A2A — Agent-to-Agent protocol in Joule

What it is

Agent2Agent (A2A) is an open protocol that lets one autonomous agent discover another agent, delegate a task to it and follow that task to completion, without either side exposing its internal prompts, tools or data. Google introduced it in April 2025; on 23 June 2025 the Linux Foundation launched the A2A project with Google, AWS, Cisco, Microsoft, Salesforce, SAP and ServiceNow as named founding contributors. The specification reached version 1.0, its first stable release, in early 2026; the Linux Foundation reported more than 150 supporting organisations at the protocol's first anniversary in April 2026, with support in Microsoft Azure AI Foundry, Copilot Studio and Amazon Bedrock AgentCore.

A2A is complementary to MCP: MCP is how an agent uses tools and data, A2A is how it works with another agent (see C132 for the hop-by-hop rule).

Why it matters

• SAP is a named founding contributor of the Linux Foundation A2A project (June 2025), and Joule's bi-directional A2A was announced as GA for Q4 2026 — cross-vendor agent collaboration is now on SAP's product roadmap, not only in standards bodies.
• A2A 1.0 fixed the details that earlier material gets wrong: Agent Card at /.well-known/agent-card.json, eight task states, three standard bindings, signed Agent Cards.
• Governance is split: SAP AI Agent Hub inventories and verifies agents and MCP servers, while runtime trust relies on identity and signed cards — there is no 'Joule Agent Hub' gateway.

Key points

• A2A: open agent-to-agent protocol introduced by Google in April 2025; Linux Foundation project since 23 June 2025 with SAP among the founding contributors.
• Version 1.0 is the first stable specification (early 2026): signed Agent Cards, multi-protocol bindings, multi-tenancy.
• Agent Card discovery at https://{domain}/.well-known/agent-card.json, or via registry or direct configuration.
• Task states: submitted, working, input-required, auth-required, completed, failed, canceled, rejected; updates via polling, streaming or push notifications.
• Joule Studio agents natively support A2A; Joule's bi-directional A2A announced GA in Q4 2026 (Sapphire 2026).
• Pro-code: CAP @cap-js/agents serves CAP services as A2A agents; SAP blogs show them surfaced in Joule via the Joule Studio CLI.
• Governance: SAP AI Agent Hub (SAP LeanIX) for inventory and verification; SAP API Policy §2.2.2 for agentic API use.

Terms used on this page

A2A (Agent2Agent protocol)

Open protocol, governed by a Linux Foundation project, for agents on different platforms to discover each other and delegate tasks without exposing internals.

Agent Card

JSON document describing an agent's identity, skills, endpoints, bindings and security schemes, published at /.well-known/agent-card.json or in a registry; may be signed.

Task

Stateful unit of delegated work in A2A, moving through states such as working, input-required, completed or rejected.

Push notification

A2A update mechanism in which the server agent calls a webhook registered by the client, used for long-running tasks.

Signed Agent Card

Agent Card carrying a signature over a canonicalised form, letting a caller verify its authenticity (A2A 1.0).

SAP AI Agent Hub

SAP LeanIX-based command center that discovers and governs AI agents, LLMs and MCP servers across SAP and non-SAP platforms.

Sources

1. A2A Protocol — Specification (version 1.0)
2. A2A Protocol — Agent Discovery
3. Linux Foundation — Launch of the Agent2Agent Protocol Project (23 Jun 2025)
4. Linux Foundation — A2A surpasses 150 organizations (9 Apr 2026)
5. SAP News — New agentic capabilities on SAP BTP (TechEd, Nov 2025)
6. SAP News — The Future of the Enterprise Is Autonomous (Sapphire, May 2026)
7. SAP News — Announcing New Joule Studio (May 2026)
8. SAP Community — Integrate a Pro-Code CAP A2A Agent with Joule (Aug 2026)
9. SAP Help — SAP AI Agent Hub
10. SAP News — Autonomous enterprise: business transformation management solutions and SAP AI agents at work at scale (SAP AI Agent Hub, 2026-09)
11. A2A Protocol — Life of a Task topic (task states and lifecycle detail)
12. SAP Community — Joule A2A: connect code-based agents into Joule (SAP-authored)