Claude Opus 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 9 of 16 benchmarks against Claude Opus 4.5 by Anthropic, which leads on 7. 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, Claude Opus 4.5 scores 1468 on Chatbot Arena ELO compared to GPT-5.1 Codex's 1395, while Claude Opus 4.5 scores 89.5% 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 Opus 4.5's 92.0%, while Claude Opus 4.5 scores 80.9% on SWE-bench Verified compared to GPT-5.1 Codex's 78.0%, while GPT-5.1 Codex scores 85.0% on LiveCodeBench compared to Claude Opus 4.5's 70.0%, while GPT-5.1 Codex scores 76.0% on Aider Polyglot compared to Claude Opus 4.5's 74.0%.
Math: In math, Claude Opus 4.5 scores 90.0% on MATH compared to GPT-5.1 Codex's 85.0%, while Claude Opus 4.5 scores 96.5% on GSM8K compared to GPT-5.1 Codex's 95.0%.
Reasoning: In reasoning, Claude Opus 4.5 scores 87.0% on GPQA Diamond compared to GPT-5.1 Codex's 65.0%, while Claude Opus 4.5 scores 57.0% on ARC-AGI compared to GPT-5.1 Codex's 52.0%.
Context: In context, GPT-5.1 Codex scores 400K on Context Length compared to Claude Opus 4.5's 200K.
Pricing Comparison
Claude Opus 4.5 costs $5.0/1M input tokens and $25.0/1M 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 Opus 4.5 generates output at 50 tok/s compared to GPT-5.1 Codex's 85 tok/s, and the time to first token is 1700 ms for Claude Opus 4.5 versus 400 ms for GPT-5.1 Codex. GPT-5.1 Codex delivers faster throughput.
Verdict
For developers prioritizing coding and general intelligence and math, Claude Opus 4.5 has the edge. For those who value affordability and speed, GPT-5.1 Codex is the stronger choice.
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Claude Opus 4.5 vs GPT-5.1 Codex — FAQ
Which is better, Claude Opus 4.5 or GPT-5.1 Codex?
GPT-5.1 Codex wins on more benchmarks overall (9 vs 7). However, the best choice depends on your specific needs — each model excels in different areas.
How does Claude Opus 4.5 compare to GPT-5.1 Codex for coding?
Claude Opus 4.5 is better for coding, scoring 80.9% on SWE-bench Verified compared to 78.0%. SWE-bench tests real-world software engineering by resolving actual GitHub issues.
Is Claude Opus 4.5 cheaper than GPT-5.1 Codex?
Yes, GPT-5.1 Codex is cheaper. Claude Opus 4.5 costs $5.0/1M input and $25.0/1M output tokens. GPT-5.1 Codex costs $1.3/1M input and $10.0/1M output tokens.
Which is faster, Claude Opus 4.5 or GPT-5.1 Codex?
GPT-5.1 Codex is faster, generating output at 85 tok/s compared to 50 tok/s. Faster output speed means shorter wait times for API responses.
What benchmarks does the Claude Opus 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.