GPT-5.1 Codex High vs GPT OSS 20B High: Specs & Benchmark Comparison
GPT-5.1 Codex High and GPT OSS 20B High both come from OpenAI, GPT OSS 20B High was released in October 2025, and GPT-5.1 Codex High followed a month later in November 2025. GPT OSS 20B High has a published size of about 20 billion parameters; OpenAI has not disclosed the parameter count of GPT-5.1 Codex High.
We have 1 benchmark result for GPT-5.1 Codex High and 2 benchmark results for GPT OSS 20B High, but they overlap on a single test: AIME 2025, where GPT OSS 20B High scores 98.7% against 97.0%.
GPT OSS 20B High is the cheaper API at $0.10 per million input tokens and $0.50 per million output tokens, roughly 13 times cheaper than GPT-5.1 Codex High at $1.25 and $10. GPT-5.1 Codex High takes the larger context window at 400K tokens, compared with 131K for GPT OSS 20B High. GPT-5.1 Codex High accepts text and images as input, while GPT OSS 20B High accepts text.
| Characteristic | GPT-5.1 Codex High | GPT OSS 20B High |
|---|---|---|
| Company | OpenAI | OpenAI |
| Release Date | November 11, 2025 | October 1, 2025 |
| Parameters | — | 20B |
| Multimodal | Yes | No |
| Context (input) | 400K | 131K |
| Context (output) | 128K | 131K |
| Input Price / 1M | $1.25 | $0.10 |
| Output Price / 1M | $10.00 | $0.50 |
| Average Score | 97.0% | 86.5% |
| Benchmarks | ||
| AIME 2025 | 97.0% | 98.7% |
Visual Benchmark Comparison
Verdict
GPT-5.1 Codex High leads in 2 out of 4 comparison categories.
Both models show comparable average scores: GPT-5.1 Codex High — 1.0, GPT OSS 20B High — 0.9.
GPT OSS 20B High is 18.8x cheaper: input $0.10/1M vs $1.25/1M tokens.
GPT-5.1 Codex High supports a larger context: 400K vs 131K tokens.
GPT-5.1 Codex High is newer: released 11/11/2025 vs 10/1/2025.
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Frequently Asked Questions
Which is better for coding — GPT-5.1 Codex High or GPT OSS 20B High?
Which model is cheaper — GPT-5.1 Codex High or GPT OSS 20B High?
Which has a larger context window — GPT-5.1 Codex High or GPT OSS 20B High?
The GPT-5.1 Codex High and GPT OSS 20B High comparison is updated for 2026. Data includes benchmark results, API pricing, context window size and other specifications. For more detailed information, visit the GPT-5.1 Codex High or GPT OSS 20B High page. See also the complete list of AI model comparisons.