Claude Opus 5.5 vs Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback)
Wins 3 of 5 areas
Coding · Reasoning · Long documents
Wins 0 of 5 areas
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Claude Opus 5.5 is the stronger all-rounder.Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) is cheaper.
Scores updated · 10 tests both models report · How we compare
Where each one wins
Tests won in each of the five 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.
- ReasoningHard problems that need careful thinking10Claude Opus 5.51 of 2 tests · 1 tie
- CodingWriting and fixing software10Claude Opus 5.51 of 1 test
- Long documentsFinding answers in very long texts10Claude Opus 5.51 of 1 test
- AgentsCarrying out multi-step tasks on its own11Even1 each
- FactsGetting facts right instead of making them up11Even1 each
Coding 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 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) costs 50% 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 pulls ahead
- Answers hard knowledge questions correctlyAA-Omniscience · Accuracy+12.2points ahead
- Very hard expert questions across many subjectsHumanity's Last Exam+6.4points ahead
- Code for real scientific research problemsSciCode+5.9points ahead
Where Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) pulls ahead
- Avoids making up answers it doesn't knowAA-Omniscience · Non-hallucination+11.6points ahead
- Complex command-line tasks across many fieldsTerminal-Bench 4.0+4points ahead
Every test, side by side
All 10 tests both models report. The winning score is in its model's colour; marks a score checked independently.
AgentsEven
- Terminal-Bench 4.0Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) by 459.663.6+4
- GDPValClaude Opus 5.5 by 1.368.367+1.3
ReasoningClaude Opus 5.5
- Humanity's Last ExamClaude Opus 5.5 by 6.461.455+6.4
- CritPttie31.731.4tie
FactsEven
- AA-Omniscience · AccuracyClaude Opus 5.5 by 12.266.254+12.2
- AA-Omniscience · Non-hallucinationClaude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) by 11.641.453+11.6
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 by 14.146.432.3+14.1
- AA IntelligenceClaude Opus 5.5 by 1.657.656+1.6
Questions people ask
Which is better, Claude Opus 5.5 or Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback)?
Claude Opus 5.5 wins three of the five areas where both have results: coding, reasoning and long documents. Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) wins none, but costs 50% less. They are level on agents and facts.
Which is better for coding?
Claude Opus 5.5. It wins the one coding test both models report.
Which is cheaper?
Claude Opus 5.5 costs $4.00 per million input tokens and $20.00 per million output tokens; Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) costs $2.00 and $10.00. That makes Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback) about 50% cheaper for the same work.
How do you compare the two?
We use the 10 benchmark tests both models have published scores on. The verdict counts the 8 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.