Realtime API: Getting audio transcriptions even after turning off

API
1

I’m setting the session.update event as follows:

session_update = {
    "type": "session.update",
    "session": {
        "modalities": ["text", "audio"],
        "input_audio_transcription": None,
    },
}

Despite this, I get audio transcription in my responses. Response types logged below

input_audio_buffer.speech_stopped
conversation.item.created
rate_limits.updated
conversation.item.created
response.audio_transcript.delta delta = I’m
response.audio_transcript.delta delta = !
response.audio_transcript.delta delta = can
response.audio.delta
response.audio.delta
error
response.audio_transcript.delta delta = you
response.audio.delta
response.audio.delta
response.audio.done
response.content_part.done

Why is this happening? I want to turn off the audio transcriptions.