Nomotic, Inc. The Agent Transfer Protocol (AGTP) operates as a substrate beneath several adjacent layers: Agent Group Messaging Protocols (AGMPs) such as the Model Context Protocol (MCP), the Agent-to-Agent Protocol (A2A), and the Agent Communication Protocol (ACP); external identity providers (OAuth, OIDC, enterprise IdPs); and HTTP-based clients that interact with agents through translation gateways. This document specifies the composition profiles for each of these adjacent layers, defining normative mapping rules between the adjacent layer and AGTP. Three composition families are specified. The AGMP composition profile specifies how MCP, A2A, and ACP messages are carried over AGTP, with mapping rules for identity, authority scope, delegation, and session fields between the AGMP and AGTP layers. The External Identity Provider composition profile specifies how AGTP agent identity composes with externally-issued credentials, treating "which agent" and "on whose behalf" as orthogonal axes. The HTTP Gateway composition profile specifies the translation surface for accepting HTTP traffic into AGTP- served agents as a REST adoption ramp. Across all three families, AGTP headers take precedence over equivalent adjacent-layer fields for all infrastructure-level routing, enforcement, and audit operations. Agents gain transport- level governance, observability, and identity without modification to the adjacent layers.