When calling glGetProgramPipelineiv with pname=GL_COMPUTE_SHADER, an error is reported saying that enum (GL_COMPUTE_SHADER = 0x91b9) is invalid. None of the other shader stage enums report a problem.
The spec says that all enums in Table 7.1 which includes GL_COMPUTE_SHADER are valid for use, and should return the program associated with that stage.