Stated negative: identical price, Fable 5.1 leads both independent indices
GPT-6: Astra and Claude Fable 5.1 both list at $10 per 1M input and $50 per 1M output tokens. At that identical price, Claude Fable 5.1 currently scores higher on both Artificial Analysis composites: Intelligence Index 66 against 61, and Coding Agent Index 70 against 67. A page that only cites Astra's wins would not be a comparison page.
Independent index scoreboard
Both figures come from Artificial Analysis, an independent third party, not from either vendor.
| Index | GPT-6: Astra | Claude Fable 5.1 | Delta |
|---|---|---|---|
| Intelligence Index | 61 | 66 | Fable +5 |
| Coding Agent Index | 67 | 70 | Fable +3 |
Price and cache economics
List price is identical, but the two diverge sharply on cached input: Claude Fable 5.1 reads cache at $0.25 per 1M tokens; GPT-6: Astra reads cache at $1.00 per 1M, four times more. On a cache-heavy agent this compounds well beyond the headline price parity.
| Dimension | GPT-6: Astra | Claude Fable 5.1 |
|---|---|---|
| Input $/1M | $10.00 | $10.00 |
| Output $/1M | $50.00 | $50.00 |
| Cached input $/1M | $1.00 | $0.25 |
| Context window | 1,050,000 | 1,000,000 |
| Max output tokens | 128,000 | 128,000 |
| Input modalities | Text, image | Text, image, file |
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Where Astra is ahead on OpenAI's own numbers
On OpenAI's vendor-reported tables, GPT-6: Astra posts strong scores on FrontierMath Tier 4 (v2) at 97.6% and ExploitBench at 100.0%. Anthropic has not published matching runs on those exact evaluations for Claude Fable 5.1, so this is not a head-to-head; it states what OpenAI reported for its own model.
When to pick which
Pick Claude Fable 5.1 when the workload is cache-heavy (the $0.25 read rate compounds fast) or when the independent composite scores matter more than any single vendor benchmark. Pick GPT-6: Astra when you specifically need its 1,050,000-token context ceiling, image input alongside text, or one of the OpenAI-specific evaluations where it scores strongly.