Sitecore 9.1 has been released, but I can't see the 9.1 packages in my normal NuGet feed. Are they not released yet, or has something changed?
Sitecore did have 9.1 in its own feed to more closely match the way Sitecore does builds internally.
But Sitecore heard feedback from the community and the decision was made to move it back into a feed where multiple versions will be together. This will classify all the Sitecore dlls together under the same release version. And will make upgrading easy with the fact that all 9.x versions will be together.