[sharps_xp]

ESI, at least on fastly, are run in serialized fashion. On cloudflare workers, you can have up to 6 concurrent connections to try to do ESI as fast as the slowest request.

[pbowyer]

There's now a free Varnish VMOD to run ESI requests in parallel: https://code.uplex.de/uplex-varnish/libvdp-pesi