You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.

nautobot
1.6.0rc1

This version was deleted from PyPI around 2023-11-15. Installing fails with:
$ pip3 install nautobot==1.6.0rc1 ERROR: Could not find a version that satisfies the requirement nautobot==1.6.0rc1
View other deleted versions of nautobot

Install through StableBuild

You can install this package from StableBuild's PyPI snapshots from before the version was deleted:
pip3 install \ -i https://YOUR_API_KEY.pypimirror.stablebuild.com/2023-11-14/ \ nautobot==1.6.0rc1
Sign up for StableBuild to get an API key (it's free and takes <60 seconds!)

Or, download files manually

And install manually via pip:
nautobot-1.6.0rc1-py3-none-any.whl (85.3MB)
nautobot-1.6.0rc1.tar.gz (84.5MB)