GPT-5.1 Codex vs GPT-OSS 20B
Side-by-side benchmark comparison across coding, math, reasoning, speed, and pricing.
GPT-OSS 20B by OpenAI wins on 5 of 9 benchmarks against GPT-5.1 Codex by OpenAI, which leads on 4. This head-to-head comparison covers coding, math, reasoning, speed, and pricing metrics from our benchmark data.
Category-by-Category Breakdown
Coding: In coding, GPT-5.1 Codex scores 1197 on Design Arena ELO compared to GPT-OSS 20B's 906, while GPT-5.1 Codex scores 1174 on Website Arena ELO compared to GPT-OSS 20B's 865.
Reasoning: In reasoning, GPT-OSS 20B scores 66.5% on GPQA Diamond compared to GPT-5.1 Codex's 65.0%.
Context: In context, GPT-5.1 Codex scores 400K on Context Length compared to GPT-OSS 20B's 131K.
Pricing Comparison
GPT-5.1 Codex costs $1.3/1M input tokens and $10.0/1M output tokens, while GPT-OSS 20B costs $0.03/1M input and $0.13/1M output. GPT-OSS 20B is the more affordable option for API usage.
Speed Comparison
GPT-5.1 Codex generates output at 85 tok/s compared to GPT-OSS 20B's 312 tok/s, and the time to first token is 400 ms for GPT-5.1 Codex versus 470 ms for GPT-OSS 20B. GPT-OSS 20B delivers faster throughput.
Verdict
GPT-OSS 20B leads across the board in affordability, speed, making it the stronger overall choice in this comparison.
View Individual Model Pages
GPT-5.1 Codex vs GPT-OSS 20B — FAQ
Which is better, GPT-5.1 Codex or GPT-OSS 20B?
GPT-OSS 20B wins on more benchmarks overall (5 vs 4). However, the best choice depends on your specific needs — each model excels in different areas.
How does GPT-5.1 Codex compare to GPT-OSS 20B for coding?
SWE-bench Verified data is not available for both models. Check the detailed comparison charts above for other coding-related metrics.
Is GPT-5.1 Codex cheaper than GPT-OSS 20B?
Yes, GPT-OSS 20B is cheaper. GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output tokens. GPT-OSS 20B costs $0.03/1M input and $0.13/1M output tokens.
Which is faster, GPT-5.1 Codex or GPT-OSS 20B?
GPT-OSS 20B is faster, generating output at 312 tok/s compared to 85 tok/s. Faster output speed means shorter wait times for API responses.
What benchmarks does the GPT-5.1 Codex vs GPT-OSS 20B comparison cover?
This comparison covers 9 benchmarks including GPQA Diamond, Output Speed, Time to First Token, Input Cost, Output Cost, Context Length, Cached Input Cost, Design Arena ELO, and more. Metrics span general intelligence, coding, math, reasoning, speed, and cost categories.