Is it possible to reduce a raster to hold just 1 or 0 values with gdal? I find no data formats less than "Byte" in the documention
GeoTIFF with NBITS=1 is binary even the datatype is Byte https://gdal.org/drivers/raster/gtiff.html. I do not know the internal structure of such TIFF but together with the CCITT Group 4 compression that is designed long time ago for fax machines it yields very small file size.
gdal_translate -of GTiff -co NBITS=1 -co compress=CCITTFAX4 input.tif output.tif