Model comparison
Claude Fable 5.1 vs GPT-6 Astra
Anthropic against OpenAI, compared on context, price, and verified benchmark results.
Catalog record checked September 5, 2026Individual provider fields may changeEvidence confidence: High — see receipts below
Anthropic
Claude Fable 5.1
Frontier
OpenAI
GPT-6 Astra
Frontier
| Specification | Claude Fable 5.1 | GPT-6 Astra |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Tier | Frontier | Frontier |
| Context window | 1M | Winner: 1.05M |
| Max output | 128K | 128K |
| Input / 1M tokens | $10 | $10 |
| Output / 1M tokens | $50 | $50 |
| Weights | Closed | Closed |
| Parameters | Not disclosedUnverified | computer-use flagship |
| Reasoning levels | adaptive | low, medium, high, xhigh, max |
| Modalities | text, image | text, image |
| API model id | claude-fable-5-1 | gpt-6-astra |
| Released | September 1, 2026 | September 3, 2026 |
| Artificial Analysis Intelligence Index (2026-08-14) | 66 | Not verifiedUnverified |
| Artificial Analysis Intelligence Index [max] (2026-09-03) | Not verifiedUnverified | 61.2 |
| Humanity's Last Exam (2026-09-01) | Winner: 65 | 57.2 |
| Terminal-Bench 2.1 (2026-09-05) | Winner: 91.4 | 89.9 |
| DeepSWE 1.1 (2026-09-03) | 67.4 | Winner: 74.1 |
| OSWorld 2.0 (offline) (2026-09-03) | Not verifiedUnverified | 72.6 |
| GPQA Diamond (2026-09-03) | Not verifiedUnverified | 96 |
Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.
Benchmark receipts
- 2026-09-05: Artificial Analysis Terminal-Bench v2.1 (independent, Terminus 2 harness — conflicts with tbench.ai 87.4; harness difference preserved)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
- 2026-09-03: Terminal-Bench official leaderboard (independent, native harness, high effort; captured 2026-09-03 — the live board has since moved to Terminal-Bench 4.0)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
- 2026-09-03: OpenAI GPT-6 Astra launch chart (vendor, with tools; transcribed by Vellum)Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task. Comparability: directly comparable
- 2026-09-03: OpenAI GPT-6 Astra launch chart (independent cross-vendor; Fable 5.1 not on the official Datacurve leaderboard)Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task. Comparability: directly comparable
- 2026-09-03: Artificial AnalysisComposite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).
- 2026-09-01: Anthropic announcement comparison table (vendor, with tools; 60.9 no tools)Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise. Comparability: comparable with caveat — Subset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.
Pricing tiers: Claude Fable 5.1: Priced with Fable 5 at $10/$50 per MTok; cache reads cut 75% to $0.25/MTok. Adaptive thinking always on (default effort high); knowledge cutoff Jun 2026. Sibling Mythos 5.1 launched the same day. · GPT-6 Astra: Standard $10/$50 per MTok (≤272K context); >272K input billed $20/$75 (Fast mode output $100). Cached input $1/MTok; Fast mode is 2x price for ~2.5x speed. Knowledge cutoff Apr 30 2026. Rolling out over several days from 2026-09-03; Enterprise tenants get it disabled by default.
Claude Fable 5.1
Claude Fable 5.1 is Anthropic's September 2026 flagship refresh, debuting at the top of LiveBench and the Artificial Analysis Intelligence Index.
Best for
- Frontier agents
- Hardest reasoning work
- Fable 5 workloads at the same price
Watch out
Early-life model: leaderboard position is from launch-week boards; recheck before committing spend.
GPT-6 Astra
GPT-6 Astra is OpenAI's computer-use flagship — the first model it gates at the Preparedness Framework's 'Critical' cybersecurity threshold, trained on >100,000 GPUs at Stargate.
Best for
- Computer-use agents
- Agentic coding
- Hard reasoning
Watch out
Gated at the 'Critical' cyber threshold and disabled by default for Enterprise; long-context work bills $20/$75 above 272K input tokens.
When the cheaper one wins
Both charge $50 per million output tokens at standard rates, so output price is not the split. Prefer the row whose “best for” line matches the job, then confirm the live vendor rate.
Run the model pickerEvidence confidence: High
How strong and complete the evidence behind this comparison is — not a prediction of which model is better.
- Pricing verified on both sides — Input and output rates are verified for both models.
- 4/5 core specs verified on both sides — Not published for at least one side: parameter count.
- 4 shared named benchmarks with differing scores — Measured on: Artificial Analysis Intelligence Index, Humanity's Last Exam, Terminal-Bench 2.1, DeepSWE 1.1.
- Verified within the last 90 days — Newest catalog check was 6 days ago.
- Both models carry source citations — Each side has at least two catalog sources on record.
Source receipts
Each catalog figure was checked against the provider or an independent second source on the date shown.
- Claude Fable 5.1: Anthropic pricing — Fable 5.1/Mythos 5.1 $10/$50 (accessed 2026-09-03)
- Claude Fable 5.1: Anthropic models overview — Fable 5.1 (1M context, 128K output) (accessed 2026-09-03)
- Claude Fable 5.1: Artificial Analysis — Fable 5.1 Intelligence Index 66 #1 (accessed 2026-09-01)
- GPT-6 Astra: OpenAI — Introducing GPT-6 Astra (accessed 2026-09-03)
- GPT-6 Astra: OpenAI API pricing (gpt-6-astra $10/$50) (accessed 2026-09-03)
- GPT-6 Astra: CNBC — OpenAI launches GPT-6 Astra (accessed 2026-09-03)
- GPT-6 Astra: OpenAI model docs — gpt-6-astra (128K max output, effort levels) (accessed 2026-09-05)
Related comparisons
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- Claude Fable 5.1 vs Claude Sonnet 5
- Claude Fable 5.1 vs DeepSeek V4 Pro
- Claude Fable 5.1 vs Gemini 3.1 Pro
Diving deeper on one model? Claude Fable 5.1 · GPT-6 Astra
Common questions
Claude Fable 5.1 vs GPT-6 Astra
Answered from the verified figures on this page rather than general guidance.
Is Claude Fable 5.1 or GPT-6 Astra cheaper for input?
Both cost $10 per million input tokens at standard rates, so input price is not a deciding factor between them.
Is Claude Fable 5.1 or GPT-6 Astra cheaper for output?
Both cost $50 per million output tokens at standard rates, so output price is not a deciding factor between them.
Which has the larger context window, Claude Fable 5.1 or GPT-6 Astra?
GPT-6 Astra accepts 1.05M tokens against 1M for Claude Fable 5.1. This only matters if you routinely send very long documents or large codebases.
Do Claude Fable 5.1 and GPT-6 Astra support the same reasoning levels?
Claude Fable 5.1 exposes adaptive, while GPT-6 Astra exposes low, medium, high, xhigh, max.
Should I use Claude Fable 5.1 or GPT-6 Astra?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Fable 5.1 suits frontier agents; GPT-6 Astra suits computer-use agents.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Context: GPT-6 Astra takes 1.05M against 1M for Claude Fable 5.1 — only decisive if your prompts approach the smaller window.
- Measured capability: Claude Fable 5.1 leads Artificial Analysis Intelligence Index 66 to 61.2 (measured 2026-08-14).
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.