There shouldn’t be a need for something like K.clear_session() since the graph should be automatically freed as long as there are no more references to it. So if model is the last variable referencing your graph, something like del model should do the trick. You might not even need del if model goes out of scope or you rebind your model variable to a new object.
If you find your memory usage still going up, you can add a call to gc.collect() to manually trigger python’s garbage collector. This might be necessary if your code isn’t CPU memory intensive.