Buck2 has support for persistent workers, however, these are only available for locally executed actions. In contrast, Bazel supports remote persistent workers, see also BuildBuddy docs.

Persistent workers can provide large performance benefits, the Bazel documentation reports 2-4x speed-ups for Java, preliminary experiments on our Haskell builds have shown about 3x speed-ups. Without support for persistent workers in remote execution environments, users have to make a trade-off between the speed-up provided by a persistent worker and the speed-up provided by scaling to many build nodes. It would be preferable if both speed-ups could be combined by supporting persistent workers in remote execution environments.