An interface for coupling an agent to a fabric supports a load/store interconnect protocol, where the I/O interconnect protocol includes a flit mode and a non-flit mode. A set of flit mode header formats are used when in the flit mode and a set of non-flit mode header formats are used when in the non-flit mode, the set of non-flit mode header formats including one or more non-flit mode fields. Interface logic determines that a link is trained to the non-flit mode and generates a header according to the set of flit mode header formats, where the header includes a field to indicate that a corresponding packet originated as a non-flit mode packet. One or more fields of the set of flit mode header formats are repurposed in the header to carry the one or more non-flit mode fields before sending the modified header over the interface.