The simplicity of the encoder-decoder model is its clean separation of the encoder -which builds a representation of the source text -from the decoder, which uses this context to generate a target text. In the model as we've described it so far, this context vector is h n , the hidden state of the last (nth) time step of the source text. This final hidden state is thus acting as a bottleneck: it must represent absolutely everything about the meaning of the source text, since the only thing the decoder knows about the source text is what's in this context vector (Fig. 10.8) . Information at the beginning of the sentence, especially for long sentences, may not be equally well represented in the context vector.