GPT-6 Astra vs Claude Fable 5.1

GPT-6 Astra in brief

GPT-6 Astra specs and pricing: OpenAI's flagship SI model (September 2026) with a 1.05M-token context window at $10/$50 per million tokens, plus how it compares.

• Long-horizon agentic work and computer use
• Software engineering
• About 1.05M-token context with 128K output
• First model rated "Critical" for cyber capability under OpenAI's framework

Claude Fable 5.1 in brief

Claude Fable 5.1 specs and pricing: Anthropic's most capable model (September 2026), $10/$50 per million tokens, 1M-token context, and how it compares with GPT-6 Astra.

• Anthropic's top tier for hard reasoning
• Long-horizon agentic work
• 1M-token context and 128K output
• Adaptive thinking always on

Which should you choose?

Choose GPT-6 Astra if you need: the hardest multi-step agent tasks; large codebases and complex engineering; research and analysis where quality matters more than cost.

Choose Claude Fable 5.1 if you need: tasks where claude opus 5.5 falls short; complex research and analysis; long-running autonomous coding and agent workflows.

For most teams the best test is your own workload: run the same 20–50 real prompts through both models and compare quality, speed and cost. Benchmarks published by labs use different settings and rarely match everyday use.