Drafts that start from a long document now arrive about twice as fast. The assistant reads the document in parts and starts writing as soon as the first part is ready, instead of waiting for the whole file.
Before this change the assistant read the entire document first and only then began the draft. On a short note nobody noticed. On a forty-page report, the wait before the first word could run to half a minute.
What changed
The document is split into sections and read in order. As soon as the opening sections give enough to start, the draft begins to stream, and the rest of the document is read while you are already reading the first lines.
What did not change
The assistant still reads everything before it finishes. If a later section changes the picture, the draft is corrected before it is complete, so the final text is based on the whole document, as before.
You do not need to turn anything on. The speed-up applies to every draft that starts from an attached document or a long pasted text.