# Claude Mythos 5 vs GPT-5.3 Codex

> Side-by-side benchmark comparison for Claude Mythos 5 and GPT-5.3 Codex across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/claude-mythos-5-vs-gpt-5-3-codex
- Last updated: September 4, 2026

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

## Quick Verdict

Pick Claude Mythos 5 if you want the stronger benchmark profile. GPT-5.3 Codex only makes more sense when its price, context window, or workload-specific category wins matter more than the overall score.

## Summary

- Claude Mythos 5 leads overall 85 to 65.22.
- The clearest category separation is in multimodal & grounded, where the averages are 85.1 for Claude Mythos 5 and 75.6 for GPT-5.3 Codex.
- The biggest single benchmark swing is SWE-bench Pro in Coding, with scores of 80.3% and 56.8%.
- GPT-5.3 Codex is the cheaper option on output tokens, which matters if you expect large responses or heavy interactive use.
- Claude Mythos 5 also has the larger context window at 1M+.

## Model Snapshot

| Property | Claude Mythos 5 | GPT-5.3 Codex |
|----------|----------|----------|
| Creator | Anthropic | OpenAI |
| Type | Proprietary | Proprietary |
| Reasoning | Reasoning | Reasoning |
| Context | 1M+ | 400K |
| Overall Score | null | 65.22 |
| Benchmarks Covered | 15 | 8 |
| Pricing (input/output) | $10.00 / $50.00 | $1.75 / $14.00 |

## Category Breakdown

### Agentic

- Winner: Coming soon
- Claude Mythos 5 public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 62.3 (Estimated · #19/151)

| Benchmark | Claude Mythos 5 | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.0 | 88% | 77.3% | Claude Mythos 5 |
| OSWorld-Verified | 85% | 64.7% | Claude Mythos 5 |
| BrowseComp | 88% | Coming soon | Coming soon |
| CyberGym | 83.8% | Coming soon | Coming soon |
| Gert Labs | Coming soon | 57.47% | Coming soon |
| JobBench | Coming soon | 33.7% | Coming soon |

### Coding

- Winner: Coming soon
- Claude Mythos 5 public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 62.7 (Supported · #16/183)

| Benchmark | Claude Mythos 5 | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | 95.5% | 85% | Claude Mythos 5 |
| SWE-bench Pro | 80.3% | 56.8% | Claude Mythos 5 |
| Terminal-Bench 2.0 | 88.0% | Coming soon | Coming soon |
| SWE-Rebench | Coming soon | 58.2% | Coming soon |
| Vibe Code Bench | Coming soon | 61.77% | Coming soon |

### Multimodal & Grounded

- Winner: Coming soon
- Claude Mythos 5 public-lane score: 85.1 (Unranked · 3 rankable rows)
- GPT-5.3 Codex public-lane score: 75.6 (Unranked · 1 rankable row)

| Benchmark | Claude Mythos 5 | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Multimodal | 54.9% | Coming soon | Coming soon |
| CharXiv | 93.5% | Coming soon | Coming soon |
| CharXiv w/o tools | 88.9% | Coming soon | Coming soon |

### Reasoning

- Winner: Coming soon
- Claude Mythos 5 public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 77.3 (Unranked · 2 rankable rows)

### Knowledge

- Winner: Coming soon
- Claude Mythos 5 public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 66.3 (Estimated · #22/181)

| Benchmark | Claude Mythos 5 | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| GPQA | 94.1% | Coming soon | Coming soon |
| HLE | 64.5% | Coming soon | Coming soon |
| HLE w/o tools | 59% | Coming soon | Coming soon |

### Instruction Following

- Winner: Coming soon
- Claude Mythos 5 public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 92.3 (#15/120)

### Multilingual

- Winner: Coming soon
- Claude Mythos 5 public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: Coming soon

| Benchmark | Claude Mythos 5 | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| SWE Multilingual | 92.2% | Coming soon | Coming soon |

### Mathematics

- Winner: Coming soon
- Claude Mythos 5 public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: Coming soon

| Benchmark | Claude Mythos 5 | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| USAMO 2026 | 97.6% | Coming soon | Coming soon |

## FAQ

### Which is better overall, Claude Mythos 5 or GPT-5.3 Codex?

Claude Mythos 5 is ahead overall on BenchLM right now.

### Where is the biggest gap between Claude Mythos 5 and GPT-5.3 Codex?

The widest category gap is in multimodal & grounded, where the averages are 85.1 for Claude Mythos 5 and 75.6 for GPT-5.3 Codex.

### How many benchmarks does Claude Mythos 5 cover on BenchLM?

Claude Mythos 5 currently has 15 sourced benchmark scores on BenchLM.

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

GPT-5.3 Codex currently has 8 sourced benchmark scores on BenchLM.

## Related Comparisons

- [Claude Mythos 5 vs Claude Mythos 5.1](/compare/claude-mythos-5-vs-claude-mythos-5-1)
- [GPT-5.3 Codex vs Claude Mythos 5.1](/compare/claude-mythos-5-1-vs-gpt-5-3-codex)
- [Claude Mythos 5 vs Claude Mythos Preview](/compare/claude-mythos-5-vs-claude-mythos-preview)
- [GPT-5.3 Codex vs Claude Mythos Preview](/compare/claude-mythos-preview-vs-gpt-5-3-codex)

## Explore More

- [Claude Mythos 5 profile](/models/claude-mythos-5)
- [GPT-5.3 Codex profile](/models/gpt-5-3-codex)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)