bitsandbytes functional.py quantize_4bit (blocksize default and valid values)

Authoritative for the NF4/FP4 block size. Docstring verbatim: 'blocksize (int, optional): The size of the blocks. Defaults to 64. Valid values are 32, 64, 128, 256, 512, 1024, 2048, and 4096.' So 64 is a DEFAULT and a choice, not a format constant - the same NF4 checkpoint can be written at any of those sizes. bitsandbytes/nn/modules.py confirms Params4bit.__init__ does `if blocksize is None: blocksize = 64`. Accessed 2026-10-04.