3GPP 24.501 v20.0.0 — the document's own text
6.2.4.2a IPv6 prefix delegation via DHCPv6
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
In order to perform the IPv6 prefix delegation via DHCPv6, the UE shall use DHCPv6 to request additional IPv6 prefixes (i.e. prefixes shorter than the default /64 prefix) from the SMF. The UE shall act as a "Requesting Router" as described in IETF RFC 9915 [33D] and shall insert one or more identity association for prefix delegation options into a DHCPv6 Solicit message.
If the IPv6 address allocation using IPv6 stateless address autoconfiguration is used, the UE sends the DHCPv6 message to request additional IPv6 prefixes to the SMF after the PDU session establishment and IPv6 prefix allocation.
When the UE requests additional prefixes using DHCPv6, the UE may include DHCPv6 Rapid Commit option as specified in IETF RFC 9915 [33D] in a DHCPv6 Solicit message, and the UE other than the ones specified in clause 6.2.4.3 shall include DHCPv6 OPTION_ORO option with the OPTION_PD_EXCLUDE option code as specified in IETF RFC 6603 [40A] in the DHCPv6 message.
Upon receiving one or more identity association for prefix delegation prefixes in a DHCPv6 Reply message, the UE is allowed to use the allocated additional prefixes after inter-system change from N1 mode to S1 mode or from S1 mode to N1 mode.