GPT-6 Astra vs Claude Fable 5.1
These two shipped two days apart and landed on the identical headline rate: $10 per million input tokens and $50 per million output. That symmetry makes the list price useless as a tiebreaker and pushes the decision into the parts of the bill nobody quotes. Anthropic cut Fable 5.1 cache reads 75 percent to $0.25 per million on September 1, so a workload that reuses a large system prompt pays roughly 25 percent less than it did on Fable 5, and up to 45 percent less on heavily agentic patterns. OpenAI prices Astra cached input at $1, four times Anthropic's cache read, and adds a second wrinkle Anthropic does not have: prompts above 272,000 input tokens bill at 2x input and cache rates and 1.5x output, which turns the advertised 1,050,000 token window into two pricing regimes. Fable 5.1 has a flat 1 million token window with no long-context surcharge. Both offer 128K max output. On the published numbers Astra is ahead where OpenAI chose to measure: GPQA Diamond 96.0 against 92.6, FrontierMath Tier 4 at 97.6, MRCR v2 at 100 percent in the 256K to 512K band, and SRE-Bench first-attempt resolution at 88.0. Fable 5.1 publishes SWE-bench Pro at 81.2, a row Astra skipped entirely, so the software engineering comparison has no shared benchmark at all. Every figure on both sides is vendor-reported.
Head-to-Head Specs
| Spec | GPT-6 Astra | Claude Fable 5.1 |
|---|---|---|
| Provider | OpenAI | Anthropic |
| Input Price | $10.00/1M | $10.00/1M |
| Output Price | $50.00/1M | $50.00/1M |
| Context Window | 1M | 1M |
| Released | 2026-09 | 2026-09 |
| Capabilities | text, vision, tool-use, code, reasoning | text, vision, tool-use, code, reasoning |
Benchmark Scores
| Benchmark | GPT-6 Astra | Claude Fable 5.1 | Winner |
|---|
See the full benchmark leaderboard for all models.
Category Breakdown
Both are $10 per 1M input and $50 output, identical to the cent
Fable 5.1 cache reads are $0.25 per 1M against $1 for Astra cached input, a 4x gap on the line item that dominates agentic loops
Fable 5.1 bills 1M tokens at one flat rate; Astra doubles input and cache rates and adds 1.5x output above 272K
1,050,000 tokens against 1,000,000, though the last 778K of Astra bills at a premium
OpenAI reports MRCR v2 8-needle at 100 percent from 256K to 512K and 96.3 from 512K to 1M; Anthropic published no comparable row
GPQA Diamond 96.0 against 92.6, both vendor-reported
Anthropic reports SWE-bench Pro at 81.2 and OpenAI published no SWE-bench Pro figure for Astra, so there is nothing to compare
Fable 5.1 was broadly available on day one; Astra started as a limited partner preview and reached paid users in a restricted build that refuses some cybersecurity prompts
Choose GPT-6 Astra when:
- ▸Long context retrieval where MRCR-style recall past 256K is the failure mode
- ▸Incident response and operational triage work
- ▸Frontier mathematics and graduate science reasoning
- ▸Prompts that stay comfortably under the 272K billing cliff
Choose Claude Fable 5.1 when:
- ▸Agentic loops that reuse a large cached prompt on every step
- ▸Long context work that needs flat pricing across the full window
- ▸Software engineering tasks where SWE-bench Pro is the closest proxy
- ▸Teams that need broad availability now without preview gating
Frequently Asked Questions
Which is better, GPT-6 Astra or Claude Fable 5.1?
It depends on your use case. GPT-6 Astra from OpenAI excels at long context retrieval where mrcr-style recall past 256k is the failure mode, while Claude Fable 5.1 from Anthropic is better for agentic loops that reuse a large cached prompt on every step. See the full comparison above for detailed benchmarks and pricing.
How much does GPT-6 Astra cost compared to Claude Fable 5.1?
GPT-6 Astra costs $10.00 input and $50.00 output per 1M tokens. Claude Fable 5.1 costs $10.00 input and $50.00 output per 1M tokens.
What is the context window difference between GPT-6 Astra and Claude Fable 5.1?
GPT-6 Astra supports 1M tokens, while Claude Fable 5.1 supports 1M tokens.