Hi aclifton314,
Short answer: I’ve no idea - what happens if you try that?
I’ve not tried using Trainer or GPT2 (I’ve been using Bert with native pytorch commands), so I could easily be wrong here.   Please ignore anything where you know better.
In the Trainer documentation, it looks like from_pretrained is the correct command to use.
Did you set output_dir in your Trainer training arguments?  Have you checked that your trained model exists in your /path/to/model/ directory?
I don’t think you can import your custom model class (I think you will need to include your code to define it).
If you are not altering the shape of the model, do you need a custom model class?
I think you might need to import GPT2LMHeadModel, whether you use it as-is or by inheriting.
I think you might need to use tokenizer.tokenize() or tokenizer.encode_plus() or something like that, rather than just tokenizer()