Claude Fable 5.1 vs Inkling Small vs GPT-6 Astra
Too close to call on our weighted score (Inkling Small 68, GPT-6 Astra 68, Claude Fable 5.1 66). The right pick depends on what you value most.
AnthropicClaude Fable 5.1
66/100- ECI166.4
- Price$10.00 / $50.00
- Context1M
Thinking MachinesInkling Small
68/100- ECI150.5
- Price$0.58 / $1.44
- Context1.05M
OpenAIGPT-6 Astra
68/100- ECI169.1
- Price$10.00 / $50.00
- Context1.05M
Too close to call
It is close. Our weighted score puts them within a point (Inkling Small 68/100, GPT-6 Astra 68/100, Claude Fable 5.1 66/100), so choose by what matters most for your work: GPT-6 Astra for raw capability and Inkling Small on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGPT-6 AstraCapabilities Index (ECI): GPT-6 Astra 169.1 · Claude Fable 5.1 166.4 · Inkling Small 150.5
- Lowest priceInkling SmallInkling Small $0.795 · Claude Fable 5.1 $20.00 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 Astra and Inkling SmallGPT-6 Astra 1,050,000 · Inkling Small 1,048,576 · Claude Fable 5.1 1,000,000 tokens
- Widest inputsSame inputsClaude Fable 5.1: Text, Images, PDFs · Inkling Small: Text, Images, Audio · GPT-6 Astra: Text, Images, PDFs
- Self-hostingInkling SmallPublishes downloadable weights (Apache-2.0)
| Measure | Weight | Claude Fable 5.1 | Inkling Small | GPT-6 Astra |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 97 | 77 | 100 |
| Price | 25% | 0 | 52 | 0 |
| Inputs & features | 15% | 80 | 70 | 80 |
| Context window | 10% | 60 | 61 | 61 |
| Overall | 100% | 66/100 | 68/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Fable 5.1Anthropic | Inkling SmallThinking Machines | GPT-6 AstraOpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 166.4 | 150.5 | 169.1 (best) |
| ECI rank | #6 of 165 | #58 of 165 | #1 of 165 (best) |
| GPQA DiamondGraduate-level science questions | — | 88.5% | 95.8% (best) |
| FrontierMath Tiers 1–3Research-level mathematics | 90.2% | 46.3% | 93.7% (best) |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% (best) | 90.0% | 100% (best) |
| SimpleQA VerifiedShort factual questions | 70.8% | 19.1% | 75.6% (best) |
| Price per million tokens | |||
| Input | $10.00 | $0.58 (best) | $10.00 |
| Output | $50.00 | $1.44 (best) | $50.00 |
| Cached input | $0.25 | $0.116 (best) | $1.00 |
| Blended (3:1) | $20.00 | $0.795 (best) | $20.00 |
| Long-context rate | Same rate | Same rate | Over 272K: $20.00 / $75.00 |
| Price source | Official Anthropic API | Official Thinking Machines API | Official OpenAI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,048,576 tokens | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | 1,048,576 tokens (best) | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | No | Yes |
| Audio | No | Yes | No |
| Video | No | No | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | No | Yes |
| Availability | |||
| Weights | Proprietary | OpenApache-2.0 | Proprietary |
| API model ID | claude-fable-5-1 | thinkingmachines/Inkling-Small | gpt-6-astra |
| API providers | 37 (best) | 12 | 37 (best) |
| Released | Sep 1, 2026 | Jul 30, 2026 | Sep 4, 2026 |
| Knowledge cutoff | Jun 2026 | — | Apr 30, 2026 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Claude Fable 5.1$200.00
- Inkling Small$8.68
- GPT-6 Astra$200.00
Which should you choose?
Which is better: Claude Fable 5.1, Inkling Small or GPT-6 Astra?
It is close. Our weighted score puts them within a point (Inkling Small 68/100, GPT-6 Astra 68/100, Claude Fable 5.1 66/100), so choose by what matters most for your work: GPT-6 Astra for raw capability and Inkling Small on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Claude Fable 5.1, Inkling Small or GPT-6 Astra?
Inkling Small is cheaper at $0.58 input / $1.44 output per million tokens (official Thinking Machines API price). Claude Fable 5.1 costs $10.00 input / $50.00 output per million tokens (official Anthropic API price); GPT-6 Astra costs $10.00 input / $50.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $0.795 per million tokens for Inkling Small versus $20.00 for Claude Fable 5.1 (25× as much) and $20.00 for GPT-6 Astra (25× as much).
Which scores higher on benchmarks?
GPT-6 Astra scores higher on the Capabilities Index (ECI): GPT-6 Astra 169.1 (#1 of 165), Claude Fable 5.1 166.4 (#6 of 165) and Inkling Small 150.5 (#58 of 165). The confidence ranges of the top two overlap (165.9–174.3 vs 163.6–170.8), so treat the gap as small. On individual benchmarks: FrontierMath Tiers 1–3 — GPT-6 Astra 93.7%, Claude Fable 5.1 90.2%, Inkling Small 46.3%; OTIS Mock AIME 2024–2025 — Claude Fable 5.1 100%, GPT-6 Astra 100%, Inkling Small 90.0%; SimpleQA Verified — GPT-6 Astra 75.6%, Claude Fable 5.1 70.8%, Inkling Small 19.1%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Fable 5.1, Inkling Small and GPT-6 Astra yet, so there is no like-for-like coding score. On overall capability, GPT-6 Astra leads, which tends to carry over to coding, but test on your own codebase. All three support tool calling for agent workflows.
Which has the bigger context window?
GPT-6 Astra and Inkling Small have the largest context windows (1,050,000 and 1,048,576 tokens), against 1,000,000 for Claude Fable 5.1. Maximum output per response: Claude Fable 5.1 up to 128,000, Inkling Small up to 1,048,576, GPT-6 Astra up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Fable 5.1 accepts text, images and PDFs; Inkling Small accepts text, images and audio; GPT-6 Astra accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
Inkling Small publishes its weights (Apache-2.0) and can be self-hosted; Claude Fable 5.1 and GPT-6 Astra is proprietary.
Which is newer?
GPT-6 Astra is the newest, released Sep 4, 2026. Claude Fable 5.1 came out Sep 1, 2026; Inkling Small came out Jul 30, 2026. Knowledge cutoff: Claude Fable 5.1 Jun 2026, GPT-6 Astra Apr 30, 2026.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Nov 2, 2026.
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