Running into a similar issue with converting a frozen graph file. The unified coremltools API says it supports .pb format but still getting this error. NotImplementedError: Expected model format: [SavedModel | [concrete_function] | tf.keras.Model | .h5] Same as OP, i've tried all other approaches but they meet a dead end at some point or other. Any inputs from anyone else?

Plus import tensorflow in the script. import tensorflow as tf

This your environment does not have tensorflow installed while your script uses it. Install tensorflow package and run it again.