Here you will find a few very fast implementations of the jupyter notebook strip out tools.
They focus on being fast git strip out filters, without much else.
As of this writing nbstripout-fast and nbstripout-jq are respectively 13 and 9 times faster than nbstripout with the notebooks I tested them with.
If you need the full functionality see nbstripout.
These are provided as is. Help yourself to them, modify them to your needs, but please do not ask for new features, etc. Use the well-maintained and supported nbstripout for feature requests.