only
- Gemini 3 Flash public-lane score: 64.7 (#70/124)
- GPT-5.1-Codex public-lane score: 84.2 (#42/124)

### Mathematics

- Winner: Not comparable
- Gemini 3 Flash public-lane score: 50 (Unranked · 2 rankable rows)
- GPT-5.1-Codex public-lane score: Coming soon

| Benchmark | Gemini 3 Flash | GPT-5.1-Codex | Winner |
|-----------|-----------|-----------|--------|
| FrontierMath v2 (Tiers 1-3) | 35.640% | Coming soon | Coming soon |
| FrontierMath v2 (Tier 4) | 4.167% | Coming soon | Coming soon |

## FAQ

### Which is better overall, Gemini 3 Flash or GPT-5.1-Codex?

Gemini 3 Flash is ahead overall on BenchLM right now.

### Where is the biggest gap between Gemini 3 Flash and GPT-5.1-Codex?

The widest category gap is in instruction following, where the averages are 64.7 for Gemini 3 Flash and 84.2 for GPT-5.1-Codex.

### How many benchmarks does Gemini 3 Flash cover on BenchLM?

Gemini 3 Flash currently has 11 sourced benchmark scores on BenchLM.

### How many benchmarks does GPT-5.1-Codex cover on BenchLM?

GPT-5.1-Codex currently has 4 sourced benchmark scores on BenchLM.

## Related Comparisons

- [Gemini 3 Flash vs GPT-6 Astra](/compare/gemini-3-flash-vs-gpt-6-astra)
- [GPT-5.1-Codex vs GPT-6 Astra](/compare/gpt-5-1-codex-vs-gpt-6-astra)
- [Gemini 3 Flash vs Claude Opus 5.5](/compare/claude-opus-5-5-vs-gemini-3-flash)
- [GPT-5.1-Codex vs Claude Opus 5.5](/compare/claude-opus-5-5-vs-gpt-5-1-codex)

## Explore More

- [Gemini 3 Flash profile](/models/gemini-3-flash)
- [GPT-5.1-Codex profile](/models/gpt-5-1-codex)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)