Processing a job request for multiple versions of a distributed computing service. The service processing node does this by at least interleavingly (e.g., via time sharing with rapid context switching, or by actually concurrently) running a first runtime library associated with a first service version of the distributed computerized service and a second runtime library associated with a different service version of the distributed computerized service. While running the first runtime library, job requests of a first service version may be at least partially processed using a first set of one or more executables that interact with the first runtime library. While running the second runtime library, job requests of a second service version may be at least partially processed using a second set of one or more executables that interact with the second runtime library.