def _find_response_start_index(tokens):
  r"""Finds the start of the response in the prompt.

  Args:
    tokens: A list of strings.

  Returns:
    The index of the last occurrence of '<start_of_turn>' followed by 'model'
    and '\n', or 1 if the sequence is not found. This corresponds to the start 
    of the response.
  """
  assert len(tokens) >= 3, "Response doesn't match expectation."
  for i in range(len(tokens) - 3, -1, -1):
    if (
        tokens[i] == '<start_of_turn>'
        and tokens[i + 1] == 'model'
        and tokens[i + 2] == '\n'
    ):
      return i + 3  # Return the index after the sequence
  raise ValueError("Response doesn't match expectation.")
Finds the start of the response in the prompt.

  Args:
    tokens: A list of strings.

  Returns:
    The index of the last occurrence of '<start_of_turn>' followed by 'model'
    and '\n', or 1 if the sequence is not found. This corresponds to the start 
    of the response.
  
concordia/language_model/together_ai.py