GPT-5.5 vs GPT-6 Luna
Wins 7 of 8 areas
Coding · Reasoning · Facts · Images and charts · Math · Long documents · Following instructions
Wins 0 of 8 areas
—
GPT-5.5 is the stronger all-rounder.GPT-6 Luna is cheaper.
Scores updated · 35 tests both models report · How we compare
Where each one wins
Tests won in each of the eight areas we test. Each piece is one test, so a longer bar means more evidence; grey means the two scored within a point of each other.
- ReasoningHard problems that need careful thinking40GPT-5.54 of 5 tests · 1 tie
- MathCompetition and research-level math30GPT-5.53 of 3 tests
- CodingWriting and fixing software31GPT-5.53 of 4 tests
- FactsGetting facts right instead of making them up21GPT-5.52 of 3 tests
- Images and chartsUnderstanding pictures, charts and video10GPT-5.51 of 2 tests · 1 tie
- Long documentsFinding answers in very long texts10GPT-5.51 of 1 test
- Following instructionsDoing exactly what it is asked10GPT-5.51 of 1 test
- AgentsCarrying out multi-step tasks on its own11Even1 each
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-6 Luna costs 98% 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 GPT-5.5 pulls ahead
- Abstract visual puzzles that people can solveARC-AGI-2+25.7points ahead
- Short factual questions, answered correctlySimpleQA Verified+21.6points ahead
- Extremely hard research-level math problemsFrontierMath Tier 4+16.4points ahead
Where GPT-6 Luna pulls ahead
- Avoids making up answers it doesn't knowAA-Omniscience · Non-hallucination+12.3points ahead
- Real work tasks from 44 professionsGDPVal+4.1points ahead
Every test, side by side
All 35 tests both models report. The winning score is in its model's colour; marks a score checked independently.
CodingGPT-5.5
- LMArena · WebDevGPT-6 Luna by 90 rating points14871577+90 rating
- LiveBench · CodingGPT-5.5 by 3.282.279+3.2
- LiveBench · Agentic CodingGPT-5.5 by 2.85451.2+2.8
- SciCodeGPT-5.5 by 1.255.854.6+1.2
AgentsEven
- GDPValGPT-6 Luna by 4.142.546.6+4.1
- Terminal-Bench 4.0GPT-5.5 by 214.612.6+2
ReasoningGPT-5.5
- ARC-AGI-2GPT-5.5 by 25.78559.3+25.7
- LiveBench · ReasoningGPT-5.5 by 7.989.781.8+7.9
- CritPtGPT-5.5 by 7.727.119.4+7.7
- Humanity's Last ExamGPT-5.5 by 7.345.838.5+7.3
- ARC-AGI-3tie0.40.1tie
FactsGPT-5.5
- SimpleQA VerifiedGPT-5.5 by 21.66341.4+21.6
- AA-Omniscience · AccuracyGPT-5.5 by 14.25843.8+14.2
- AA-Omniscience · Non-hallucinationGPT-6 Luna by 12.31123.3+12.3
Images and chartsGPT-5.5
- LMArena · VisionGPT-5.5 by 84 rating points12951211+84 rating
- MMMU-Protie79.979.7tie
MathGPT-5.5
- FrontierMath Tier 4GPT-5.5 by 16.472.556.1+16.4
- LiveBench · MathematicsGPT-5.5 by 6.895.989.1+6.8
- FrontierMath Tiers 1-3 (v2)GPT-5.5 by 6.385.379+6.3
Following instructionsGPT-5.5
- LiveBench · Instruction FollowingGPT-5.5 by 14.870.755.9+14.8
Other results14 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.
- Agents' Last ExamGPT-6 Luna by 24.326.650.9+24.3
- AA-OmniscienceGPT-5.5 by 19.820.50.7+19.8
- livebench_languageGPT-5.5 by 13.687.473.8+13.6
- HealthBench ProfessionalGPT-6 Luna by 10.151.861.9+10.1
- HealthBench Professional length-adjustedGPT-6 Luna by 951.860.8+9
- ARC-AGI-1GPT-5.5 by 8.39586.7+8.3
- livebench_data_analysisGPT-5.5 by 8.281.673.4+8.2
- GDP (Surge AI)GPT-5.5 by 2.124.922.8+2.1
- HealthBench length-adjustedGPT-5.5 by 256.554.5+2
- HealthBenchGPT-5.5 by 1.956.554.6+1.9
- DeepSWE 1.1tie6766.6tie
- AA Intelligencetie38.438.1tie
- HealthBench Consensus length-adjustedtie95.695.9tie
- HealthBench Hard length-adjustedtie31.531.4tie
Questions people ask
Which is better, GPT-5.5 or GPT-6 Luna?
GPT-5.5 wins seven of the eight areas we test: coding, reasoning, facts, images and charts, math, long documents and following instructions. GPT-6 Luna wins none, but costs 98% less. They are level on agents.
Which is better for coding?
GPT-5.5. It wins 3 of the 4 coding tests both models report; GPT-6 Luna wins 1.
Which is cheaper?
GPT-5.5 costs $5.00 per million input tokens and $30.00 per million output tokens; GPT-6 Luna costs $0.10 and $0.50. That makes GPT-6 Luna about 98% cheaper for the same work.
How do you compare the two?
We use the 35 benchmark tests both models have published scores on. The verdict counts the 21 tests in the eight capability areas, and a gap under one point (ten on rating-style scales) counts as a tie. The other 14 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.