Brotli, another one of those pseudostandards[1] from Big G that I was avoiding all along. Dodged another bullet.

[1] When more than half of the "standard" https://www.rfc-editor.org/info/rfc7932/#page-44 is an opaque binary blob, they're really not encouraging independent implementations.

Edit: the votes really show what an echochamber for Big G this place has become. FUCK YOU, GOOGLE!