Gemini 3.5 Flash vs GPT-5.1 Codex
Side-by-side benchmark comparison across coding, math, reasoning, speed, and pricing.
Gemini 3.5 Flash by Google wins on 5 of 7 benchmarks against GPT-5.1 Codex by OpenAI, which leads on 2. This head-to-head comparison covers coding, math, reasoning, speed, and pricing metrics from our benchmark data.
Category-by-Category Breakdown
Coding: In coding, Gemini 3.5 Flash scores 1275 on Design Arena ELO compared to GPT-5.1 Codex's 1197, while Gemini 3.5 Flash scores 1275 on Website Arena ELO compared to GPT-5.1 Codex's 1174.
Reasoning: In reasoning, Gemini 3.5 Flash scores 92.8% on GPQA Diamond compared to GPT-5.1 Codex's 65.0%.
Context: In context, Gemini 3.5 Flash scores 1.0M on Context Length compared to GPT-5.1 Codex's 400K.
Pricing Comparison
Gemini 3.5 Flash costs $1.5/1M input tokens and $9.0/1M output tokens, while GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output. GPT-5.1 Codex is the more affordable option for API usage.
Verdict
GPT-5.1 Codex leads across the board in affordability, making it the stronger overall choice in this comparison.
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Gemini 3.5 Flash vs GPT-5.1 Codex — FAQ
Which is better, Gemini 3.5 Flash or GPT-5.1 Codex?
Gemini 3.5 Flash wins on more benchmarks overall (5 vs 2). However, the best choice depends on your specific needs — each model excels in different areas.
How does Gemini 3.5 Flash compare to GPT-5.1 Codex for coding?
SWE-bench Verified data is not available for both models. Check the detailed comparison charts above for other coding-related metrics.
Is Gemini 3.5 Flash cheaper than GPT-5.1 Codex?
Yes, GPT-5.1 Codex is cheaper. Gemini 3.5 Flash costs $1.5/1M input and $9.0/1M output tokens. GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output tokens.
Which is faster, Gemini 3.5 Flash or GPT-5.1 Codex?
Output speed data is not available for both models. Check the speed section of the comparison above for available performance data.
What benchmarks does the Gemini 3.5 Flash vs GPT-5.1 Codex comparison cover?
This comparison covers 7 benchmarks including GPQA Diamond, Input Cost, Output Cost, Context Length, Cached Input Cost, Design Arena ELO, Website Arena ELO. Metrics span general intelligence, coding, math, reasoning, speed, and cost categories.