If you want to do that, I have a model trained specifically on a dataset of building recursive summaries. Some of my training documents are 40-50k tokens.

https://huggingface.co/Tostino/Inkbot-13B-8k-0.2

Just chunk your document up, and pass in the prior summary along with this chunk of text, you can mention that it is chunk X of Y if you want (which can help with how it starts the summary often).

No. This does nothing to the context length itself which is still a sliding window.