GPT-5 vs GPT-5.1 Codex
Wins 5 of 7 areas
Coding · Reasoning · Images and charts · Long documents · Following instructions
Wins 2 of 7 areas
Agents · Facts
GPT-5 is the stronger all-rounder.GPT-5.1 Codex is better at facts.
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 software31GPT-53 of 4 tests
- ReasoningHard problems that need careful thinking10GPT-51 of 3 tests · 2 ties
- Images and chartsUnderstanding pictures, charts and video10GPT-51 of 1 test
- Long documentsFinding answers in very long texts10GPT-51 of 1 test
- Following instructionsDoing exactly what it is asked10GPT-51 of 1 test
- FactsGetting facts right instead of making them up01GPT-5.1 Codex1 of 2 tests · 1 tie
- AgentsCarrying out multi-step tasks on its own01GPT-5.1 Codex1 of 1 test
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 three tests each model wins by the widest margin. Scores are out of 100.
Where GPT-5 pulls ahead
- Reasons across sets of long documentsAA-LCR+8.9points ahead
- Follows unfamiliar, precisely checkable instructionsIFBench+3.1points ahead
- Very hard expert questions across many subjectsHumanity's Last Exam+2.8points ahead
Where GPT-5.1 Codex pulls ahead
- Real work tasks from 44 professionsGDPVal+13.6points ahead
- Avoids making up answers it doesn't knowAA-Omniscience · Non-hallucination+5points ahead
- Hard command-line tasks in a real terminalTerminal-Bench Hard+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
- LMArena · WebDevGPT-5 by 82 rating points14181336+82 rating
- SciCodeGPT-5 by 2.742.940.2+2.7
- Terminal-Bench HardGPT-5.1 Codex by 2.232.634.8+2.2
- SWE-bench VerifiedGPT-5 by 1.274.973.7+1.2
ReasoningGPT-5
- Humanity's Last ExamGPT-5 by 2.828.525.7+2.8
- GPQA Diamondtie85.486tie
- CritPttie5.75.7tie
FactsGPT-5.1 Codex
- AA-Omniscience · Non-hallucinationGPT-5.1 Codex by 517.822.8+5
- AA-Omniscience · Accuracytie40.339.9tie
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 24.226.550.7+24.2
- Terminal-Bench 2.0GPT-5.1 Codex by 17.635.252.8+17.6
- AA-OmniscienceGPT-5.1 Codex by 2.2-8.7-6.5+2.2
- τ²-Bench Telecom (AA run)GPT-5 by 1.884.883+1.8
- Artificial Analysis Coding IndexGPT-5 by 1.237.836.6+1.2
- swe_bench_bashGPT-5.1 Codex by 16566+1
- AA Intelligencetie2323.7tie
Questions people ask
Which is better, GPT-5 or GPT-5.1 Codex?
GPT-5 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 and facts.
Which is better for coding?
GPT-5. It wins 3 of the 4 coding tests both models report; GPT-5.1 Codex wins 1.
Which is cheaper?
GPT-5 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.