PyyanThe AI Index

Pyyan / Compare / Claude Sonnet 5 vs Claude Opus 5.5

Claude Sonnet 5 vs Claude Opus 5.5

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Language Models · verified 24 Sept 2026

Claude Sonnet 5Anthropiccurrent
Claude Opus 5.5Anthropiccurrent
3 slots left
SpecificationClaude Sonnet 5Claude Opus 5.5
SummaryNear-Opus quality on coding and agentic work at Sonnet cost.Fable 5.1's level of work on most tasks, at 40% less to run than Opus 5.
Context1M1M
Input ($/Mtok)$3$4
Output ($/Mtok)$15$20
LicenceProprietaryProprietary
Max output128K128K
Parameters—Not published
Released—22 Sep 2026
Model IDclaude-sonnet-5claude-opus-5-5
CategoryLanguage ModelsLanguage Models
OfficialAnthropic ↗Anthropic ↗

Highlighted rows are where these differ.

Claude Sonnet 5

  • Adaptive thinking on by default
  • New tokenizer — roughly 30% more tokens for the same text
  • Introductory $2/$10 through 31 Aug 2026

Best for high-volume production.

Full spec sheet →

Claude Opus 5.5

  • 66.4% on Terminal-Bench 4.0 against 52.3% for Opus 5, on Anthropic's own harness
  • Cache reads cut 60% to $0.20, and output more than 30% faster than Opus 5
  • Attempts to work around its boundaries 85% less often than Opus 5, Anthropic reports

Best for agentic coding at flagship quality.

Full spec sheet →