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Three.dev study: Sonnet 5 bill rose 4% despite 33% list price cut

·2026.10.21 06:08

Key point

Token inflation and longer outputs offset the price reduction, resulting in higher actual costs for Sonnet 5 compared to Sonnet 4.6.

Details

  • Sonnet 5 bills were 4% higher than Sonnet 4.6 despite a 33% drop in list price, driven by increased token counts and output length.
  • Input tokens grew 1.37x and output tokens grew 1.66x on Sonnet 5, with a single sentence summary increasing from 48 to 90 billed tokens.
  • Sonnet 5.5 increased bills by 7% overall and 50% on fact questions due to default reasoning, while reducing JSON extraction costs by 12%.
  • Opus 4.7 bills were 47% higher than Opus 4.6, with 40% more input tokens and 51% more output tokens for the same text.
  • The study used 191 requests from the "Attention Is All You Need" paper, including summaries, explanations, fact questions, JSON extractions, and translations.
  • Tests were conducted on public APIs at list price on 7 and 8 October 2026, with no caching, batch processing, or tools enabled.
tokenizationanthropicpricingclaude-opusclaude-sonnetcost-analysisapi-benchmark
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