You need all the same stuff with a REST API only instead of using tooling to codegen all the boilerplate you have to write it by hand (or use janky OpenAPI code generators which, in my experience, rarely work very well).

I am increasingly annoyed by protobuf as a standalone format but given the choice to create a new API using gRPC (where I can spend five minutes writing some proto files and then codegen all the boilerplate I need for both server and client in any mainstream language) and creating it as a REST API where I have to manually code all the boilerplate and decide between a zillion different ways of doing everything I will choose gRPC 100% of the time.