`google-cloud-texttospeech: SynthesizeLongAudioRequest` fails when using Gemini `gemini-2.5-pro-tts` model

[Aananda-giri]

I am attempting to use the gemini-2.5-pro-tts model, voice: Puck with the Long Audio Synthesis API for generating long-form audio.

I am following the official documentation for creating long-form audio:
https://docs.cloud.google.com/text-to-speech/docs/create-audio-text-long-audio-synthesis

Given code snippet works correctly. But, when passing gemini-2.5-pro-tts as model_name, and Puck as name, it is giving error: This voice requires a model name to be specified.

Code causing the error:

voice = texttospeech.VoiceSelectionParams(
    language_code="en-US",
    name="Puck",
    model_name="gemini-2.5-pro-tts" # This line seems to cause the Long Audio API to fail
)
client.synthesize_long_audio(request=request)

# full code:  https://docs.cloud.google.com/text-to-speech/docs/create-audio-text-long-audio-synthesis#create_audio_data

Observed Error:

InvalidArgument: 400 This voice requires a model name to be specified.

[Hellio404]

I have the same issue using the api directly, it looks like the modelName is ignored but also required on the long audio synthesis api