dhcpcd-4.0.0_beta1 out now. It has a big change - we no longer enable duid client id's by default. Instead, we have a new parameter
--duid, -D to enable it.
Gentoo users should look at bug #219321 for ebuilds. You should enable the compat USE flag if you want to retain commandline compatability with dhcpcd-3.x. This also re-enables duid by default IF the duid file exists.
dhcpcd-4 is now considered pretty much done. I was hoping to have some IPv6 in, but sadly not.