I ran python3 -m pip install -U discord.py but it only installed discord.py v0.16.x. How do I install the new discord.py rewrite v1.0? 
I uninstalled the old discord.py using pip uninstall discord.py and re-ran pip to install discord.py, only to get version v0.16.x again instead of the new v1.0 version.
pip install discord.py
Installing from the source[branch:master] is not recommended since it is in the testing phase(Writing as of 5/30/2021).If you want to test out  buttons then sure go ahead and run pip install -U git+https://github.com/Rapptz/discord.py@master
How to install discord.py rewrite?