# GPT-5.3 Codex vs Mistral Medium 3.5 128B

> Side-by-side benchmark comparison for GPT-5.3 Codex and Mistral Medium 3.5 128B across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/gpt-5-3-codex-vs-mistral-medium-3-5-128b
- Last updated: September 10, 2026

- Shared sourced benchmarks: 2
- HTML indexing: indexable
- Ranking lane: BenchAlign v5

## Quick Verdict

Evidence is too thin for a benchmark verdict: GPT-5.3 Codex and Mistral Medium 3.5 128B share only 2 sourced benchmark rows.

## Summary

- Only 2 shared sourced benchmark rows are available. That is not enough for a broad capability verdict, so this mirror does not name an overall winner.
- Mistral Medium 3.5 128B has the lower published output-token price.
- GPT-5.3 Codex has the larger published context window at 400K.

## Model Snapshot

| Property | GPT-5.3 Codex | Mistral Medium 3.5 128B |
|----------|----------|----------|
| Creator | OpenAI | Mistral |
| Type | Proprietary | Open Weight |
| Reasoning | Reasoning | Reasoning |
| Context | 400K | 256K |
| Independent public score (not head-to-head) | 64.29 | 30.13 |
| Benchmarks Covered | 8 | 7 |
| Pricing (input/output) | $1.75 / $14.00 | $1.50 / $7.50 |

## Category Breakdown

### Agentic

- Winner: Insufficient shared evidence
- GPT-5.3 Codex public-lane score: 61.6 (Estimated · #15/152)
- Mistral Medium 3.5 128B public-lane score: 21.9 (Supported · #150/152)

| Benchmark | GPT-5.3 Codex | Mistral Medium 3.5 128B | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.0 | 77.3% | Coming soon | Coming soon |
| OSWorld-Verified | 64.7% | Coming soon | Coming soon |
| Gert Labs | 57.47% | 39.10% | GPT-5.3 Codex |
| JobBench | 33.7% | Coming soon | Coming soon |
| τ³-bench results | Coming soon | 91.4% | Coming soon |
| Terminal-Bench 2.1 (Vals) | Coming soon | 39.0% | Coming soon |

### Coding

- Winner: Insufficient shared evidence
- GPT-5.3 Codex public-lane score: 62 (Estimated · #17/151)
- Mistral Medium 3.5 128B public-lane score: 36.9 (Estimated · #127/151)

| Benchmark | GPT-5.3 Codex | Mistral Medium 3.5 128B | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | 85% | 77.6% | GPT-5.3 Codex |
| SWE-bench Pro | 56.8% | Coming soon | Coming soon |
| SWE-Rebench | 58.2% | Coming soon | Coming soon |
| Vibe Code Bench | 61.77% | Coming soon | Coming soon |
| SWE-bench (Vals) | Coming soon | 66.4% | Coming soon |

### Multimodal & Grounded

- Winner: Insufficient shared evidence
- GPT-5.3 Codex public-lane score: 75.6 (Unranked · 1 rankable row)
- Mistral Medium 3.5 128B public-lane score: 55.6 (Unranked · 1 rankable row)

### Reasoning

- Winner: Insufficient shared evidence
- GPT-5.3 Codex public-lane score: 78.3 (Unranked · 2 rankable rows)
- Mistral Medium 3.5 128B public-lane score: 68.6 (Unranked · 2 rankable rows)

### Knowledge

- Winner: Insufficient shared evidence
- GPT-5.3 Codex public-lane score: 65.6 (Estimated · #23/183)
- Mistral Medium 3.5 128B public-lane score: 39 (Supported · #140/183)

| Benchmark | GPT-5.3 Codex | Mistral Medium 3.5 128B | Winner |
|-----------|-----------|-----------|--------|
| GPQA Diamond (Vals) | Coming soon | 34.8% | Coming soon |
| MMLU-Pro (Vals) | Coming soon | 75.3% | Coming soon |

### Instruction Following

- Winner: Insufficient shared evidence
- GPT-5.3 Codex public-lane score: 92.6 (#15/123)
- Mistral Medium 3.5 128B public-lane score: 84 (#48/123)

## FAQ

### Is there enough evidence to pick between GPT-5.3 Codex and Mistral Medium 3.5 128B?

Not yet. The models share only 2 sourced benchmark rows, so this mirror reports the available measurements and metadata without naming a broad winner.

### What can I compare safely on this page?

Published pricing, context windows, model type, and individual shared benchmark rows are directly comparable. Independent overall scores and non-overlapping benchmark coverage are labeled separately and should not be read as a controlled head-to-head result.

## Related Comparisons

- [GPT-5.3 Codex vs GPT-5.3-Codex-Spark](/compare/gpt-5-3-codex-vs-gpt-5-3-codex-spark)
- [Mistral Medium 3.5 128B vs GPT-5.3-Codex-Spark](/compare/gpt-5-3-codex-spark-vs-mistral-medium-3-5-128b)
- [GPT-5.3 Codex vs Claude Fable 5.1](/compare/claude-fable-5-1-vs-gpt-5-3-codex)
- [Mistral Medium 3.5 128B vs Claude Fable 5.1](/compare/claude-fable-5-1-vs-mistral-medium-3-5-128b)

## Explore More

- [GPT-5.3 Codex profile](/models/gpt-5-3-codex)
- [Mistral Medium 3.5 128B profile](/models/mistral-medium-3-5-128b)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)