Thanks for that direct FTP link...
I am looking for the equivalent of http://hgdownload.cse.ucsc.edu/goldenPath/hg19/database/gc5Base.txt.gz but in hg38. Any idea how can I convert this .bw (bigwig?) format into an identical format to the above link?
(Trying to perform CNV calling using pennCNV but with the hg38 genomebuild.)

Yes I know, but with this option, the output file can only have 100,000 lines. I am interested in the whole genome. The same page says that 'the entire dataset may be available on downloads page'. But this page has gc%data only for hg19.
May be this file is not available at all for hg38 yet?