What is the difference between T5Model, T5WithLMHeadModel, T5PreTrainedModel?
## ❓ Questions & Help

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I notice that for T5 model, there are more choices(T5Model, T5WithLMHeadModel, T5PreTrainedModel) than BERT or GPT. What is the difference between these three? I think all three are pre-trained model. We do not use T5PreTrainedModel in our downstream task code. Besides, the difference between T5Model and T5WithLMHeadModel is that the latter contains one more linear layer at the end.   Am I right about these?
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