# Claude Mythos Preview vs GPT-5.3 Codex

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

- Canonical page: https://benchlm.ai/compare/claude-mythos-preview-vs-gpt-5-3-codex
- Last updated: September 29, 2026

- Shared sourced benchmarks: 0
- HTML indexing: indexable
- Ranking lane: BenchAlign v5.7

## Quick Verdict

No benchmark verdict yet: there is no shared sourced benchmark row for Claude Mythos Preview and GPT-5.3 Codex.

## Summary

- Claude Mythos Preview and GPT-5.3 Codex do not currently share a sourced benchmark row. The mirror therefore compares metadata, pricing, context windows, and each model's separately reported coverage without naming a benchmark winner.

## Model Snapshot

| Property | Claude Mythos Preview | GPT-5.3 Codex |
|----------|----------|----------|
| Creator | Anthropic | OpenAI |
| Type | Proprietary | Proprietary |
| Reasoning | Reasoning | Reasoning |
| Context | null | 400K |
| Independent public score (not head-to-head) | null | 61.81 |
| Benchmarks Covered | 2 | 10 |
| Pricing (input/output) | $25.00 / $125.00 | $1.75 / $14.00 |

## Category Breakdown

### Agentic

- Winner: Insufficient shared evidence
- Claude Mythos Preview public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 54.1 (Estimated · #34/117)

| Benchmark | Claude Mythos Preview | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| CyberGym | 83.1% | Coming soon | Coming soon |
| ExploitGym | 17.5% | Coming soon | Coming soon |
| Terminal-Bench 2.0 | Coming soon | 77.3% | Coming soon |
| OSWorld-Verified | Coming soon | 64.7% | Coming soon |
| Gert Labs | Coming soon | 57.47% | Coming soon |
| JobBench | Coming soon | 33.7% | Coming soon |

### Coding

- Winner: Insufficient shared evidence
- Claude Mythos Preview public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 55.5 (Supported · #29/143)

| Benchmark | Claude Mythos Preview | GPT-5.3 Codex | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | Coming soon | 85% | Coming soon |
| SWE-bench Pro | Coming soon | 56.8% | Coming soon |
| SWE-Rebench | Coming soon | 58.2% | Coming soon |
| Vibe Code Bench | Coming soon | 61.77% | Coming soon |
| LiveCodeBench (Vals) | Coming soon | 87.3% | Coming soon |
| SWE-bench (Vals) | Coming soon | 78.0% | Coming soon |

### Reasoning

- Winner: Insufficient shared evidence
- Claude Mythos Preview public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 79.6 (Unranked · 2 rankable rows)

### Multimodal & Grounded

- Winner: Insufficient shared evidence
- Claude Mythos Preview public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 76.7 (Unranked · 1 rankable row)

### Knowledge

- Winner: Insufficient shared evidence
- Claude Mythos Preview public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 63.8 (Estimated · #31/169)

### Instruction Following

- Winner: Insufficient shared evidence
- Claude Mythos Preview public-lane score: Coming soon
- GPT-5.3 Codex public-lane score: 91.2 (#14/124)

## FAQ

### Can I compare Claude Mythos Preview and GPT-5.3 Codex on BenchLM yet?

Not fully yet. BenchLM is tracking both models, but sourced benchmark coverage is still incomplete for a fair score-level comparison.

### Why does this page show "coming soon" values?

BenchLM only calls winners when public benchmark coverage is available on both sides of the comparison.

## Related Comparisons

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

## Explore More

- [Claude Mythos Preview profile](/models/claude-mythos-preview)
- [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)