One task I do is I feed the models the text of entire books, and ask them various questions about it ('what happened in Chapter 4', 'what did character X do in the book' etc.).

GPT 4.1 is the first model that has provided a human-quality answer to these questions. It seems to be the first model that can follow plotlines, and character motivations accurately.

I'd say since text processing is a very important use case for LLMs, that's quite noteworthy.