DHCPv4 requires explicit client configuration. You must set up the DHCPv4 system for addressing either during initial system installation or dynamically through the use of the ipadm command. See the ipadm(8) man page.
DHCPv6 does not require explicit client configuration. Instead, using DHCP is a property of the network. The signal to use DHCPv6 is carried in Router Advertisement messages from local routers. The dhcpagent daemon automatically creates and destroys logical interfaces as needed.
The DHCPv6 mechanism is very similar administratively to the existing IPv6 stateless (automatic) address configuration. For stateless address configuration, you would set a flag on the local router to indicate that, for a given set of prefixes, each DHCP client should automatically configure an address on its own by using the advertised prefix plus a local interface token or random number. For DHCPv6, the same prefixes are required but the addresses are acquired and managed through a DHCPv6 server instead of being assigned randomly.