I assume this is do to egress from S3. I wonder how that cost compares to re-generating the historic caches. Presumably that is possible with nix. One issue th

I assume this is do to egress from S3. I wonder how that cost compares to re-generating the historic caches. Presumably that is possible with nix. One issue that you'll run into is that many upstream source archives are not available anymore at the original URL. Though I think it should be possible to collect all fixed-output derivations and copy their outputs over to a new cache and then try to build. Once these are in the cache, Nix will not try to download the sources from the original location but use the binary cache instead.