Today Cilium sets the cilium_host IPv6 addr to the same one as a native iface. The motivation for that is listed in the following commit message:

Some more context and background: for v6 (direct routing or tunnel
mode), the cilium_host device has a globally scoped v6 address which
matches the one of the public interface. This is due to the fact that
we cannot add a private address with link scope like in v4 case where
kernel can ensure that no traffic is leaked to the public:

However, recently we changed the scope of the cilium_host IPv4 addr from local to global - #23241, so the reasoning above probably should not be used as an argument.

Having the same IPv6 addr causes some issues when the L7 proxy is involved - #21954 (comment). Therefore, let's try to use the same IPAM allocation path for the IPv6 as we do today for the IPv4. The previous attempt to change that was in this non-merged PR - #16044.