Accessing Estimator evaluation results via SessionRunHooks

I'm trying to modify a program that uses the Estimator class in TensorFlow (v1.10) and I would like to access the evaluation metric results every time evaluation occurs so that I can copy the checkpoint files only when a new maximum has been achieved.

One idea I had was to create a class inheriting from SessionRunHook, doing the work I want in the after_run method. According to the documentation I can specify what is passed to after_run using before_run. However I cannot find a way to access the evaluation metrics results I want from the information passed in to before_run.

I looked into the Estimator code and it appears that it is writing the results to a summary file so another idea I had was to read this back in the after_run method, but the summary api doesn't seem to provide any read operations.

Are there any other ways I can achieve what I want to do? Not using the Estimator class is not an option as that would involve drastic changes to the code I'm working with.

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