PyyanThe AI Index

Pyyan / Compare / Claude Opus 4.8 vs Claude Fable 5

Claude Opus 4.8 vs Claude Fable 5

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Language Models · verified 13 Aug 2026

Claude Opus 4.8Anthropiccurrent
Claude Fable 5Anthropiccurrent
3 slots left
SpecificationClaude Opus 4.8Claude Fable 5
SummaryPrevious Opus flagship — warmer prose, strong long-horizon work.Most capable widely released model, for the hardest reasoning and long-horizon agentic work.
Context1M1M
Input ($/Mtok)$5$10
Output ($/Mtok)$25$50
LicenceProprietaryProprietary
Max output128K128K
Model IDclaude-opus-4-8claude-fable-5
CategoryLanguage ModelsLanguage Models
OfficialAnthropic ↗Anthropic ↗

Highlighted rows are where these differ.

Claude Opus 4.8

  • Mid-session system messages supported
  • Adaptive thinking only — budget_tokens removed

Best for long-horizon agents.

Full spec sheet →

Claude Fable 5

  • Thinking is always on — the `thinking` param is rejected
  • Raw chain of thought is never returned
  • Requires 30-day data retention; unavailable under ZDR

Best for the hardest problems.

Full spec sheet →