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Model Comparison

Claude Mythos Preview vs GPT-5.3 CodexWhich is better in 2026?

Claude Mythos Preview significantly outperforms across most benchmarks. GPT-5.3 Codex is 10.4x cheaper per token.

Verdict: Claude Mythos Preview vs GPT-5.3 Codex — which is better?

Claude Mythos Preview (by Anthropic) and GPT-5.3 Codex (by OpenAI) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.

Claude Mythos Preview outperforms in 3 benchmarks (OSWorld-Verified, SWE-Bench Pro, Terminal-Bench 2.0), while GPT-5.3 Codex is better at 0 benchmarks. Claude Mythos Preview significantly outperforms across most benchmarks.

On price, GPT-5.3 Codex is roughly 10.4x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Choose Claude Mythos Preview if…

  • you want the strongest raw capability — it leads on 3 of 3 shared benchmarks

Choose GPT-5.3 Codex if…

  • cost matters — it's about 10.4x cheaper per token

Performance Benchmarks

Comparative analysis across standard metrics

3 benchmarks

Claude Mythos Preview outperforms in 3 benchmarks (OSWorld-Verified, SWE-Bench Pro, Terminal-Bench 2.0), while GPT-5.3 Codex is better at 0 benchmarks.

Claude Mythos Preview significantly outperforms across most benchmarks.

Thu Aug 06 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

GPT-5.3 Codex costs less

For input processing, Claude Mythos Preview ($25.00/1M tokens) is 14.3x more expensive than GPT-5.3 Codex ($1.75/1M tokens).

For output processing, Claude Mythos Preview ($125.00/1M tokens) is 8.9x more expensive than GPT-5.3 Codex ($14.00/1M tokens).

In conclusion, Claude Mythos Preview is more expensive than GPT-5.3 Codex.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers
Thu Aug 06 2026 • llm-stats.com
Anthropic
Claude Mythos Preview
Input tokens$25.00
Output tokens$125.00
Best providerAnthropic
OpenAI
GPT-5.3 Codex
Input tokens$1.75
Output tokens$14.00
Best providerOpenAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Only GPT-5.3 Codex specifies input context (400,000 tokens). Only GPT-5.3 Codex specifies output context (128,000 tokens).

Anthropic
Claude Mythos Preview
Input- tokens
Output- tokens
OpenAI
GPT-5.3 Codex
Input400,000 tokens
Output128,000 tokens
Thu Aug 06 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Claude Mythos Preview and GPT-5.3 Codex support multimodal inputs.

They are both capable of processing various types of data, offering versatility in application.

Claude Mythos Preview

Text
Images
Audio
Video

GPT-5.3 Codex

Text
Images
Audio
Video

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

Claude Mythos Preview

Proprietary

Closed source

GPT-5.3 Codex

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.3 Codex was released on 2026-02-05, while Claude Mythos Preview's release date is not specified.

We can confirm GPT-5.3 Codex's release timeline, but cannot make a direct age comparison without Claude Mythos Preview's release date.

Claude Mythos Preview

—

GPT-5.3 Codex

Feb 5, 2026

6 months ago

Knowledge Cutoff

When training data ends

Neither model specifies a knowledge cutoff date.

Unable to compare the recency of their training data.

No cutoff dates available

Provider Availability

Claude Mythos Preview is available from Anthropic. GPT-5.3 Codex is available from OpenAI.

Claude Mythos Preview

anthropic logo
Anthropic
Input Price:Input: $25.00/1MOutput Price:Output: $125.00/1M

GPT-5.3 Codex

openai logo
OpenAI
Input Price:Input: $1.75/1MOutput Price:Output: $14.00/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

Anthropic
Higher OSWorld-Verified score (79.6% vs 64.7%)
Higher SWE-Bench Pro score (77.8% vs 56.8%)
Higher Terminal-Bench 2.0 score (82.0% vs 77.3%)
OpenAI
Larger context window (400,000 tokens)
Less expensive input tokens
Less expensive output tokens

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against Claude Mythos Preview and GPT-5.3 Codex side-by-side, then vote on the output you prefer.

Claude Mythos Preview
✓ Preferred
GPT-5.3 Codex
Open in Playground
AI Model Comparison Table
Feature
Anthropic
Claude Mythos Preview
OpenAI
GPT-5.3 Codex

FAQ

Common questions about Claude Mythos Preview vs GPT-5.3 Codex.

Which is better, Claude Mythos Preview or GPT-5.3 Codex?

Claude Mythos Preview significantly outperforms across most benchmarks. Claude Mythos Preview is made by Anthropic and GPT-5.3 Codex is made by OpenAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does Claude Mythos Preview compare to GPT-5.3 Codex in benchmarks?

Claude Mythos Preview scores CyBench: 100.0%, USAMO25: 97.6%, GPQA: 94.6%, SWE-Bench Verified: 93.9%, CharXiv-R: 93.2%. GPT-5.3 Codex scores SWE-Lancer (IC-Diamond subset): 81.4%, Cybersecurity CTFs: 77.6%, Terminal-Bench 2.0: 77.3%, LiveBench: 72.8%, OSWorld-Verified: 64.7%.

Is Claude Mythos Preview cheaper than GPT-5.3 Codex?

GPT-5.3 Codex is 14.3x cheaper for input tokens. Claude Mythos Preview costs $25.00/M input and $125.00/M output via anthropic. GPT-5.3 Codex costs $1.75/M input and $14.00/M output via openai.

What are the context window sizes for Claude Mythos Preview and GPT-5.3 Codex?

Claude Mythos Preview supports an unknown number of tokens and GPT-5.3 Codex supports 400K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between Claude Mythos Preview and GPT-5.3 Codex?

Key differences include input pricing ($25.00 vs $1.75/M). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Mythos Preview and GPT-5.3 Codex?

Claude Mythos Preview is developed by Anthropic and GPT-5.3 Codex is developed by OpenAI.

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