Gemini 3 Flash vs GPT-5.1 Codex
Side-by-side benchmark comparison across coding, math, reasoning, speed, and pricing.
Gemini 3 Flash by Google wins on 9 of 15 benchmarks against GPT-5.1 Codex by OpenAI, which leads on 3. This head-to-head comparison covers coding, math, reasoning, speed, and pricing metrics from our benchmark data.
Category-by-Category Breakdown
General Intelligence: In general intelligence, Gemini 3 Flash scores 1473 on Chatbot Arena ELO compared to GPT-5.1 Codex's 1395, while Gemini 3 Flash scores 88.6% on MMLU-Pro compared to GPT-5.1 Codex's 82.0%.
Coding: In coding, GPT-5.1 Codex scores 96.0% on HumanEval+ compared to Gemini 3 Flash's 86.0%, while both score 78.0% on SWE-bench Verified, while GPT-5.1 Codex scores 85.0% on LiveCodeBench compared to Gemini 3 Flash's 55.0%.
Math: In math, both score 85.0% on MATH, while both score 95.0% on GSM8K.
Reasoning: In reasoning, Gemini 3 Flash scores 72.0% on GPQA Diamond compared to GPT-5.1 Codex's 65.0%, while GPT-5.1 Codex scores 52.0% on ARC-AGI compared to Gemini 3 Flash's 30.0%.
Context: In context, Gemini 3 Flash scores 1.0M on Context Length compared to GPT-5.1 Codex's 400K.
Pricing Comparison
Gemini 3 Flash costs $0.50/1M input tokens and $3.0/1M output tokens, while GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output. Gemini 3 Flash is the more affordable option for API usage.
Speed Comparison
Gemini 3 Flash generates output at 200 tok/s compared to GPT-5.1 Codex's 85 tok/s, and the time to first token is 100 ms for Gemini 3 Flash versus 400 ms for GPT-5.1 Codex. Gemini 3 Flash delivers faster throughput.
Verdict
Gemini 3 Flash leads across the board in general intelligence, affordability, speed, making it the stronger overall choice in this comparison.
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Gemini 3 Flash vs GPT-5.1 Codex — FAQ
Which is better, Gemini 3 Flash or GPT-5.1 Codex?
Gemini 3 Flash wins on more benchmarks overall (9 vs 3). However, the best choice depends on your specific needs — each model excels in different areas.
How does Gemini 3 Flash compare to GPT-5.1 Codex for coding?
Both models score 78.0% on SWE-bench Verified, making them equally capable for coding tasks.
Is Gemini 3 Flash cheaper than GPT-5.1 Codex?
Yes, Gemini 3 Flash is cheaper. Gemini 3 Flash costs $0.50/1M input and $3.0/1M output tokens. GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output tokens.
Which is faster, Gemini 3 Flash or GPT-5.1 Codex?
Gemini 3 Flash is faster, generating output at 200 tok/s compared to 85 tok/s. Faster output speed means shorter wait times for API responses.
What benchmarks does the Gemini 3 Flash vs GPT-5.1 Codex comparison cover?
This comparison covers 15 benchmarks including Chatbot Arena ELO, MMLU-Pro, HumanEval+, MATH, GPQA Diamond, SWE-bench Verified, Output Speed, LiveCodeBench, and more. Metrics span general intelligence, coding, math, reasoning, speed, and cost categories.