Cisco Systems This document extends Universally Unique Identifiers (UUIDs) beyond 128 bits to facilitate enhanced collision resistance and proper room for embedding additional data within a given UUID algorithm. These longer variable-length UUIDs ("UUID Long") leverage a previously unused variant bit "F" and feature a new sub-typing mechanism created to ensure there is enough space to define many future UUID algorithms within this new variant of UUIDs. This document updates RFC9562.