src/transformers/tokenization_utils_base.py/PreTrainedTokenizerBase/max_len_sentences_pair
class PreTrainedTokenizerBase:    def max_len_sentences_pair(self) -> int:
        """
        :obj:`int`: The maximum combined length of a pair of sentences that can be fed to the model.
        """
        return self.model_max_length - self.num_special_tokens_to_add(pair=True)