The gPTP message priority is defined in IEEE Std 802.1AS2020, 8.4.4.

It is recommended that gPTP messages are transmitted using the traffic class associated with Network Control as defined in Table 1 and derived from 6.4.3.

NOTE IEEE Std 802.1AS2020 defines gPTP messages to be transmitted untagged, i.e., frames do not carry priority information for traffic class selection. At the same time, IEEE Std 802.1AS2020 neither specifies a well-defined device-internal priority nor management capabilities for the configuration of the traffic class to be used for the transmission of gPTP messages.