GPT-6 Astra vs Claude Fable 5.1: tied on paper, split in practice
GPT-6 Astra and Claude Fable 5.1 score almost the same overall and cost the same. Astra wins math and knowledge; Fable wins the tests people vote on.
GPT-6 Astra is the model we would pick for hard math, science and research questions. Claude Fable 5.1 is the one we would put in front of people. Overall they are close: Astra scores 64.6 on the Noometry Index and Fable scores 62.5, too near for the overall score to pick a winner. Both list at $10 per million input tokens and $50 per million output tokens, so price won't break the tie either.
The useful answer is in the categories, where the two models are not tied at all.
Astra's lead is math, reasoning and knowledge
Astra is first in three categories on Noometry: math (91.9 against Fable's 87.2), reasoning (78.1 against 70.6) and knowledge (66.2 against 55.8). The gaps show up on the hardest tests we track. On FrontierMath Tier 4, Epoch AI's research-level set, Astra scores 97.6% to Fable's 87.8%. On Humanity's Last Exam it reaches 54.8% to 46.5%, and on SimpleQA Verified, a short-answer factual accuracy test, 75.6% to 70.8%.
If your work is analysis, research or anything where a wrong fact costs you, that pattern matters more than the overall score.
Fable wins where people vote
Fable is second in writing and second in multilingual, while Astra sits 49th in writing. Blind human votes drive both categories. On the LMArena text leaderboard Fable is rated 1511 and Astra 1443. That is a large gap for two models this close on everything else, and it matches what the category scores say: Fable 68.7 in writing to Astra's 63.0, and 59.4 to 53.9 in languages other than English.
For chat products, support, drafting and anything customer-facing, Fable is the safer default.
Coding is a coin flip with a pattern
The coding category is a dead heat, 67.8 for Astra and 67.7 for Fable. The individual benchmarks split in an informative way:
| Benchmark | GPT-6 Astra | Claude Fable 5.1 |
|---|---|---|
| FrontierSWE | 65.5% | 56.3% |
| MirrorCode | 46.7% | 73.3% |
| LMArena coding (votes) | 1488 | 1523 |
Astra does better on long, autonomous software-engineering tasks. Fable does better when people judge the output. Teams running unattended coding agents should start with Astra; teams using a model as a pair programmer should start with Fable. Either way, run both on a slice of your own repository before committing.
The price is the same, the cache is not
List prices match, but cached input does not: Fable charges $0.25 per million cached tokens and Astra charges $1. Agent loops that resend the same long context on every step spend most of their tokens on cache reads, so for those workloads Fable costs noticeably less per task.
If neither lead matters to you, Claude Opus 5 is worth a look. It scores 61.2, close behind both, at $5 input and $25 output per million tokens, half the price of either.
Who should pick which
- Pick GPT-6 Astra for math, science, research assistants and long autonomous coding runs.
- Pick Claude Fable 5.1 for writing, chat, support, non-English users and agent loops that lean on prompt caching.
- Pick Claude Opus 5 if you want most of either model at half the price.
The full side-by-side, benchmark by benchmark, is on the GPT-6 Astra vs Claude Fable 5.1 comparison page. Both models have 48 tracked results; see the GPT-6 Astra and Claude Fable 5.1 profiles, or estimate your bill with the cost calculator.
Frequently asked questions
Is GPT-6 Astra better than Claude Fable 5.1?
Not overall: they are close, 64.6 to 62.5 on the Noometry Index. Astra is clearly stronger at math, reasoning and knowledge; Fable is clearly stronger at writing and multilingual work.
Which is cheaper, GPT-6 Astra or Claude Fable 5.1?
They cost the same at list price, $10 input and $50 output per million tokens. Fable's cached input is cheaper at $0.25 against Astra's $1.
Which is better for coding?
Neither overall (67.8 against 67.7). Astra leads on autonomous engineering tasks such as FrontierSWE; Fable leads when people rate the code.
Which has the bigger context window?
Astra, slightly: 1.05M tokens against Fable's 1M.