Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) vs Claude Sonnet 4.5
Wins 5 of 6 areas
Coding · Agents · Reasoning · Images and charts · Long documents
Wins 0 of 6 areas
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Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) is the stronger all-rounder.Claude Sonnet 4.5 is cheaper.
Scores updated · 11 tests both models report · How we compare
Where each one wins
Tests won in each of the six 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.
- AgentsCarrying out multi-step tasks on its own20Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)2 of 2 tests
- ReasoningHard problems that need careful thinking20Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)2 of 2 tests
- CodingWriting and fixing software10Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)1 of 1 test
- Images and chartsUnderstanding pictures, charts and video10Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)1 of 1 test
- Long documentsFinding answers in very long texts10Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)1 of 1 test
- FactsGetting facts right instead of making them up11Even1 each
Coding, images and charts and long documents 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.
Claude Sonnet 4.5 costs 25% 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 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) pulls ahead
- Very hard expert questions across many subjectsHumanity's Last Exam+36.9points ahead
- Real work tasks from 44 professionsGDPVal+33.8points ahead
- Answers hard knowledge questions correctlyAA-Omniscience · Accuracy+31.7points ahead
Where Claude Sonnet 4.5 pulls ahead
- Avoids making up answers it doesn't knowAA-Omniscience · Non-hallucination+19.3points ahead
Every test, side by side
All 11 tests both models report. The winning score is in its model's colour; marks a score checked independently.
CodingClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)
- SciCodeClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 13.659.345.7+13.6
AgentsClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)
- Terminal-Bench 4.0Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 52.552.50+52.5
- GDPValClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 33.854.320.5+33.8
ReasoningClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)
- Humanity's Last ExamClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 36.954.717.8+36.9
- CritPtClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 26.627.71.1+26.6
FactsEven
- AA-Omniscience · AccuracyClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 31.764.532.9+31.7
- AA-Omniscience · Non-hallucinationClaude Sonnet 4.5 by 19.331.650.9+19.3
Images and chartsClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)
- MMMU-ProClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 1785.768.7+17
Long documentsClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback)
- AA-LCRClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 1284.372.3+12
Other results2 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 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 40.440.3-0.1+40.4
- AA IntelligenceClaude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) by 30.551.220.7+30.5
Questions people ask
Which is better, Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) or Claude Sonnet 4.5?
Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) wins five of the six areas where both have results: coding, agents, reasoning, images and charts and long documents. Claude Sonnet 4.5 wins none, but costs 25% less. They are level on facts.
Which is better for coding?
Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback). It wins the one coding test both models report.
Which is cheaper?
Claude Opus 5.5 (Adaptive Reasoning, Medium Effort, Default Fallback) costs $4.00 per million input tokens and $20.00 per million output tokens; Claude Sonnet 4.5 costs $3.00 and $15.00. That makes Claude Sonnet 4.5 about 25% cheaper for the same work.
How do you compare the two?
We use the 11 benchmark tests both models have published scores on. The verdict counts the 9 tests in the eight capability areas, and a gap under one point (ten on rating-style scales) counts as a tie. The other 2 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.