Claude Sonnet 4.5 vs GPT-5.1 Codex
Side-by-side benchmark comparison across coding, math, reasoning, speed, and pricing.
GPT-5.1 Codex by OpenAI wins on 11 of 16 benchmarks against Claude Sonnet 4.5 by Anthropic, which leads on 5. 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, GPT-5.1 Codex scores 1395 on Chatbot Arena ELO compared to Claude Sonnet 4.5's 1380, while Claude Sonnet 4.5 scores 83.0% 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 Claude Sonnet 4.5's 90.0%, while GPT-5.1 Codex scores 78.0% on SWE-bench Verified compared to Claude Sonnet 4.5's 77.2%, while GPT-5.1 Codex scores 85.0% on LiveCodeBench compared to Claude Sonnet 4.5's 62.0%, while GPT-5.1 Codex scores 76.0% on Aider Polyglot compared to Claude Sonnet 4.5's 68.0%.
Math: In math, Claude Sonnet 4.5 scores 87.0% on MATH compared to GPT-5.1 Codex's 85.0%, while Claude Sonnet 4.5 scores 95.5% on GSM8K compared to GPT-5.1 Codex's 95.0%.
Reasoning: In reasoning, Claude Sonnet 4.5 scores 83.4% 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 Claude Sonnet 4.5's 45.0%.
Context: In context, Claude Sonnet 4.5 scores 1.0M on Context Length compared to GPT-5.1 Codex's 400K.
Pricing Comparison
Claude Sonnet 4.5 costs $3.0/1M input tokens and $15.0/1M 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.
Speed Comparison
Claude Sonnet 4.5 generates output at 67 tok/s compared to GPT-5.1 Codex's 85 tok/s, and the time to first token is 1170 ms for Claude Sonnet 4.5 versus 400 ms for GPT-5.1 Codex. GPT-5.1 Codex delivers faster throughput.
Verdict
For developers prioritizing math, Claude Sonnet 4.5 has the edge. For those who value coding and general intelligence and affordability and speed, GPT-5.1 Codex is the stronger choice.
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Claude Sonnet 4.5 vs GPT-5.1 Codex — FAQ
Which is better, Claude Sonnet 4.5 or GPT-5.1 Codex?
GPT-5.1 Codex wins on more benchmarks overall (11 vs 5). However, the best choice depends on your specific needs — each model excels in different areas.
How does Claude Sonnet 4.5 compare to GPT-5.1 Codex for coding?
GPT-5.1 Codex is better for coding, scoring 78.0% on SWE-bench Verified compared to 77.2%. SWE-bench tests real-world software engineering by resolving actual GitHub issues.
Is Claude Sonnet 4.5 cheaper than GPT-5.1 Codex?
Yes, GPT-5.1 Codex is cheaper. Claude Sonnet 4.5 costs $3.0/1M input and $15.0/1M output tokens. GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output tokens.
Which is faster, Claude Sonnet 4.5 or GPT-5.1 Codex?
GPT-5.1 Codex is faster, generating output at 85 tok/s compared to 67 tok/s. Faster output speed means shorter wait times for API responses.
What benchmarks does the Claude Sonnet 4.5 vs GPT-5.1 Codex comparison cover?
This comparison covers 16 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.