Model Comparison

GPT-5 Codex vs GPT OSS 20B

Comparing GPT-5 Codex and GPT OSS 20B across benchmarks, pricing, and capabilities.

Want to compare interactively?Try the playground

Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

GPT-5 Codex and GPT OSS 20B don't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Arena Performance

Human preference votes

Context Window

Maximum input and output token capacity

Only GPT OSS 20B specifies input context (131,072 tokens). Only GPT OSS 20B specifies output context (32,768 tokens).

OpenAI
GPT-5 Codex
Input- tokens
Output- tokens
OpenAI
GPT OSS 20B
Input131,072 tokens
Output32,768 tokens
Fri May 15 2026 • llm-stats.com

License

Usage and distribution terms

GPT-5 Codex is licensed under a proprietary license, while GPT OSS 20B uses Apache 2.0.

License differences may affect how you can use these models in commercial or open-source projects.

GPT-5 Codex

Proprietary

Closed source

GPT OSS 20B

Apache 2.0

Open weights

Release Timeline

When each model was launched

GPT-5 Codex was released on 2025-09-15, while GPT OSS 20B was released on 2025-08-05.

GPT-5 Codex is 1 month newer than GPT OSS 20B.

GPT-5 Codex

Sep 15, 2025

8 months ago

1mo newer
GPT OSS 20B

Aug 5, 2025

9 months ago

Knowledge Cutoff

When training data ends

GPT-5 Codex has a documented knowledge cutoff of 2024-09-30, while GPT OSS 20B's cutoff date is not specified.

We can confirm GPT-5 Codex's training data extends to 2024-09-30, but cannot make a direct comparison without GPT OSS 20B's cutoff date.

GPT-5 Codex

Sep 2024

GPT OSS 20B

—

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

OpenAI

No standout differentiators in the data we have for this pair.

OpenAI
Larger context window (131,072 tokens)
Has open weights

Detailed Comparison

AI Model Comparison Table
Feature
OpenAI
GPT-5 Codex
OpenAI
GPT OSS 20B

FAQ

Common questions about GPT-5 Codex vs GPT OSS 20B.

Which is better, GPT-5 Codex or GPT OSS 20B?

GPT-5 Codex (OpenAI) and GPT OSS 20B (OpenAI) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

How does GPT-5 Codex compare to GPT OSS 20B in benchmarks?

GPT-5 Codex scores SWE-Bench Verified: 74.5%. GPT OSS 20B scores MMLU: 85.3%, CodeForces: 74.3%, GPQA: 71.5%, TAU-bench Retail: 54.8%, HealthBench: 42.5%.

What are the context window sizes for GPT-5 Codex and GPT OSS 20B?

GPT-5 Codex supports an unknown number of tokens and GPT OSS 20B supports 131K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-5 Codex and GPT OSS 20B?

Key differences include licensing (Proprietary vs Apache 2.0). See the full comparison above for benchmark-by-benchmark results.