GPT-6 Astra vs Claude Fable 5.1
Both are September 2026 flagships at $10/$50 list and $5/$25 here. Astra is OpenAI computer use and Codex. Fable 5.1 is Anthropic's escalation above Opus 5. Neither is a default for everyday coding.
Input / M (llmrelay): OpenAI and Anthropic list are both $10. Cached input is $1 on Astra and $0.25 on Fable 5.1; we do not currently pass CacheRatio through.
Model id: The Fable id is hyphenated. claude-fable-5.1 returns no channel.
Where OpenAI / Anthropic put it: Astra is not on ChatGPT Free or Go. Fable 5.1 is generally available; Mythos 5.1 is invitation-only.
Prices are llmrelay's, at 50% of official list. Specs are the vendor's own published figures (Anthropic model docs), not our benchmarks. We do not publish scores we cannot source.
Use GPT-6 Astra when
- +You need OpenAI computer use, Codex, or ChatGPT Sites — fill a form, drive a browser, ship a page from a prompt.
- +The 3D-game clips you saw were the model operating Blender or Three.js, not a native 3D endpoint. Reproduce that workflow on the API if you already live in OpenAI tools.
- +You want a second opinion next to Claude on the same key.
Use Claude Fable 5.1 when
- +You are in Claude Code and Opus 5 already failed the specific task. Anthropic still says start on Opus 5.
- +The job is a long-horizon repo change or root-cause review, and you will pay for always-on thinking.
- +You want the current Fable snapshot at the same $5/$25 we charge for Fable 5, with Anthropic's cheaper cache hits on their card.
The honest answer
Same invoice, different door. Astra if the work is OpenAI computer use or Codex; Fable 5.1 if Opus 5 already lost. For everyday coding, Claude Opus 5 at $2.50/$12.50 is the default on this key — switching is one model id.
What this costs you per month
At 50M input and 5M output tokens a month — a realistic heavy agent workload.
Struck-through column is the vendor's list price for the same traffic. Adjust the numbers on the calculator.
One key covers both
Switching between them is a model-id change, not a new account. Prepaid, no subscription, $10 minimum — enough to run the same prompt through both and settle the argument with your own output.
Next steps on this decision
Per-model detail for both sides, and the adjacent comparisons people usually read alongside this one.
- GPT-6 Astra pricing and specs$5.00/M in, $25.00/M out — half list. OpenAI’s current flagship. API, ChatGPT paid plans, half list here.
- Claude Fable 5.1 pricing and specs$5.00/M in, $25.00/M out — half list. Anthropic’s current top Claude. Same $10/$50 list, cheaper cache reads.
- GPT-6 Astra vs Opus 5 — is 2× worth it?Astra is OpenAI's current flagship.
- Cost calculatorPut your own monthly token volume in and see the bill against vendor list price.
- Full price listEvery model we serve, at 50% of official list. No subscription, no volume gate.
- All comparisonsModel-vs-model and gateway-vs-gateway, with sourced specs only.