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# Encoder Decoder Models

The [`EncoderDecoderModel`] can be used to initialize a sequence-to-sequence model with any
pretrained autoencoding model as the encoder and any pretrained autoregressive model as the decoder.

The effectiveness of initializing sequence-to-sequence models with pretrained checkpoints for sequence generation tasks
was shown in [Leveraging Pre-trained Checkpoints for Sequence Generation Tasks](https://arxiv.org/abs/1907.12461) by
Sascha Rothe, Shashi Narayan, Aliaksei Severyn.

After such an [`EncoderDecoderModel`] has been trained/fine-tuned, it can be saved/loaded just like
any other models (see the examples for more information).

An application of this architecture could be to leverage two pretrained [`BertModel`] as the encoder
and decoder for a summarization model as was shown in: [Text Summarization with Pretrained Encoders](https://arxiv.org/abs/1908.08345) by Yang Liu and Mirella Lapata.

The [`~TFEncoderDecoderModel.from_pretrained`] currently doesn't support initializing the model from a
pytorch checkpoint. Passing `from_pt=True` to this method will throw an exception. If there are only pytorch
checkpoints for a particular encoder-decoder model, a workaround is:

```python
>>> # a workaround to load from pytorch checkpoint
>>> _model = EncoderDecoderModel.from_pretrained("patrickvonplaten/bert2bert-cnn_dailymail-fp16")
>>> _model.encoder.save_pretrained("./encoder")
>>> _model.decoder.save_pretrained("./decoder")
>>> model = TFEncoderDecoderModel.from_encoder_decoder_pretrained(
...     "./encoder", "./decoder", encoder_from_pt=True, decoder_from_pt=True
... )
>>> # This is only for copying some specific attributes of this particular model.
>>> model.config = _model.config
```

This model was contributed by [thomwolf](https://github.com/thomwolf). This model's TensorFlow and Flax versions
were contributed by [ydshieh](https://github.com/ydshieh).


## EncoderDecoderConfig

[[autodoc]] EncoderDecoderConfig

## EncoderDecoderModel

[[autodoc]] EncoderDecoderModel
    - forward
    - from_encoder_decoder_pretrained

## TFEncoderDecoderModel

[[autodoc]] TFEncoderDecoderModel
    - call
    - from_encoder_decoder_pretrained

## FlaxEncoderDecoderModel

[[autodoc]] FlaxEncoderDecoderModel
    - __call__
    - from_encoder_decoder_pretrained
