Segment routing is the evolution of the MPLS. Segment routing is label switching but without a protocol. It is adding extensions to the IGP.
In Segment routing, each router has nodal ID and each segment/link has a segment ID.
Packet is being forwarded based on predefined path which contains all the way to the destination so some routers in the middle of the path don't need to do any kind of lookup they just forward the traffic to the nodal ID.