GPT-6 Astra, Claude Fable 5.1, Gemini 3.8 Flash: How the Three Models Compare

Three major AI models — OpenAI's GPT-6 Astra, Anthropic's Claude Fable 5.1, and Google's Gemini 3.8 Flash — launched within the same week in September 2026. On vendor benchmarks, Astra led in areas like math, abstract reasoning, and computer-use tasks, while independent indices from Artificial Analysis ranked Fable 5.1 slightly ahead in both overall capability and coding. All three models share a 1-million-token context window, but pricing diverges sharply: Astra and Fable 5.1 are priced at $10 per million input tokens and $50 per million output tokens, whereas Gemini 3.8 Flash is available at a promotional rate of $0.75 and $3.75 respectively. At a moderate workload of 1,000 daily requests, that gap translates to roughly $80 per day for the premium models versus about $6 for Flash. Analysts suggest the three models serve distinct use cases — Astra for research and science tasks, Fable 5.1 for complex agentic coding, and Gemini Flash for high-volume, cost-sensitive applications.