I am not sure if varnish-4 would be enough or also should try with varnish-3 (as maybe 4.x versions won't be ready to be stabilized in the near future) Thanks
~/cvsPortage/gentoo-x86/www-servers/varnish $ sudo PYTHON_TARGETS=python3_4 ebuild varnish-4.0.3.ebuild clean install * Removing unnecessary /usr/lib64/varnish/libvarnishcompat.la (no static archive) * Removing unnecessary /usr/lib64/varnish/libvarnish.la (no static archive) * Removing unnecessary /usr/lib64/varnish/libvcc.la (no static archive) * Removing unnecessary /usr/lib64/varnish/libvgz.la (no static archive) * Removing unnecessary /usr/lib64/libvarnishapi.la (no static archive) >>> Completed installing varnish-4.0.3 into /mnt/gen2/TmpDir/portage/www-servers/varnish-4.0.3/image/ *varnish-4.0.3 (19 Feb 2015) 19 Feb 2015; Anthony G. Basile <blueness@gentoo.org> +varnish-4.0.3.ebuild: is already ready. 03 Apr 2015; Ian Delaney <idella4@gentoo.org> varnish-4.0.3.ebuild: Clean old impls, add py3.4 support