Configuring Group Size for BitsAndBytesConfig

I am trying to find a way to configure the group size (a.k.a. block size) of NF4 quantization.
According to my understanding, NF4 quantization can be done by BitsAndBytesConfig.

Looking at this documentation page:

Some configs like AwqConfig and GPTQConfig do have group_size arg but `BitsAndBytesConfig| doesn’t.

How can I know what is the group_size of BitsAndBytesConfig and how can I modify it?