Notebook is now shipped in http://Copilot.microsoft.com, on both PC and mobile browser. It’s a new interface for crafting, improving, and revising your prompts without chat dialogue. Ideal when you need to iterate on a prompt to get the best result. It supports up to 18K characters.
At the present time, there are pros and cons of (the original) Copilot vs Notebook:
Copilot has the plugins vs no plugins for Notebook.
Copilot has choices of conversation styles vs no choices for Notebook
Copilot has chat history for reiterating your prompts vs doing VERY extensive reiterations right in the prompt window of Notebook (very convenient indeed)
Copilot can produce drawings vs Notebook promising to produce drawings but does not produce the drawings (the content window goes blank)
There may be more bullet points, and the bullet points may change very, very rapidly.