Hy4 is the stronger all-rounder.GPT-5.5 is better at reasoning.
Scores updated · 17 tests both models report · How we compare
Where each one wins
Tests won in each of the three 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.
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.
Hy4 costs 90% 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 Hy4 pulls ahead
- Multi-step tasks using many real software toolsMCP Atlas+8.4points ahead
- Long, multi-file coding tasks in real codebasesSWE-bench Pro+7.1points ahead
- Command-line tasks in a real terminalTerminal-Bench 2.1+1.1points ahead
Where GPT-5.5 pulls ahead
- Research-level physics problemsCritPt+10.2points ahead
- Graduate-level biology, physics and chemistry questionsGPQA Diamond+1.2points ahead
Every test, side by side
All 17 tests both models report. The winning score is in its model's colour; marks a score checked independently.
CodingHy4
- LMArena · WebDevHy4 by 144 rating points14871631+144 rating
- SWE-bench ProHy4 by 7.158.665.7+7.1
- Terminal-Bench 2.1Hy4 by 1.184.385.4+1.1
ReasoningGPT-5.5
- CritPtGPT-5.5 by 10.227.116.9+10.2
- GPQA DiamondGPT-5.5 by 1.293.592.3+1.2
Other results10 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.
- Program BenchGPT-5.5 by 53.370.817.5+53.3
- JobBenchHy4 by 23.438.361.7+23.4
- SWE-MarathonHy4 by 19.91231.9+19.9
- ToolathlonHy4 by 18.555.674.1+18.5
- OfficeQA ProHy4 by 12.154.166.2+12.1
- NL2RepoHy4 by 8.250.758.9+8.2
- PostTrainBenchHy4 by 7.228.435.6+7.2
- DeepSWEGPT-5.5 by 5.77064.3+5.7
- Agents' Last ExamGPT-5.5 by 3.826.622.8+3.8
- CyberGymGPT-5.5 by 3.481.878.4+3.4
Questions people ask
Which is better, GPT-5.5 or Hy4?
Hy4 wins two of the three areas where both have results: coding and agents. GPT-5.5 wins reasoning.
Which is better for coding?
Hy4. It wins 3 of the 3 coding tests both models report; GPT-5.5 wins none.
Which is cheaper?
GPT-5.5 costs $5.00 per million input tokens and $30.00 per million output tokens; Hy4 costs $0.83 and $2.50. That makes Hy4 about 90% cheaper for the same work.
How do you compare the two?
We use the 17 benchmark tests both models have published scores on. The verdict counts the 7 tests in the eight capability areas, and a gap under one point (ten on rating-style scales) counts as a tie. The other 10 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.