[Scaevolus]

I'd expect it to still save >20%. Lepton uses arithmetic encoding instead of Huffman (-10%), and predicts each 8x8 block based on its neighbors (-20%). Guetzli shouldn't interfere with either of these.

[JyrkiAlakuijala]

When we pack guetzlified JPEGs we see slightly smaller wins than with stock JPEGs. Think -14% for guetzlified JPEGs vs. -20% libjpeg JPEGs.