Claude Fable 5.1 vs GPT-6 Astra: the two new flagships, head-to-head on price
Sticker price is a wash - $10/$50 on both sides, so a live 100K+10K call costs $1.50 on either. Fable 5.1 wins hard the moment you use prompt caching, with $0.25/M cached input against Astra's $1.00/M. Pick Astra only if you're on OpenAI's stack or need the extra 50K context.
Identical sticker prices on both tiers - the cache discount is the only real cost lever.
Claude Fable 5.1 and GPT-6 Astra are the brand new flagship reasoning models from Anthropic and OpenAI, both launched within days of each other in late summer 2026. On sticker price they're identical: $10 per million input tokens and $50 per million output tokens. The real cost difference hides in the caching discount, where Fable 5.1 offers a much deeper cut.
By TechCompare · Updated
Cost Comparison
Based on 100,000 input tokens (50% cached), 5,000 output tokens, and 100 requests.Prices are fetched live from OpenRouter and may include temporary promotional discounts not accounted for in our article and comparison figures.
Side-by-side specs
| Spec | Claude Fable 5.1 | GPT-6 Astra |
|---|---|---|
| Input Cost (per M) | $10.00 | $10.00 |
| Output Cost (per M) | $50.00 | $50.00 |
| Cached Input (per M) | $0.25 (better on this spec) | $1.00 |
| Batch Discount | 50% | 50% |
| Context Window | 1M | 1.05M (better on this spec) |
How they differ
Claude Fable 5.1 is priced at $10.00 per million input tokens and $50.00 per million output tokens, the same base rate as Fable 5, but with a deeper 97.5% caching discount that drops cached input to $0.25 per million (down from Fable 5's 90% / $1.00). GPT-6 Astra is also priced at $10.00/$50.00 but keeps a more standard 90% caching discount ($1.00 per million cached). Both offer a 50% batch discount ($5/$25). Fable 5.1 has a 1M context window, Astra a slightly larger 1.05M. For a representative 100K input + 10K output request, both cost $1.50 live, so the per-call cost ties. The gap only opens on cache-hit-heavy workloads: at high cache rates Fable 5.1's input is four times cheaper.
Verdict
Three of five rows tie: $10.00/M input, $50.00/M output, and 50% batch ($5/M input, $25/M output). The context row is a narrow Astra win at 1.05M tokens against Fable 5.1's 1M. The main cost lever is cached input, where Fable 5.1's 97.5% discount lands at $0.25/M against Astra's 90% discount at $1.00/M - a 4x gap that dominates on agentic loops with stable system prompts. A million cached-input tokens a day on Fable costs $0.25 versus $1.00 on Astra, roughly $270 a year, but multiplied across a heavy agentic pipeline the cache row dwarfs everything else. Choose Astra only when its 1.05M context or OpenAI tooling fit outweighs the cache penalty.
Which should you pick?
Choose Claude Fable 5.1
Agentic loops and long-running automations with stable, heavily-reused prompts. Fable 5.1's 97.5% cache discount makes repetitive-context workloads dramatically cheaper at scale.
Choose GPT-6 Astra
One-shot or low-reuse calls where caching never kicks in, workloads that need the extra 50K tokens of context, or pipelines already wired into OpenAI's tooling. On a pure live call the two models cost exactly the same.