Earlier quoted context omitted.
The problem is that while you can train a model with the hyperparameter of "context size" set to 1M, there's very little 1M data to train on. Most of your model's ability to follow long context comes from the fact that it's trained on lots of (stolen) books; in fact I believe OpenAI just outright said in court that they can't do long context without training on books. Novels are usually measured in terms of words; an…
What about old books? Wikipedia? Law texts? Programming languages documentations? How many tokens is a 100 pages PDF? 10k to 100k?
For a 100 page book, that translates to around 50,000 tokens. For 1 mil+ tokens, we need to be looking at 2000+ page books. That's pretty rare, even for documentation.
It doesn't have to be text-based, though. I could see films and TV shows becoming increasingly important for long-context model training.