Why isn't there a SequenceClassificationModel for GPT-2 (and some other models)?
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Why isn't there a SequenceClassificationModel (like there is for BERT) for GPT-2? I was able to implement this pretty easily by adding a "[CLS]" token to the vocabulary (like in the GPT2DoubleHeadsModel), appending sequences with "[CLS]", and then adding a linear layer that maps from the embedding of "[CLS]" to a vector of logits corresponding to the classes. After training, this model worked comparably to BertSequenceClassificationModel for my use-case. It would be nice to have this model in the transformers library and not have to code it up from scratch. 

If this sounds like a good idea, I can make a pull request with a GPT2SequenceClassificationModel added. If not, why is it not a good idea? 
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
