GPT-5.1 vs GPT-5.1 Codex
Wins 5 of 7 areas
Coding · Reasoning · Images and charts · Long documents · Following instructions
Wins 1 of 7 areas
Agents
GPT-5.1 is the stronger all-rounder.GPT-5.1 Codex is better at agents.
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 software40GPT-5.14 of 4 tests
- ReasoningHard problems that need careful thinking20GPT-5.12 of 3 tests · 1 tie
- Images and chartsUnderstanding pictures, charts and video10GPT-5.11 of 1 test
- Long documentsFinding answers in very long texts10GPT-5.11 of 1 test
- Following instructionsDoing exactly what it is asked10GPT-5.11 of 1 test
- AgentsCarrying out multi-step tasks on its own01GPT-5.1 Codex1 of 1 test
- FactsGetting facts right instead of making them up11Even1 each
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.
The biggest differences
The tests each model wins by the widest margin, up to three each. Scores are out of 100.
Where GPT-5.1 pulls ahead
- Avoids making up answers it doesn't knowAA-Omniscience · Non-hallucination+25.3points ahead
- Hard command-line tasks in a real terminalTerminal-Bench Hard+10.7points ahead
- Reasons across sets of long documentsAA-LCR+10.7points ahead
Where GPT-5.1 Codex pulls ahead
- Real work tasks from 44 professionsGDPVal+18.1points ahead
- Answers hard knowledge questions correctlyAA-Omniscience · Accuracy+2.2points 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.
CodingGPT-5.1
- Terminal-Bench HardGPT-5.1 by 10.745.534.8+10.7
- LMArena · WebDevGPT-5.1 by 59 rating points13951336+59 rating
- SciCodeGPT-5.1 by 3.143.340.2+3.1
- SWE-bench VerifiedGPT-5.1 by 2.676.373.7+2.6
ReasoningGPT-5.1
- Humanity's Last ExamGPT-5.1 by 2.828.525.7+2.8
- GPQA DiamondGPT-5.1 by 1.387.386+1.3
- CritPttie4.95.7tie
FactsEven
- AA-Omniscience · Non-hallucinationGPT-5.1 by 25.348.122.8+25.3
- AA-Omniscience · AccuracyGPT-5.1 Codex by 2.237.739.9+2.2
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 Agentic IndexGPT-5.1 Codex by 29.121.650.7+29.1
- Artificial Analysis Coding IndexGPT-5.1 by 12.849.436.6+12.8
- AA-OmniscienceGPT-5.1 by 11.95.4-6.5+11.9
- Terminal-Bench 2.0GPT-5.1 Codex by 5.247.652.8+5.2
- τ²-Bench Telecom (AA run)GPT-5.1 Codex by 1.181.983+1.1
- AA IntelligenceGPT-5.1 by 124.723.7+1
- swe_bench_bashtie6666tie
Questions people ask
Which is better, GPT-5.1 or GPT-5.1 Codex?
GPT-5.1 wins five of the seven areas where both have results: coding, reasoning, images and charts, long documents and following instructions. GPT-5.1 Codex wins agents. They are level on facts.
Which is better for coding?
GPT-5.1. It wins 4 of the 4 coding tests both models report; GPT-5.1 Codex wins none.
Which is cheaper?
GPT-5.1 costs $1.25 per million input tokens and $10.00 per million output tokens; GPT-5.1 Codex costs $1.25 and $10.00. For a million tokens read plus a million written, they cost about the same.
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.