Claude Fable 5.1 vs GLM-5.3-Flash vs GPT-6 Luna
GPT-6 Luna comes out ahead, 83 to 77 and 66 on our weighted score, and it is the cheaper option too.
AnthropicClaude Fable 5.1
66/100- ECI164.8
- Price$10.00 / $50.00
- Context1M
Z.ai (Zhipu)GLM-5.3-Flash
77/100- ECI151.9
- Price$0.15 / $0.50
- Context1M
- Our pick
OpenAIGPT-6 Luna
83/100- ECI—
- Price$0.10 / $0.50
- Context1.05M
GPT-6 Luna is our pick
GPT-6 Luna is the better all-round choice, scoring 83/100 against GLM-5.3-Flash (77) and Claude Fable 5.1 (66). It leads on price. Claude Fable 5.1 wins on capability. GLM-5.3-Flash wins on inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (FrontierMath Tiers 1–3 and OTIS Mock AIME 2024–2025), because GPT-6 Luna has no Capabilities Index score yet.
- CapabilityClaude Fable 5.1Shared benchmarks: Claude Fable 5.1 95.1% · GPT-6 Luna 88.9% · GLM-5.3-Flash 74.8%
- Lowest priceGPT-6 LunaGPT-6 Luna $0.20 · GLM-5.3-Flash $0.237 · Claude Fable 5.1 $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 LunaGPT-6 Luna 1,050,000 · Claude Fable 5.1 1,000,000 · GLM-5.3-Flash 1,000,000 tokens
- Widest inputsGLM-5.3-FlashClaude Fable 5.1: Text, Images, PDFs · GLM-5.3-Flash: Text, Images, PDFs, Video · GPT-6 Luna: Text, Images, PDFs
- Self-hostingGLM-5.3-FlashPublishes downloadable weights
| Measure | Weight | Claude Fable 5.1 | GLM-5.3-Flash | GPT-6 Luna |
|---|---|---|---|---|
| CapabilityShared benchmarks | 50% | 95 | 75 | 89 |
| Price | 25% | 0 | 79 | 83 |
| Inputs & features | 15% | 80 | 90 | 80 |
| Context window | 10% | 60 | 60 | 61 |
| Overall | 100% | 66/100 | 77/100 | 83/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Fable 5.1Anthropic | GLM-5.3-FlashZ.ai (Zhipu) | GPT-6 LunaOpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 164.8 (best) | 151.9 | — |
| ECI rank | #4 of 148 (best) | #42 of 148 | — |
| GPQA DiamondGraduate-level science questions | — | 90.2% | 90.5% (best) |
| FrontierMath Tiers 1–3Research-level mathematics | 90.2% (best) | 55.8% | 79.0% |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% (best) | 93.9% | 98.9% |
| SimpleQA VerifiedShort factual questions | 70.8% (best) | — | 41.4% |
| Price per million tokens | |||
| Input | $10.00 | $0.15 | $0.10 (best) |
| Output | $50.00 | $0.50 (best) | $0.50 (best) |
| Cached input | $0.25 | $0.03 | $0.01 (best) |
| Blended (3:1) | $20.00 | $0.237 | $0.20 (best) |
| Long-context rate | Same rate | Same rate | Over 272K: $0.20 / $0.75 |
| Price source | Official Anthropic API | Official Z.AI API | Official OpenAI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,000,000 tokens | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | 131,072 tokens (best) | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | Yes |
| Audio | No | No | No |
| Video | No | Yes | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · high · max | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Open | Proprietary |
| API model ID | claude-fable-5-1 | glm-5.3-flash | gpt-6-luna |
| API providers | 29 | 65 (best) | 24 |
| Released | Sep 1, 2026 | Aug 26, 2026 | Sep 22, 2026 |
| Knowledge cutoff | Jun 2026 | — | May 18, 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
- GLM-5.3-Flash$2.50
- GPT-6 Luna$2.00
Which should you choose?
Which is better: Claude Fable 5.1, GLM-5.3-Flash or GPT-6 Luna?
GPT-6 Luna is the better all-round choice, scoring 83/100 against GLM-5.3-Flash (77) and Claude Fable 5.1 (66). It leads on price. Claude Fable 5.1 wins on capability. GLM-5.3-Flash wins on inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (FrontierMath Tiers 1–3 and OTIS Mock AIME 2024–2025), because GPT-6 Luna has no Capabilities Index score yet.
Which is cheaper, Claude Fable 5.1, GLM-5.3-Flash or GPT-6 Luna?
GPT-6 Luna is cheaper at $0.10 input / $0.50 output per million tokens (official OpenAI API price). GLM-5.3-Flash costs $0.15 input / $0.50 output per million tokens (official Z.AI API price); Claude Fable 5.1 costs $10.00 input / $50.00 output per million tokens (official Anthropic API price). At a typical mix of three input tokens to one output token, that is $0.20 per million tokens for GPT-6 Luna versus $0.237 for GLM-5.3-Flash (1.2× as much) and $20.00 for Claude Fable 5.1 (100× as much).
Which scores higher on benchmarks?
Not every model here has a Capabilities Index score, so we compare the average of shared benchmarks (FrontierMath Tiers 1–3 and OTIS Mock AIME 2024–2025): Claude Fable 5.1 95.1%, GPT-6 Luna 88.9% and GLM-5.3-Flash 74.8%. On individual benchmarks: FrontierMath Tiers 1–3 — Claude Fable 5.1 90.2%, GPT-6 Luna 79.0%, GLM-5.3-Flash 55.8%; OTIS Mock AIME 2024–2025 — Claude Fable 5.1 100%, GPT-6 Luna 98.9%, GLM-5.3-Flash 93.9%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Fable 5.1, GLM-5.3-Flash and GPT-6 Luna yet, so there is no like-for-like coding score. On overall capability, Claude Fable 5.1 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 Luna has the largest context window at 1,050,000 tokens, against 1,000,000 for Claude Fable 5.1 and 1,000,000 for GLM-5.3-Flash. Maximum output per response: Claude Fable 5.1 up to 128,000, GLM-5.3-Flash up to 131,072, GPT-6 Luna up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Fable 5.1 accepts text, images and PDFs; GLM-5.3-Flash accepts text, images, PDFs and video; GPT-6 Luna accepts text, images and PDFs. GLM-5.3-Flash handles the widest range of inputs.
Are any of these open source?
GLM-5.3-Flash publishes its weights and can be self-hosted; Claude Fable 5.1 and GPT-6 Luna is proprietary.
Which is newer?
GPT-6 Luna is the newest, released Sep 22, 2026. Claude Fable 5.1 came out Sep 1, 2026; GLM-5.3-Flash came out Aug 26, 2026. Knowledge cutoff: Claude Fable 5.1 Jun 2026, GPT-6 Luna May 18, 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 Oct 4, 2026.
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