GPT-6 or Fable 5.1: Which Is Better in 2026?

GPT-6 Astra vs Claude Fable 5.1: same $10/$50 headline price, but cache reads, long-prompt surcharges and context limits decide the real cost. Full 2026 specification, pricing and capability comparison.

Two frontier models now sit at the very top of the market, and they cost exactly the same on paper.

OpenAI's GPT-6 Astra and Anthropic's Claude Fable 5.1 both list at $10 per million input tokens and $50 per million output tokens, both offer a roughly one-million-token context window, and both cap output at 128K tokens.

So the question is not which one is cheaper on the headline rate.

It is which one is cheaper for the way you actually use it , and which one is stronger on the work you actually do.

This comparison uses the published specifications from both vendors, plus the scores in our live AI model comparison tool .

The short answer Long-running agents that re-read the same context: Claude Fable 5.1.

Cache reads are $0.25 per million tokens against Astra's $1, and Anthropic estimates 25% lower typical costs and up to ~45% on heavily agentic work.

Very large single prompts (above 272K tokens): Claude Fable 5.1.

Astra charges 2× input and cache rates and 1.5× output for the entire request once a prompt crosses 272K input tokens; Anthropic charges its normal per-token rate across the full window.

Mixed reasoning, multimodal work and the broadest ecosystem: GPT-6 Astra.

It carries the stronger multimodal profile and slots into the wider OpenAI tooling most teams already run.

Most production traffic: neither.