The current 5.1.8 release ships with KaTeX version 0.2.0. I've just upgraded to KaTeX 0.4.3 for TiddlyWiki 5.1.9 which is available for preview:
Please don't start using the prerelease version for anything important! It's just for evaluation until it is released. We've had instances of users losing data as a result of ignoring these warnings...
I've also added the KaTeX version number to the readme for the KaTeX plugin. In 5.1.9, go to Control Panel, locate the KaTeX plugin in the plugin list, and click the triangle to reveal the readme.
Best wishes
Jeremy.