GPT-5.1 Codex vs GPT-OSS 120B
Side-by-side benchmark comparison across coding, math, reasoning, speed, and pricing.
GPT-5.1 Codex by OpenAI and GPT-OSS 120B by OpenAI are evenly matched across 8 benchmarks. 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 120B's 974, while GPT-5.1 Codex scores 1174 on Website Arena ELO compared to GPT-OSS 120B's 980.
Reasoning: In reasoning, GPT-OSS 120B scores 74.9% 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 120B's 131K.
Pricing Comparison
GPT-5.1 Codex costs $1.3/1M input tokens and $10.0/1M output tokens, while GPT-OSS 120B costs $0.04/1M input and $0.17/1M output. GPT-OSS 120B is the more affordable option for API usage.
Speed Comparison
GPT-5.1 Codex generates output at 85 tok/s compared to GPT-OSS 120B's 339 tok/s, and the time to first token is 400 ms for GPT-5.1 Codex versus 440 ms for GPT-OSS 120B. GPT-OSS 120B delivers faster throughput.
Verdict
GPT-OSS 120B leads across the board in affordability, speed, making it the stronger overall choice in this comparison.
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GPT-5.1 Codex vs GPT-OSS 120B — FAQ
Which is better, GPT-5.1 Codex or GPT-OSS 120B?
GPT-5.1 Codex and GPT-OSS 120B are evenly matched across benchmarks. The best choice depends on your specific priorities such as coding ability, speed, or pricing.
How does GPT-5.1 Codex compare to GPT-OSS 120B 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 120B?
Yes, GPT-OSS 120B is cheaper. GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output tokens. GPT-OSS 120B costs $0.04/1M input and $0.17/1M output tokens.
Which is faster, GPT-5.1 Codex or GPT-OSS 120B?
GPT-OSS 120B is faster, generating output at 339 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 120B comparison cover?
This comparison covers 8 benchmarks including GPQA Diamond, Output Speed, Time to First Token, Input Cost, Output Cost, Context Length, Design Arena ELO, Website Arena ELO. Metrics span general intelligence, coding, math, reasoning, speed, and cost categories.