# GPT-5.3 Codex vs Kimi K2.5 (Reasoning)

> Side-by-side benchmark comparison for GPT-5.3 Codex and Kimi K2.5 (Reasoning) across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/gpt-5-3-codex-vs-kimi-k2-5-reasoning
- Last updated: October 17, 2026

- Shared sourced benchmarks: 6
- HTML indexing: indexable
- Ranking lane: BenchAlign v5.8

## Quick Verdict

GPT-5.3 Codex leads by point estimate. Conditional score ranges do not establish rank confidence. Choose using the category evidence and your own workload tests.

## Summary

- GPT-5.3 Codex has the higher overall point estimate 60.48 to 56.09. Conditional score ranges do not establish rank confidence.
- The clearest category separation is in agentic, where the averages are 55.5 for GPT-5.3 Codex and 38.3 for Kimi K2.5 (Reasoning).
- The biggest single benchmark swing is Vibe Code Bench in Coding, with scores of 61.77% and 17.54%.
- Kimi K2.5 (Reasoning) is the cheaper option on output tokens, which matters if you expect large responses or heavy interactive use.
- GPT-5.3 Codex also has the larger context window at 400K.

## Model Snapshot

| Property | GPT-5.3 Codex | Kimi K2.5 (Reasoning) |
|----------|----------|----------|
| Creator | OpenAI | Moonshot AI |
| Type | Proprietary | Proprietary |
| Reasoning | Reasoning | Reasoning |
| Context | 400K | 128K |
| Overall Score | 60.48 | 56.09 |
| Benchmarks Covered | 11 | 15 |
| Pricing (input/output) | $1.75 / $14.00 | $0.60 / $3.00 |

## Category Breakdown

### Agentic

- Winner: Directional only
- GPT-5.3 Codex public-lane score: 55.5 (Estimated · #41/128)
- Kimi K2.5 (Reasoning) public-lane score: 38.3 (Estimated · #71/128)

| Benchmark | GPT-5.3 Codex | Kimi K2.5 (Reasoning) | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.0 | 77.3% | 50.8% | GPT-5.3 Codex |
| OSWorld-Verified | 64.7% | 63.3% | GPT-5.3 Codex |
| Gert Labs | 57.47% | 32.58% | GPT-5.3 Codex |
| JobBench | 33.7% | Coming soon | Coming soon |
| BrowseComp | Coming soon | 60.6% | Coming soon |

### Coding

- Winner: Not comparable
- GPT-5.3 Codex public-lane score: 53.5 (Supported · #35/150)
- Kimi K2.5 (Reasoning) public-lane score: Coming soon

| Benchmark | GPT-5.3 Codex | Kimi K2.5 (Reasoning) | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | 85% | 76.8% | GPT-5.3 Codex |
| SWE-bench Pro | 56.8% | Coming soon | Coming soon |
| SWE-Rebench | 58.2% | Coming soon | Coming soon |
| Terminal-Bench 2.0 | 77.3% | 50.8% | GPT-5.3 Codex |
| Vibe Code Bench | 61.77% | 17.54% | GPT-5.3 Codex |
| LiveCodeBench (Vals) | 87.3% | Coming soon | Coming soon |
| SWE-bench (Vals) | 78.0% | Coming soon | Coming soon |
| LiveCodeBench v6 | Coming soon | 85.0% | Coming soon |

### Reasoning

- Winner: Not comparable
- GPT-5.3 Codex public-lane score: 83.1 (Unranked · 2 rankable rows)
- Kimi K2.5 (Reasoning) public-lane score: 67.1 (Unranked · 1 rankable row)

| Benchmark | GPT-5.3 Codex | Kimi K2.5 (Reasoning) | Winner |
|-----------|-----------|-----------|--------|
| LongBench v2 | Coming soon | 61% | Coming soon |

### Multimodal & Grounded

- Winner: Not comparable
- GPT-5.3 Codex public-lane score: 80.1 (Unranked · 1 rankable row)
- Kimi K2.5 (Reasoning) public-lane score: 69 (#33/54)

| Benchmark | GPT-5.3 Codex | Kimi K2.5 (Reasoning) | Winner |
|-----------|-----------|-----------|--------|
| MMMU-Pro | Coming soon | 78.5% | Coming soon |
| CharXiv | Coming soon | 77.5% | Coming soon |

### Knowledge

- Winner: Directional only
- GPT-5.3 Codex public-lane score: 65.4 (Estimated · #33/184)
- Kimi K2.5 (Reasoning) public-lane score: 48.8 (Estimated · #85/184)

| Benchmark | GPT-5.3 Codex | Kimi K2.5 (Reasoning) | Winner |
|-----------|-----------|-----------|--------|
| GPQA | Coming soon | 87.6% | Coming soon |
| MMLU-Pro | Coming soon | 87.1% | Coming soon |

### Instruction Following

- Winner: Not comparable
- GPT-5.3 Codex public-lane score: 92.6 (#18/148)
- Kimi K2.5 (Reasoning) public-lane score: Coming soon

### Mathematics

- Winner: Not comparable
- GPT-5.3 Codex public-lane score: Coming soon
- Kimi K2.5 (Reasoning) public-lane score: Coming soon

| Benchmark | GPT-5.3 Codex | Kimi K2.5 (Reasoning) | Winner |
|-----------|-----------|-----------|--------|
| AIME 2025 | Coming soon | 96.1% | Coming soon |
| HMMT Feb 2025 | Coming soon | 95.4% | Coming soon |

## FAQ

### Which is better overall, GPT-5.3 Codex or Kimi K2.5 (Reasoning)?

GPT-5.3 Codex has the higher overall point estimate. Conditional score ranges do not establish rank confidence.

### Where is the biggest gap between GPT-5.3 Codex and Kimi K2.5 (Reasoning)?

The widest category gap is in agentic, where the averages are 55.5 for GPT-5.3 Codex and 38.3 for Kimi K2.5 (Reasoning).

### How many benchmarks does GPT-5.3 Codex cover on BenchLM?

GPT-5.3 Codex currently has 11 sourced benchmark scores on BenchLM.

### How many benchmarks does Kimi K2.5 (Reasoning) cover on BenchLM?

Kimi K2.5 (Reasoning) currently has 15 sourced benchmark scores on BenchLM.

## Related Comparisons

- [GPT-5.3 Codex vs GPT-5.3-Codex-Spark](/compare/gpt-5-3-codex-vs-gpt-5-3-codex-spark)
- [Kimi K2.5 (Reasoning) vs GPT-5.3-Codex-Spark](/compare/gpt-5-3-codex-spark-vs-kimi-k2-5-reasoning)
- [GPT-5.3 Codex vs Kimi K2.5](/compare/gpt-5-3-codex-vs-kimi-k2-5)
- [Kimi K2.5 (Reasoning) vs Kimi K2.5](/compare/kimi-k2-5-vs-kimi-k2-5-reasoning)

## Explore More

- [GPT-5.3 Codex profile](/models/gpt-5-3-codex)
- [Kimi K2.5 (Reasoning) profile](/models/kimi-k2-5-reasoning)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)