As you might imagine, since the actual optimization task runs on a remote system in a Compute Server environment, Gurobi callbacks give different behavior than they do when the task runs locally. In particular, callbacks are both less frequent and more restrictive to avoid communication overhead and a loss in performance. You will only receive MESSAGE, BARRIER, SIMPLEX, MIP, MIPSOL and MULTIOBJ callbacks; you will not receive PRESOLVE or MIPNODE callbacks. As a result, you will only have access to a subset of the callback information that you would be able to obtain when running locally. In particular, it is not possible to import a solution via the respective routine (this is GRBcbsolution in C, GRBCallback::setSolution in C++, GRBCallback.setSolution in Java, GRBCallback.SetSolution in .NET, and Model.cbSetSolution in Python). You can still request that the optimization shall be terminated from any of the callbacks you receive, though. Please refer to the Callback Code section of the Gurobi Reference Manual for more information on the various callback codes.