from transformers import SeamlessM4Tv2ForSpeechToSpeech
model = SeamlessM4Tv2ForSpeechToSpeech.from_pretrained("facebook/seamless-m4t-v2-large")

Or you can replace the text-to-text generation snippet with the model dedicated to the T2TT task, you only have to remove generate_speech=False.
thon

from transformers import SeamlessM4Tv2ForTextToText
model = SeamlessM4Tv2ForTextToText.from_pretrained("facebook/seamless-m4t-v2-large")