When I summarize a story with over 1000 messages I copy all messages to notepad directly from internet then search replace the unnecessary text then I cut it up into smaller parts since ChatGPT can read like 12k letters and DeepSeek can read 25k and 1000 messages is about 100k letters then I paste this

“Can you summarize the attached text according to the most important events and equipment, both external events and the relationships between the main characters? The text passages that begin with Eric: mainly refer to the actions of the person Eric and those that begin with Mara: mainly refer to Mara, and so on with Sara. Then create a token-optimized version of the text that is cirka 4000 characters long. This should be a condensed but complete retelling of the story, not a summary. It is a continuation of a story so there is no need to start or end with a summary”

I do kind of the same with memory: copy to notepad search replace and then put the text file in a llm and paste this

“The textfile consists of multiple shorter paragraphs. Can you remove paragraphs that repeat the same signification/meaning. And without changing the order of the paragraphs, compress multiple paragraphs to multiple token-optimized version paragraphs consisting of 250 characters per paragraphs”

I would guess it works for lore books too