Choose Anthropic: Claude Fable 5.1 if…
No advantage on the data we track — pick it for provider preference or output quality on your own prompts.
Anthropic: Claude Fable 5.1 vs OpenAI: GPT-5.6 Luna Pro
OpenAI: GPT-5.6 Luna Pro comes out ahead on the data we track: 2 advantages and none for Anthropic: Claude Fable 5.1.
Key numbers
| Spec | Anthropic: Claude Fable 5.1 | OpenAI: GPT-5.6 Luna Pro |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Input price (per 1M tokens) | $10.00 | $0.20 |
| Output price (per 1M tokens) | $50.00 | $1.20 |
| Blended price (3:1 input/output) | $20.00 | $0.45 |
| Cheaper than … of all models we track | 3% | 55% |
| Context window | 1M tokens (~1,500 pages) | 1.1M tokens (~1,575 pages) |
| Larger context than … of all models | 69% | 92% |
| Max output per response | 128K tokens (~96,000 words) | 128K tokens (~96,000 words) |
| Input types | text, image, file | file, image, text |
| Output types | text | text |
| Free variant | No | No |
| Listed since | 2026-09-01 | 2026-07-09 |
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What it costs for real workloads
Monthly cost at list price for five common workloads. Token counts per unit are stated so you can scale them to your own traffic. A workload that does not fit a model's context window is marked rather than priced.
| Workload (per month) | Anthropic: Claude Fable 5.1 | OpenAI: GPT-5.6 Luna Pro | Difference |
|---|---|---|---|
| Customer-support chatbot 50,000 conversations — each a 6-turn conversation (1,500 in / 400 out tokens) | $1,750 | $39.00 | OpenAI: GPT-5.6 Luna Pro saves $1,711 |
| RAG search over documents 20,000 questions — each a question answered from ~8 retrieved passages (6,000 in / 500 out tokens) | $1,700 | $36.00 | OpenAI: GPT-5.6 Luna Pro saves $1,664 |
| Coding / tool-using agent 2,000 tasks — each a multi-step task with tool calls and file context (60,000 in / 6,000 out tokens) | $1,800 | $38.40 | OpenAI: GPT-5.6 Luna Pro saves $1,762 |
| Batch summarisation 10,000 documents — each a 6,000-word report summarised to a page (8,000 in / 600 out tokens) | $1,100 | $23.20 | OpenAI: GPT-5.6 Luna Pro saves $1,077 |
| Long-document analysis 500 documents — each a 150-page contract or codebase read in one pass (100,000 in / 2,000 out tokens) | $550 | $11.20 | OpenAI: GPT-5.6 Luna Pro saves $539 |
Capabilities side by side
| Capability | Anthropic: Claude Fable 5.1 | OpenAI: GPT-5.6 Luna Pro | What it lets you do |
|---|---|---|---|
| Tool / function calling | ✓ Yes | ✓ Yes | call your APIs and run agent loops |
| Structured output (JSON schema) | ✓ Yes | ✓ Yes | return JSON that validates against your schema |
| Reasoning / thinking mode | ✓ Yes | ✓ Yes | spend extra tokens thinking before answering hard problems |
| Image input | ✓ Yes | ✓ Yes | read screenshots, charts and scanned pages |
| Audio input | — | — | take speech or audio directly |
| File / PDF input | ✓ Yes | ✓ Yes | accept documents without your own parsing step |
| Image output | — | — | generate images, not just text |
| Built-in web search | ✓ Yes | ✓ Yes | answer from live web results |
| Seed (reproducible sampling) | — | ✓ Yes | repeat a generation for tests and evals |
| Log-probabilities | — | — | read token confidence for classification and scoring |
From each model's published parameters and input/output types. “—” means not advertised, not proven absent.
Price history
- Anthropic: Claude Fable 5.1: price unchanged since we started tracking it on 2026-09-02.
- OpenAI: GPT-5.6 Luna Pro: input price raised 50% ($0.10 → $0.20/1M), output price raised 50% ($0.60 → $1.20/1M) on 2026-08-18.
| Date | Model | Input / 1M | Output / 1M |
|---|---|---|---|
| 2026-08-18 | OpenAI: GPT-5.6 Luna Pro | $0.20 | $1.20 |
Which should you choose?
Choose OpenAI: GPT-5.6 Luna Pro if…
- cost matters at scale — it is 98% cheaper on a typical 3:1 input/output mix ($39.00 vs $1,750 a month for 50,000 support chats)
- you need seed (reproducible sampling) — to repeat a generation for tests and evals; Anthropic: Claude Fable 5.1 does not advertise it
Frequently asked questions
Is Anthropic: Claude Fable 5.1 better than OpenAI: GPT-5.6 Luna Pro?
OpenAI: GPT-5.6 Luna Pro comes out ahead on the data we track: 2 advantages and none for Anthropic: Claude Fable 5.1.
Which is cheaper, Anthropic: Claude Fable 5.1 or OpenAI: GPT-5.6 Luna Pro?
OpenAI: GPT-5.6 Luna Pro is cheaper: $0.45 vs $20.00 per 1M tokens at a typical 3:1 input/output mix, 98% less. For 50,000 support conversations a month that is $39.00 against $1,750.
How much do Anthropic: Claude Fable 5.1 and OpenAI: GPT-5.6 Luna Pro cost per million tokens?
Anthropic: Claude Fable 5.1 costs $10.00 per 1M input tokens and $50.00 per 1M output tokens; OpenAI: GPT-5.6 Luna Pro costs $0.20 input and $1.20 output. Output tokens are billed separately, so long answers shift the gap.
Which has the bigger context window, Anthropic: Claude Fable 5.1 or OpenAI: GPT-5.6 Luna Pro?
OpenAI: GPT-5.6 Luna Pro: 1.1M tokens, about 1,575 pages, against 1M (about 1,500 pages) for Anthropic: Claude Fable 5.1.
Do Anthropic: Claude Fable 5.1 and OpenAI: GPT-5.6 Luna Pro support function calling and JSON output?
Tool calling — Anthropic: Claude Fable 5.1: yes, OpenAI: GPT-5.6 Luna Pro: yes. JSON-schema structured output — Anthropic: Claude Fable 5.1: yes, OpenAI: GPT-5.6 Luna Pro: yes.
Can Anthropic: Claude Fable 5.1 or OpenAI: GPT-5.6 Luna Pro read images?
Yes, both accept image input.
Is Anthropic: Claude Fable 5.1 or OpenAI: GPT-5.6 Luna Pro free to use?
No free variant is listed for either; both are pay-per-token.
What is the maximum output length of Anthropic: Claude Fable 5.1 and OpenAI: GPT-5.6 Luna Pro?
Anthropic: Claude Fable 5.1 can write up to 128K tokens (about 96,000 words) per response; OpenAI: GPT-5.6 Luna Pro up to 128K (about 96,000 words).
When were Anthropic: Claude Fable 5.1 and OpenAI: GPT-5.6 Luna Pro released?
Anthropic: Claude Fable 5.1 was listed on 2026-09-01; OpenAI: GPT-5.6 Luna Pro on 2026-07-09.
Has the price of Anthropic: Claude Fable 5.1 or OpenAI: GPT-5.6 Luna Pro changed?
Anthropic: Claude Fable 5.1: price unchanged since we started tracking it on 2026-09-02. OpenAI: GPT-5.6 Luna Pro: input price raised 50% ($0.10 → $0.20/1M), output price raised 50% ($0.60 → $1.20/1M) on 2026-08-18.
About the two models
Anthropic: Claude Fable 5.1
Claude Fable 5.1 improves on Claude Fable 5 across the board, with the biggest gains in agentic coding, long-running agentic workflows, and knowledge work: long code refactors, front-end and visual...
Full Anthropic: Claude Fable 5.1 specs →OpenAI: GPT-5.6 Luna Pro
GPT-5.6 Luna Pro is the same underlying model as [GPT-5.6 Luna](https://openrouter.ai/openai/gpt-5.6-luna), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. **Cost note:** pro mode spends far more...
Full OpenAI: GPT-5.6 Luna Pro specs →