Thanks to https://github.com/YaleDHLab via #275, gpt-2-simple now supports TensorFlow 2 by default, and the minimum TensorFlow version is now 2.5.1! The Colab Notebook has also been update to no longer use TensorFlow 1.X.
Note: Development on gpt-2-simple has mostly been superceded by aitextgen, which has similar AI text generation capabilities with more efficient training time and resource usage. If you do not require using TensorFlow, I recommend using aitextgen instead. Checkpoints trained using gpt-2-simple can be loaded using aitextgen as well.