tf.compat.v1.reduce_join

tf.compat.v1.reduce_join(
    inputs, axis=None, keep_dims=None, separator='', name=None,
    reduction_indices=None, keepdims=None
)

>>> tf.strings.reduce_join([['abc','123'],
...                         ['def','456']]).numpy()
b'abc123def456'
>>> tf.strings.reduce_join([['abc','123'],
...                         ['def','456']], axis=-1).numpy()
array([b'abc123', b'def456'], dtype=object)
>>> tf.strings.reduce_join([['abc','123'],
...                         ['def','456']],
...                        axis=-1,
...                        separator=" ").numpy()
array([b'abc 123', b'def 456'], dtype=object)