Claude Opus 4.5 vs GPT-5.1 Codex
Wins 5 of 7 areas
Coding · Agents · Facts · Images and charts · Long documents
Wins 1 of 7 areas
Following instructions
Claude Opus 4.5 is the stronger all-rounder.GPT-5.1 Codex is cheaper and better at following instructions.
Scores updated · 20 tests both models report · How we compare
Where each one wins
Tests won in each of the seven areas where both have results. Each piece is one test, so a longer bar means more evidence; grey means the two scored within a point of each other.
- CodingWriting and fixing software40Claude Opus 4.54 of 4 tests
- FactsGetting facts right instead of making them up20Claude Opus 4.52 of 2 tests
- AgentsCarrying out multi-step tasks on its own10Claude Opus 4.51 of 1 test
- Images and chartsUnderstanding pictures, charts and video10Claude Opus 4.51 of 1 test
- Long documentsFinding answers in very long texts10Claude Opus 4.51 of 1 test
- Following instructionsDoing exactly what it is asked01GPT-5.1 Codex1 of 1 test
- ReasoningHard problems that need careful thinking11Even1 each · 1 tie
Agents, images and charts, long documents and following instructions rest on a single test each.
What it costs
Prices per million tokens, roughly 750,000 words. The bars show the cost of a million tokens read plus a million written.
GPT-5.1 Codex costs 63% less for the same work.
The biggest differences
The tests each model wins by the widest margin, up to three each. Scores are out of 100.
Where Claude Opus 4.5 pulls ahead
- Avoids making up answers it doesn't knowAA-Omniscience · Non-hallucination+16.2points ahead
- Real work tasks from 44 professionsGDPVal+12.7points ahead
- Hard command-line tasks in a real terminalTerminal-Bench Hard+12.2points ahead
Every test, side by side
All 20 tests both models report. The winning score is in its model's colour; marks a score checked independently.
CodingClaude Opus 4.5
- LMArena · WebDevClaude Opus 4.5 by 132 rating points14681336+132 rating
- Terminal-Bench HardClaude Opus 4.5 by 12.24734.8+12.2
- SciCodeClaude Opus 4.5 by 9.349.540.2+9.3
- SWE-bench VerifiedClaude Opus 4.5 by 7.280.973.7+7.2
ReasoningEven
- Humanity's Last ExamClaude Opus 4.5 by 4.430.125.7+4.4
- CritPtGPT-5.1 Codex by 1.14.65.7+1.1
- GPQA Diamondtie86.686tie
FactsClaude Opus 4.5
- AA-Omniscience · Non-hallucinationClaude Opus 4.5 by 16.23922.8+16.2
- AA-Omniscience · AccuracyClaude Opus 4.5 by 6.746.639.9+6.7
Images and chartsClaude Opus 4.5
- MMMU-ProClaude Opus 4.5 by 1.57472.5+1.5
Following instructionsGPT-5.1 Codex
- IFBenchGPT-5.1 Codex by 125870+12
Other results7 tests, not counted
Tests outside the eight areas. They are not counted above: several are summary scores built from other tests, or the same test under another name.
- AA-OmniscienceClaude Opus 4.5 by 20.514-6.5+20.5
- Artificial Analysis Coding IndexClaude Opus 4.5 by 11.247.836.6+11.2
- AA Agentic IndexClaude Opus 4.5 by 8.959.650.7+8.9
- swe_bench_bashClaude Opus 4.5 by 8.474.466+8.4
- Terminal-Bench 2.0Claude Opus 4.5 by 6.559.352.8+6.5
- τ²-Bench Telecom (AA run)Claude Opus 4.5 by 6.589.583+6.5
- AA IntelligenceClaude Opus 4.5 by 5.429.123.7+5.4
Questions people ask
Which is better, Claude Opus 4.5 or GPT-5.1 Codex?
Claude Opus 4.5 wins five of the seven areas where both have results: coding, agents, facts, images and charts and long documents. GPT-5.1 Codex wins following instructions, and costs 63% less. They are level on reasoning.
Which is better for coding?
Claude Opus 4.5. It wins 4 of the 4 coding tests both models report; GPT-5.1 Codex wins none.
Which is cheaper?
Claude Opus 4.5 costs $5.00 per million input tokens and $25.00 per million output tokens; GPT-5.1 Codex costs $1.25 and $10.00. That makes GPT-5.1 Codex about 63% cheaper for the same work.
How do you compare the two?
We use the 20 benchmark tests both models have published scores on. The verdict counts the 13 tests in the eight capability areas, and a gap under one point (ten on rating-style scales) counts as a tie. The other 7 are listed but not counted, because several are summary scores or repeat a test. Each score is the one shown on the model's own page.