{
  "description": "The Unbiased Verbosity Index: output tokens per identical task, measured across models. Index = geometric mean of each model's output tokens relative to the per-task median across all measured models. 1.00 = median verbosity. Higher = more tokens billed for the same work.",
  "edition": 1,
  "measured": "2026-07-30",
  "method": "6 task types (code generation, JSON extraction, summarization, quantitative analysis, email drafting, short factual answer) x 2 runs per model, identical prompts, no length guidance, default settings. Prompts published at unbiased.ai/blog/verbosity-index/.",
  "index": {
    "claude-opus-5": 1.48,
    "claude-fable-5": 1.14,
    "claude-sonnet-5": 1.13,
    "claude-opus-4-8": 0.92,
    "pareto": 0.75,
    "claude-haiku-4-5": 0.61
  },
  "mean_output_tokens": {
    "codegen": {
      "claude-fable-5": 3142,
      "claude-opus-5": 5305,
      "claude-opus-4-8": 2772,
      "claude-sonnet-5": 4032,
      "claude-haiku-4-5": 3247,
      "pareto": 2876
    },
    "extraction": {
      "claude-fable-5": 362,
      "claude-opus-5": 319,
      "claude-opus-4-8": 319,
      "claude-sonnet-5": 319,
      "claude-haiku-4-5": 297,
      "pareto": 259
    },
    "summarize": {
      "claude-fable-5": 225,
      "claude-opus-5": 226,
      "claude-opus-4-8": 194,
      "claude-sonnet-5": 209,
      "claude-haiku-4-5": 126,
      "pareto": 113
    },
    "analysis": {
      "claude-fable-5": 700,
      "claude-opus-5": 998,
      "claude-opus-4-8": 526,
      "claude-sonnet-5": 970,
      "claude-haiku-4-5": 361,
      "pareto": 632
    },
    "email": {
      "claude-fable-5": 710,
      "claude-opus-5": 782,
      "claude-opus-4-8": 474,
      "claude-sonnet-5": 508,
      "claude-haiku-4-5": 311,
      "pareto": 330
    },
    "short_answer": {
      "claude-fable-5": 136,
      "claude-opus-5": 273,
      "claude-opus-4-8": 108,
      "claude-sonnet-5": 125,
      "claude-haiku-4-5": 31,
      "pareto": 81
    }
  },
  "six_task_battery_bill_usd": {
    "claude-fable-5": 0.2722,
    "claude-opus-5": 0.2018,
    "claude-opus-4-8": 0.114,
    "claude-sonnet-5": 0.0633,
    "claude-haiku-4-5": 0.0225,
    "pareto": "at cost"
  }
}