    def from_archive(cls, archive_file: str, vocab: Vocabulary = None) -> "Model":
        """
        Loads a model from an archive file.  This basically just calls
        `return archival.load_archive(archive_file).model`.  It exists as a method here for
        convenience, and so that we can register it for easy use for fine tuning an existing model
        from a config file.

        If `vocab` is given, we will extend the loaded model's vocabulary using the passed vocab
        object (including calling `extend_embedder_vocab`, which extends embedding layers).
        """
        from allennlp.models.archival import load_archive  # here to avoid circular imports

        model = load_archive(archive_file).model
        if vocab:
            model.vocab.extend_from_vocab(vocab)
            model.extend_embedder_vocab()
        return model
Loads a model from an archive file.  This basically just calls
`return archival.load_archive(archive_file).model`.  It exists as a method here for
convenience, and so that we can register it for easy use for fine tuning an existing model
from a config file.

If `vocab` is given, we will extend the loaded model's vocabulary using the passed vocab
object (including calling `extend_embedder_vocab`, which extends embedding layers).
allennlp/models/model.py