There are three types of OS10 architectures, Layer 2, Layer 3, and hybrid (Layer 2 & 3).
The first diagram shows a Layer 3 EVPN BGP-based architecture. Here the fabric consists of Layer 3 connections with an overlay enabling Layer 2 domain stretch across an IP or Layer 3 environment.
The second diagram shows a Layer 2 based architecture where the entire fabric is a Layer 2 construct for this deployment.
This architecture is a simple leaf and spine Layer 2 fabric handing off Layer 2 traffic to the data center interconnect (DCI) cloud.
The Edge leaf pair switches do not connect with any workloads, they provide critical inter-site communication handing off local site traffic to the DCI cloud. The workload leaf pairs (see switches in orange rectangle) provide east to west intra-cluster communication.