In PEP 694: Upload 2.0 API for Python Package Repositories, it states that unlike this PEP, the new upload API uses a new endpoint.
Unlike PEP 691, this PEP does not change the existing
1.0API in any way, so servers will be required to host the new API described in this PEP at a different endpoint than the existing upload API.
Why was the upload API chosen to be a separate endpoint, while the JSON API focuses on a single endpoint differentiated by headers (with the option of course to point at different endpoints per format)? It’s definitely more natural to use a different endpoint for new upload semantics, but that same argument could be applied to the new download API as well.