# Claude Fable 5.1 vs GPT-6 Luna

GPT-6 Luna is the cheaper of the 2: for the same tokens, 3 read for each 1 written, Claude Fable 5.1 costs 100 times as much. Below are both price lists, what 8 everyday jobs cost a month on each, and how many tokens the same text takes on each, which can change the answer.

- Page, with a calculator for your own job: https://tecyfy.com/prices/compare/claude-fable-5-1-vs-gpt-6-luna
- Makers: Claude Fable 5.1 from Anthropic, GPT-6 Luna from OpenAI

## Price per million tokens, in US dollars

| | Claude Fable 5.1 | GPT-6 Luna |
| --- | --: | --: |
| Input | $10 | $0.10 |
| Cached input | $0.25 | $0.01 |
| Cache write | $12.50 | $0.125 |
| Output | $50 | $0.50 |
| Blend, 3 read for each 1 written | $20 | $0.20 |
| Batch input | $5 | $0.05 |
| Batch output | $25 | $0.25 |
| Long prompt input (above 272K on GPT-6 Luna) | $10 | $0.20 |
| Long prompt output | $50 | $0.75 |
| Context window, tokens | 1M | 1.05M |
| Capability score (Epoch Capabilities Index; GPT-5 is 150) | 165 | 156 |
| Longest answer, tokens | 128K | 128K |

## The same text, counted by each maker

Our lesson "How AI writes" (https://tecyfy.com/learn/how-ai-works/how-ai-writes), about 1,700 words of English:

- Claude Fable 5.1: about 2,100 to 3,600 tokens. Anthropic does not publish its tokenizer. It says Claude 4.7 and later produce about 30 percent more tokens for the same text than earlier models, and an independent test counted TypeScript at 1.73 times OpenAI's figure. The range runs from OpenAI's count to 1.75 times it.
- GPT-6 Luna: about 2,100 tokens. GPT-5.6 is counted with o200k_base, the tokenizer OpenAI publishes for it, so its count is exact. OpenAI has not published the tokenizer of GPT-6, so its count is the same o200k_base figure, marked as about.

## What 8 everyday jobs cost a month on each

Each job at its usual runs a day, for 30 days, at the standard price.

| Job | Tokens in, out, runs a day | Claude Fable 5.1 | GPT-6 Luna |
| --- | --- | --: | --: |
| A chat question | 300, 500, 100 | $84.00 | 84 cents |
| A hard question, with thinking | 300, 1,400, 100 | $219 | $2.19 |
| A long report, summarised | 60,000, 2,000, 20 | $420 | $4.20 |
| A 40-turn agent task | 2,800,000, 40,000, 10 | $1,629 | $21.96 |
| A support bot's reply | 4,000, 300, 2,000 | $2,130 | $22.20 |
| Sort a message into a category | 250, 5, 50,000 | $4,125 | $41.25 |
| Read an invoice into fields | 1,500, 250, 1,000 | $825 | $8.25 |
| Review a pull request | 25,000, 4,500, 50 | $713 | $7.13 |

## Questions

### Which is cheaper, Claude Fable 5.1 or GPT-6 Luna?

GPT-6 Luna is cheaper: $0.10 per million tokens read and $0.50 per million written, against $10 and $50 on Claude Fable 5.1. On a mix of 3 tokens read for each 1 written, Claude Fable 5.1 costs 100 times as much.

### Which is better, Claude Fable 5.1 or GPT-6 Luna?

On the Epoch Capabilities Index, an independent score from Epoch AI that combines over 50 benchmarks, Claude Fable 5.1 scores 165 and GPT-6 Luna 156, above the top of the range of doubt around GPT-6 Luna's score (GPT-5 is 150). One score is an average; test both on your own work before you switch.

### What does a support bot cost a month on Claude Fable 5.1 and GPT-6 Luna?

At 2,000 replies a day, each reading 4,000 tokens (50 percent of them from cache) and writing 300, it costs $2,130 a month on Claude Fable 5.1 and $22.20 on GPT-6 Luna: Claude Fable 5.1 costs 96 times as much for this job.

### What does an AI agent task cost on Claude Fable 5.1 and GPT-6 Luna?

One 40-turn task that reads 2,800,000 tokens in all, 90 percent of them from cache, and writes 40,000, costs $5.43 on Claude Fable 5.1 and 7.3 cents on GPT-6 Luna. At 10 tasks a day that is $1,629 and $21.96 a month.

### Which has the larger context window, Claude Fable 5.1 or GPT-6 Luna?

GPT-6 Luna, with 1.05M tokens against 1M on Claude Fable 5.1. The window holds your instructions, the files you attach, the conversation so far and the answer, all at once.

### Does the same text take the same number of tokens on Claude Fable 5.1 and GPT-6 Luna?

No. Our lesson "How AI writes", 1,700 words long, is about 2,100 to 3,600 tokens on Claude Fable 5.1 and about 2,100 on GPT-6 Luna. Each maker cuts text its own way, and every extra token is paid for at the model's price.

### Can I pay less on Claude Fable 5.1 and GPT-6 Luna for work that can wait?

Yes, on both. With a batch, where you collect the answers later instead of at once, Claude Fable 5.1 costs $5 per million tokens read and $25 written, and GPT-6 Luna $0.05 and $0.25.

## Sources

- [Anthropic: API prices](https://platform.claude.com/docs/en/about-claude/pricing)
- [OpenAI: API prices](https://developers.openai.com/api/docs/pricing)
- [Epoch Capabilities Index, by Epoch AI (CC BY 4.0)](https://epoch.ai/benchmarks/eci)

## Other comparisons

- [GPT-6 Luna vs GPT-6 Sol](https://tecyfy.com/prices/compare/gpt-6-luna-vs-gpt-6-sol.md)
- [GPT-5.6 Sol vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-6-sol-vs-gpt-6-luna.md)
- [GPT-5.6 Terra vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-6-terra-vs-gpt-6-luna.md)
- [GPT-5.6 Luna vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-6-luna-vs-gpt-6-luna.md)
- [GPT-5.5 vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-5-vs-gpt-6-luna.md)
- [GPT-5.5 pro vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-5-pro-vs-gpt-6-luna.md)