Guide
How many tokens is a book?
An 80,000-word novel is about 106,400 tokens. A 100,000-word non-fiction book is about 133,000.
What it costs to summarize one
Assume the full text goes in and a summary of about 21,280 tokens (20%) comes out:
| Model | Input cost | Output cost | Total |
|---|---|---|---|
| GPT-6.1 Sol | $0.2128 | $0.2128 | $0.4256 |
| Claude Sonnet 5.5 | $0.2128 | $0.2128 | $0.4256 |
| Gemini 3.8 Flash | $0.0798 | $0.0798 | $0.1596 |
| GPT-6 Luna | $0.0106 | $0.0106 | $0.0213 |
Two lessons: the summary is cheap because the book is mostly input tokens, and the cheapest model is about 20× cheaper than the mid-range models for the same job. The expensive question is not “can I afford to summarize a book” — it is “can I afford to do it 10,000 times”. That is where model choice, not prompt cleverness, moves the bill.
Check your own document in the token counter before sending a book-length prompt anywhere.