Claude Opus 5.5 Tops Mazur Constrained Story Writing Benchmark

Anthropic's Claude Opus 5.5 ranked first on the Mazur Constrained Story Writing 50-task sample with a mean score of 1.00 at an estimated $0.0242 per task, according to the published leaderboard. OpenAI's GPT-6 Astra and GPT-6.1 Sol Pro tied for second at 0.99, with Sol Pro costing $0.0121 per task, while Anthropic's Claude Sonnet 5.5 placed fourth at 0.98 and $0.0106 per task. The 50 open-ended tasks were graded 0–10 by OpenAI's GPT-5.6 Sol Pro against a fixed rubric and normalized to a 0–1 scale, with reasoning effort pinned to max for every model exposing such a control.

Claude Opus 5.5 Tops Mazur Constrained Story Writing Benchmark Anthropic’s Claude Opus 5.5 scored 1.00 on the 50-task sample at $0.0242 per task. OpenAI’s GPT-6 Astra and GPT-6.1 Sol Pro tied for second at 0.99, with Sol Pro costing $0.0121 per task. By Ryan Merket https://runtimewire.com/author/ryan-merket · Published Leaderboard | Rank | Model | Mean score | Est. cost/task | |---|---|---|---| | 1 | Anthropic: Claude Opus 5.5 https://runtimewire.com/models/anthropic/claude-opus-5.5 | 1.00 | $0.0242 | | 2 | OpenAI: GPT-6 Astra https://runtimewire.com/models/native-openai/gpt-6-astra-576a599a64cb3dde | 0.99 | $0.0599 | | 3 | OpenAI: GPT-6.1 Sol https://runtimewire.com/models/native-openai/gpt-6.1-sol-dedfefd51120f283 Pro | 0.99 | $0.0121 | | 4 | Anthropic: Claude Sonnet 5.5 | 0.98 | $0.0106 | | 5 | Z.ai: GLM 5.3 Prime | 0.97 | $0.0111 | | 6 | xAI: Grok Latest | 0.84 | $0.0077 | | 7 | Google: Gemini 3.8 Flash | 0.70 | $0.0047 | | 8 | Qwen: Qwen3.8 Max Prime | 0.66 | $0.0141 | | 9 | StepFun: Step 3.7 Flash | 0.49 | $0.0014 | How we scored it Every model answered the same 50-task battery from Mazur Constrained Story Writing 50-task sample Lech Mazur — LLM Creative Story-Writing Benchmark; published constrained briefs and archived V4 grading protocol , one task at a time, with no tools and no retries on content. 50 open-ended tasks were graded 0–10 by OpenAI: GPT-5.6 Sol Pro against a fixed rubric — blind to which model wrote the answer — and normalized to the same 0–1 scale. Reasoning effort was pinned to max for every model whose lane exposes a control OpenAI-style reasoning effort , Anthropic extended thinking, Gemini thinking config . Models marked vendor default on the interactive board expose no such control and ran as shipped. A model's mean score averages its graded tasks; a generation failure counts as 0. Cost per task is estimated from each model's published per-token pricing "—" where pricing isn't public , so treat it as directional, not billing-exact. Grading could not be completed for every task on 9 models; their means cover the graded subset. Explore every prompt, answer, and per-task grade in the interactive leaderboard https://runtimewire.com/benchmarks/mazur-writing-leaderboard .