Context
We would like to have client side rendering with vector tiles, backed by the tegola vector tile server. This would help with internationalisation, simplify hosting multiple styles, and avoid having to use @2.png retina screen PNG tiles. We have some level of Vector Tile support internally, but this never made it to production for client side rendering.
For anyone interested in working on this:
We used to have an endpoint. (without styling) for vector tiles, but it never made it to the level of 'being supported'
It was something like: https://maps.wikimedia.org/osm-pbf/{z}/{x}/{y}.pbf and it is still in the docker config for Kartotherian. https://gerrit.wikimedia.org/g/mediawiki/services/kartotherian/+/148400384313afad30034e79239f3a8c555a42a6/sources.docker.yaml#57
In 2021, there was some benchmarking and other exploratory work done as part of T269690#7503367, including a patch to Kartographer to implement a client side solution.