Claude Fable 5.1 vs GPT-6 Astra vs Muse Spark Open
Too close to call on our weighted score (GPT-6 Astra 68, Muse Spark Open 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
OpenAIGPT-6 Astra
68/100- ECI169.1
- Price$10.00 / $50.00
- Context1.05M
MetaMuse Spark Open
68/100- ECI155.1
- Price$1.25 / $4.25
- Context1.05M
Too close to call
It is close. Our weighted score puts them within a point (GPT-6 Astra 68/100, Muse Spark Open 68/100, Claude Fable 5.1 66/100), so choose by what matters most for your work: GPT-6 Astra for raw capability and Muse Spark Open 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 · Muse Spark Open 155.1
- Lowest priceMuse Spark OpenMuse Spark Open $2.00 · Claude Fable 5.1 $20.00 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 Astra and Muse Spark OpenGPT-6 Astra 1,050,000 · Muse Spark Open 1,048,576 · Claude Fable 5.1 1,000,000 tokens
- Widest inputsMuse Spark OpenClaude Fable 5.1: Text, Images, PDFs · GPT-6 Astra: Text, Images, PDFs · Muse Spark Open: Text, Images, Audio, Video
- Self-hostingMuse Spark OpenPublishes downloadable weights (Muse Model License)
| Measure | Weight | Claude Fable 5.1 | GPT-6 Astra | Muse Spark Open |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 97 | 100 | 83 |
| Price | 25% | 0 | 0 | 34 |
| Inputs & features | 15% | 80 | 80 | 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 | GPT-6 AstraOpenAI | Muse Spark OpenMeta |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 166.4 | 169.1 (best) | 155.1 |
| ECI rank | #6 of 165 | #1 of 165 (best) | #39 of 165 |
| GPQA DiamondGraduate-level science questions | — | 95.8% (best) | 88.6% |
| FrontierMath Tiers 1–3Research-level mathematics | 90.2% | 93.7% (best) | 69.8% |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% (best) | 100% (best) | 98.1% |
| SimpleQA VerifiedShort factual questions | 70.8% | 75.6% (best) | 56.6% |
| Price per million tokens | |||
| Input | $10.00 | $10.00 | $1.25 (best) |
| Output | $50.00 | $50.00 | $4.25 (best) |
| Cached input | $0.25 (best) | $1.00 | — |
| Blended (3:1) | $20.00 | $20.00 | $2.00 (best) |
| Long-context rate | Same rate | Over 272K: $20.00 / $75.00 | Same rate |
| Price source | Official Anthropic API | Official OpenAI API | Median of 16 providers |
| Limits | |||
| Context window | 1,000,000 tokens | 1,050,000 tokens (best) | 1,048,576 tokens |
| Max output | 128,000 tokens | 128,000 tokens | 131,072 tokens (best) |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | No |
| Audio | No | No | Yes |
| Video | No | No | Yes |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | No |
| Availability | |||
| Weights | Proprietary | Proprietary | OpenMuse Model License |
| API model ID | claude-fable-5-1 | gpt-6-astra | — |
| API providers | 37 (best) | 37 (best) | 16 |
| Released | Sep 1, 2026 | Sep 4, 2026 | Oct 15, 2026 |
| Knowledge cutoff | Jun 2026 | Apr 30, 2026 | Jan 4, 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
- GPT-6 Astra$200.00
- Muse Spark Open$21.00
Which should you choose?
Which is better: Claude Fable 5.1, GPT-6 Astra or Muse Spark Open?
It is close. Our weighted score puts them within a point (GPT-6 Astra 68/100, Muse Spark Open 68/100, Claude Fable 5.1 66/100), so choose by what matters most for your work: GPT-6 Astra for raw capability and Muse Spark Open on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Claude Fable 5.1, GPT-6 Astra or Muse Spark Open?
Muse Spark Open is cheaper at $1.25 input / $4.25 output per million tokens (median across 16 API providers). 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 $2.00 per million tokens for Muse Spark Open versus $20.00 for Claude Fable 5.1 (10× as much) and $20.00 for GPT-6 Astra (10× 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 Muse Spark Open 155.1 (#39 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%, Muse Spark Open 69.8%; OTIS Mock AIME 2024–2025 — Claude Fable 5.1 100%, GPT-6 Astra 100%, Muse Spark Open 98.1%; SimpleQA Verified — GPT-6 Astra 75.6%, Claude Fable 5.1 70.8%, Muse Spark Open 56.6%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Fable 5.1, GPT-6 Astra and Muse Spark Open 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 Muse Spark Open 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, GPT-6 Astra up to 128,000, Muse Spark Open up to 131,072 tokens.
Which can read images, PDFs, audio or video?
Claude Fable 5.1 accepts text, images and PDFs; GPT-6 Astra accepts text, images and PDFs; Muse Spark Open accepts text, images, audio and video. Muse Spark Open handles the widest range of inputs.
Are any of these open source?
Muse Spark Open publishes its weights (Muse Model License) and can be self-hosted; Claude Fable 5.1 and GPT-6 Astra is proprietary.
Which is newer?
Muse Spark Open is the newest, released Oct 15, 2026. GPT-6 Astra came out Sep 4, 2026; Claude Fable 5.1 came out Sep 1, 2026. Knowledge cutoff: Claude Fable 5.1 Jun 2026, GPT-6 Astra Apr 30, 2026, Muse Spark Open Jan 4, 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.
