Live Protocol Comparison · Updated After Shoptalk Spring 2026
Agentic Commerce Protocol Tracker
Eight protocols are defining how AI agents discover, transact, pay, and communicate in the emerging agentic economy. This tracker compares their capabilities, trust architecture, and design implications through the lens of Agentic Experience Design. Updated with announcements from Shoptalk Spring 2026.
Shoptalk Spring 2026 Updates
Shoptalk Spring 2026 (24-26 March, Las Vegas) was the week agentic commerce became operational. Six companies made structural commitments that moved autonomous AI shopping from keynote speculation to production infrastructure. See the full analysis in Observatory Issue 065.
Multi-item carts, loyalty linking, Google Pay integration. Zero fees, open standard. Gap joins as first fashion brand partner.
OpenAI
ACPInstant Checkout abandoned. Pivoted to discovery-first architecture. Real-time product data from Target, Sephora, Nordstrom, Home Depot, Best Buy, Wayfair.
Stripe
MPPMachine Payments Protocol formally launched. Shared Payment Tokens for delegated spending authority. Purpose-built for machine-to-machine payments.
Mastercard
VI / Agent PayLive agentic payment transactions across Latin America. Tokenised credentials with biometric verification. First production-scale agentic payment network.
Shopify
UCP PartnerAgentic Storefronts activated by default for every merchant. Discoverable in ChatGPT, Copilot, Google AI Mode, Gemini. No additional fees.
Walmart
Multi-ProtocolSparky AI assistant deployed inside ChatGPT and Gemini. Bridges AI discovery to branded, personalised Walmart experience.
The Agentic Protocol Stack
No single protocol covers the full agentic commerce stack. The eight protocols tracked here operate at three distinct layers - infrastructure (how agents connect to tools and each other), commerce (how agents discover and purchase), and payment and identity (how agents prove authorisation and execute transactions). Understanding which layer each protocol addresses is essential for trust architecture design.
Commerce Layer
Product discovery, multi-item cart, checkout, fulfilment
Payment & Identity Layer
Authorisation, verification, payment execution
Infrastructure Layer
Agent-to-tool and agent-to-agent communication
UCP - Universal Commerce Protocol
Google & Shopify · Launched January 2026 (NRF 2026)
Shoptalk 2026 Update
Multi-item carts, loyalty linking, and Google Pay integration
At Shoptalk Spring 2026, Google expanded UCP with cross-retailer multi-item carts, loyalty rewards linking, and checkout via Google Pay with saved payment information. The coalition now includes Shopify, Walmart, Target, Etsy, Wayfair, and Gap, with endorsements from Mastercard, Visa, Stripe, and American Express. Google charges no additional fees and retailers remain the seller of record. Gap became the first major fashion brand to partner with Google for agent-driven commerce within Gemini.
Scope
Full commerce lifecycle: discovery, multi-item cart, checkout via Google Pay, loyalty linking, fulfilment, returns
Core Technology
Modular capabilities under dev.ucp.* namespace; JSON-LD, Schema.org; Google Pay integration
Primary Focus
Merchant-agent interoperability across the entire shopping journey
Trust Anchor
Credential providers and merchant-verified product feeds
Key Standards
JSON-LD, Schema.org, Agent Payments Protocol (AP2)
Last Updated
March 2026 (Shoptalk)
Key Partners
AXD Analysis
UCP is the most comprehensive commerce protocol from an AXD perspective. Its modular architecture maps to the trust architecture principle of layered capability - agents gain access to capabilities (Cart, Catalog, Identity Linking) incrementally, which mirrors the AXD concept of graduated delegation. The Shoptalk 2026 expansion to multi-item carts and loyalty linking deepens this graduated model. The Identity Linking capability is particularly significant: it addresses the machine customer identity problem that AXD identifies as foundational to agentic commerce. Google's zero-fee, open-governance approach gives UCP a structural advantage in merchant adoption.
Related Observatory Essays
ACP - Agentic Commerce Protocol
OpenAI & Stripe · Launched Late 2025 (Apache 2.0)
Shoptalk 2026 Update
Instant Checkout abandoned; pivoted to discovery-first architecture
At Shoptalk Spring 2026, OpenAI quietly retired its Instant Checkout feature, moving purchases to apps where they can happen more seamlessly. The revised ACP now focuses on real-time product data delivery from Target, Sephora, Nordstrom, Home Depot, Best Buy, and Wayfair directly into ChatGPT. Sephora launched a dedicated ChatGPT app for beauty shopping. The pivot confirms the consumer trust ceiling: only 10% of consumers make purchases on native AI chatbots (EMARKETER). Discovery is trusted; autonomous checkout is not.
Scope
Discovery-first: real-time product data delivery and agent-assisted shopping within ChatGPT
Core Technology
Stripe Shared Payment Token; real-time product feeds; app-based checkout
Primary Focus
AI-powered product discovery and recommendation within the ChatGPT ecosystem
Trust Anchor
Stripe as payment processor; retailer as seller of record (post-pivot)
Key Standards
Apache 2.0, Stripe API, OpenAI plugin architecture
Last Updated
March 2026 (Shoptalk)
Key Partners
AXD Analysis
ACP's pivot from Instant Checkout to discovery-first architecture at Shoptalk 2026 is the defining case study for the consumer trust ceiling thesis. OpenAI's official statement was measured: 'Instant Checkout is moving to Apps, where purchases can happen more seamlessly.' The translation is more direct: completing a transaction inside a chat interface does not work reliably enough at scale. This confirms the AXD principle that trust must precede transaction. The revised ACP now delivers real-time product data from Target, Sephora, Nordstrom, Home Depot, Best Buy, and Wayfair, focusing on discovery rather than checkout. OpenAI charges a 4% transaction fee on checkout transactions.
Related Observatory Essays
Visa TAP - Trusted Agent Protocol
Visa · Launched 2025
Scope
Agent identity verification and bot mitigation at the merchant edge
Core Technology
RFC 9421 (HTTP Signatures); Agent Recognition Header
Primary Focus
Interaction trust - enabling merchants to recognise and verify approved agents
Trust Anchor
Web-layer program participation; public key registries
Key Standards
IETF RFC 9421, OpenID, EMVCo
Last Updated
March 2026 (Shoptalk)
Key Partners
AXD Analysis
Visa TAP addresses the agent identity layer that AXD identifies as essential for trust architecture. The 8-minute operational window is a delegation design constraint - it limits the temporal scope of agent authority. The Linked Consumer Identity Object maps directly to the AXD concept of principal-agent binding. TAP's focus on 'interaction trust' (merchant-side verification) complements Mastercard VI's focus on 'authorisation trust' (issuer-side verification). At Shoptalk 2026, Visa announced agentic-ready credentials as part of the broader payment infrastructure buildout.
Related Observatory Essays
Mastercard VI - Verifiable Intent
Mastercard · Launched 2025
Shoptalk 2026 Update
Live agentic payment transactions in Latin America
At Shoptalk Spring 2026, Mastercard announced it had completed live agentic payment transactions across Latin America and the Caribbean using tokenised credentials and biometric verification. These are production transactions processed through the existing Mastercard network, with real money moving between real accounts, authorised by AI agents operating within delegated spending parameters. This represents the first production-scale deployment of constrained autonomous spending authority - delegation design implemented at the network level.
Scope
Cryptographic proof of human authorisation for agent transactions; live production payments
Core Technology
SD-JWT (Selective Disclosure JSON Web Token); 3-layer credential model; tokenised credentials; biometric verification
Primary Focus
Authorisation and auditability - proving the human intended the agent to act
Trust Anchor
Financial institution (issuer) as root of trust
Key Standards
FIDO, EMVCo, IETF, W3C
Last Updated
March 2026 (Shoptalk)
Key Partners
AXD Analysis
Mastercard VI is the most architecturally sophisticated protocol from an AXD perspective. Its 3-layer SD-JWT model (issuer identity, user intent, agent fulfilment) maps precisely to the AXD delegation chain: principal, mandate, agent action. The 8 registered constraint types are machine-readable delegation boundaries - exactly what AXD calls 'structured delegation'. VI's selective disclosure model addresses the privacy dimension of trust architecture that most other protocols ignore. At Shoptalk 2026, Mastercard moved from specification to production, completing live agentic payment transactions across Latin America and the Caribbean - the first production-scale agentic payment network.
Related Observatory Essays
MPP - Machine Payments Protocol
Stripe & Tempo · Launched March 2026 (Shoptalk)
Shoptalk 2026 Update
Machine Payments Protocol formally launched
At Shoptalk Spring 2026, Stripe formally launched the Machine Payments Protocol - purpose-built payment infrastructure for AI agents. The key innovation is the Shared Payment Token, a delegated credential that allows an AI agent to spend within predefined parameters without requiring human authorisation at the point of transaction. MPP is designed for agent-to-merchant transactions and works alongside Visa's card specifications. This positions Stripe as the protocol-level payment solution, complementing Mastercard's network-level approach.
Scope
Purpose-built payment infrastructure for AI agent-to-merchant transactions
Core Technology
Shared Payment Tokens; delegated spending authority; tokenised card payments; agent-specific payment credentials
Primary Focus
Enabling trusted agents to execute payments within predefined parameters without human intervention at checkout
Trust Anchor
Card network trust infrastructure; Visa card spec and SDK; Shared Payment Token constraints
Key Standards
EMVCo, Visa card specifications
Last Updated
March 2026 (Shoptalk)
Key Partners
AXD Analysis
MPP represents the payment execution layer of agentic commerce - the moment delegation becomes transaction. Formally launched at Shoptalk Spring 2026, MPP's key innovation is the Shared Payment Token - a delegated credential that allows an AI agent to spend within predefined parameters without requiring human authorisation at the point of transaction. This is delegation design implemented at the payment layer: the human sets the boundaries, the agent operates within them, and the payment infrastructure enforces the constraints. From an AXD perspective, MPP creates a new class of payment actor: the machine customer with its own payment credentials. Where Mastercard extended its existing network to support agent-initiated transactions, Stripe built a purpose-designed protocol for machine-to-machine payments.
Related Observatory Essays
MCP - Model Context Protocol
Anthropic, Linux Foundation · Launched November 2024
Scope
Standardised interface between LLM-based agents and external tools/APIs
Core Technology
JSON-RPC 2.0 over HTTP; SSE for streaming; tools/resources/prompts primitives
Primary Focus
Agent-to-tool communication - the 'USB-C for AI'
Trust Anchor
Host application as trust boundary; server-side capability declarations
Key Standards
JSON-RPC 2.0, HTTP, SSE
Last Updated
March 2026
Key Partners
AXD Analysis
MCP is the foundational infrastructure protocol that enables agent capability. From an AXD perspective, MCP's tool/resource/prompt primitives define the agent's operational surface - what the agent can do. This makes MCP the technical substrate for delegation design: the tools available via MCP determine the scope of authority that can be delegated. MCP's trust boundary model (host app as gatekeeper) is an implementation of the trust architecture principle.
Related Observatory Essays
A2A - Agent-to-Agent Protocol
Google, Linux Foundation · Launched April 2025
Scope
Cross-framework agent-to-agent communication and task delegation
Core Technology
JSON-over-HTTP; JSON-RPC 2.0; SSE and webhooks; Agent Cards
Primary Focus
Multi-agent orchestration - enabling agents to collaborate across vendors
Trust Anchor
Agent Cards (standardised metadata); task lifecycle state management
Key Standards
JSON-RPC 2.0, HTTP, SSE, Webhooks
Last Updated
March 2026
Key Partners
AXD Analysis
A2A's task lifecycle (submitted, working, completed) maps directly to AXD's delegation lifecycle. Agent Cards - standardised metadata that describes an agent's capabilities - are the technical implementation of what AXD calls 'agent legibility'. A2A enables the multi-agent orchestration patterns described in Framework 06, where multiple agents collaborate on complex tasks with different trust levels and delegation scopes.
Related Observatory Essays
ACP (IBM) - Agent Communication Protocol
IBM Research / BeeAI, Linux Foundation · Launched March 2025
Scope
Framework-agnostic agent interoperability with multimodal content exchange
Core Technology
REST APIs; built-in agent registration and discovery
Primary Focus
Rich content exchange between agents regardless of underlying framework
Trust Anchor
Agent registration system; capability-based discovery
Key Standards
REST, HTTP, JSON
Last Updated
March 2026
Key Partners
AXD Analysis
IBM's ACP emphasises content richness and framework agnosticism - principles that align with AXD's argument that agent communication must carry trust metadata alongside functional data. The protocol's agent registration system is an early implementation of the agent identity infrastructure that AXD identifies as essential for trust architecture at scale.
Related Observatory Essays
Payment Protocol Comparison
Visa TAP, Mastercard VI, and Stripe MPP represent three complementary approaches to the trust problem in agentic payments. TAP verifies the agent at the merchant edge; VI proves the human's intent at the issuer level; MPP provides the delegated payment credential. Together, they form the emerging trust infrastructure for agentic commerce. After Shoptalk 2026, the payment layer of the agentic stack is now operational.
| Feature | Visa TAP | Mastercard VI | MPP |
|---|---|---|---|
| Core Technology | RFC 9421 (HTTP Signatures) | SD-JWT (Layered Credential) | Shared Payment Tokens |
| Primary Verifier | Merchants / Edge Protection | Issuers / Networks / Wallets | Card networks / Stripe |
| Verification Focus | Interaction & Bot Mitigation | Authorisation & Auditability | Delegated spending authority |
| Key Standards | IETF, OpenID, EMVCo | FIDO, EMVCo, IETF, W3C | EMVCo, Visa specs |
| Execution Mode | Real-time (8-min window) | Immediate or Autonomous | Agent-initiated, predefined parameters |
| Privacy Model | Payload partitioning | Selective disclosure (SD-JWT) | Card tokenisation |
| AXD Trust Layer | Interaction trust | Authorisation trust | Transaction trust |
| Shoptalk 2026 | Agentic-ready credentials | Live production in Latin America | Formal protocol launch |
Source: Fintech Wrap Up, Visa Perspectives, Mastercard, Stripe, Techstrong AI. Updated March 2026 (Shoptalk).
Commerce Protocol Comparison
UCP and ACP represent two architecturally distinct approaches to agentic shopping. After Shoptalk 2026, the divergence is sharper: UCP expanded into multi-item carts and loyalty linking while ACP pivoted from checkout to discovery. Both require merchant opt-in, which is why the coverage gap remains the central challenge. See The Consumer Trust Ceiling for the AXD analysis.
| Feature | UCP | ACP |
|---|---|---|
| Developers | Google & Shopify | OpenAI & Stripe |
| Governance | Open standard, multi-stakeholder | Proprietary, OpenAI-controlled |
| Transaction Fees | None | 4% on checkout transactions |
| Scope | Full lifecycle (discovery, cart, checkout, returns) | Discovery-first (post-Shoptalk pivot) |
| Payment Model | Multiple handlers (AP2), Google Pay | Stripe Shared Payment Token |
| Platform Reach | Surface-agnostic (AI Mode, Gemini, etc.) | ChatGPT ecosystem |
| Multi-Item Cart | Yes, cross-retailer (Shoptalk 2026) | Single retailer |
| Loyalty Integration | Yes, rewards linking (Shoptalk 2026) | Not announced |
| Checkout Model | Redirect to retailer with Google Pay | Redirect to retailer (Instant Checkout deprecated) |
| Coalition Size | 25+ companies (Shopify, Walmart, Target, etc.) | 10+ companies (Target, Sephora, Nordstrom, etc.) |
| AXD Assessment | Graduated delegation model | Consumer trust ceiling case study |
Source: Google Developers, OpenAI, Rye.com, Ecommerce Fastlane, EMARKETER. Updated March 2026 (Shoptalk).
Frequently Asked Questions
What is the difference between UCP and ACP in agentic commerce?
UCP (Universal Commerce Protocol) and ACP (Agentic Commerce Protocol) are both standards for AI agent shopping, but they differ fundamentally in scope, governance, and architecture. UCP, developed by Google and Shopify, covers the full commerce lifecycle - discovery, multi-item cart, checkout via Google Pay, loyalty linking, fulfilment, and returns - using a modular capability system. It is an open standard with no transaction fees. ACP, developed by OpenAI and Stripe, initially focused on checkout but pivoted at Shoptalk 2026 to discovery-first architecture after retiring Instant Checkout. OpenAI charges a 4% transaction fee. UCP is surface-agnostic (works across Google AI Mode, Gemini, and other platforms), while ACP primarily powers the ChatGPT ecosystem. Both require merchant opt-in, which is why the coverage gap remains the central challenge in agentic commerce.
How do Visa TAP and Mastercard Verifiable Intent compare?
Visa's Trusted Agent Protocol (TAP) and Mastercard's Verifiable Intent (VI) address different layers of the trust problem in agentic payments. TAP focuses on interaction trust - enabling merchants to recognise and verify approved AI agents at the web edge using HTTP Signatures (RFC 9421). VI focuses on authorisation trust - providing cryptographic proof that a human intended the agent to act, using a 3-layer SD-JWT credential model. TAP's primary verifier is the merchant; VI's primary verifier is the issuing financial institution. They are complementary rather than competing: TAP answers 'is this agent legitimate?' while VI answers 'did the human authorise this action?'
What is MCP and how does it relate to agentic commerce?
MCP (Model Context Protocol), created by Anthropic and now governed by the Linux Foundation, standardises how AI agents connect to external tools and APIs. While not a commerce protocol itself, MCP is the foundational infrastructure layer that enables agents to access commerce capabilities. An AI shopping agent might use MCP to connect to product databases, payment processors, and merchant APIs. MCP defines what an agent can do; commerce protocols like UCP and ACP define how it shops and transacts.
Why are there so many competing protocols for agentic commerce?
The proliferation of protocols reflects the multi-layered nature of agentic commerce. No single protocol can address all requirements: agent-to-tool communication (MCP), agent-to-agent coordination (A2A), product discovery and checkout (UCP/ACP), payment authorisation (Visa TAP, Mastercard VI), and payment execution (MPP). Each protocol addresses a specific layer of the stack. The AXD Institute tracks these protocols because their design decisions - particularly around trust, delegation, and identity - determine the trust architecture of the emerging agentic economy.
Which protocol should organisations adopt first?
The answer depends on the organisation's role in the agentic commerce ecosystem. Merchants should prioritise UCP (for product discovery and checkout interoperability) and Visa TAP (for agent verification at the edge). Payment providers should implement MPP and Mastercard VI. Agent developers should adopt MCP (for tool access) and A2A (for multi-agent coordination). All organisations should monitor ACP's evolution as OpenAI's ecosystem remains significant despite the Instant Checkout pivot. The AXD Institute recommends starting with the protocol that addresses your most immediate trust architecture gap.
What changed at Shoptalk 2026 for agentic commerce protocols?
Shoptalk Spring 2026 (24-26 March, Las Vegas) was the week agentic commerce became operational. Google expanded UCP with multi-item carts, loyalty linking, and Google Pay integration. OpenAI abandoned Instant Checkout and pivoted ACP to discovery-first architecture. Stripe formally launched the Machine Payments Protocol with Shared Payment Tokens for delegated spending authority. Mastercard completed live agentic payment transactions across Latin America using tokenised credentials and biometric verification - the first production-scale agentic payment network. Shopify activated Agentic Storefronts by default for every merchant. Walmart deployed its Sparky AI assistant inside ChatGPT and Gemini. The payment layer of the agentic commerce stack is now operational.
What is Stripe's Machine Payments Protocol?
Stripe's Machine Payments Protocol (MPP), formally launched at Shoptalk Spring 2026, is purpose-built payment infrastructure for AI agents. The key innovation is the Shared Payment Token - a delegated credential that allows an AI agent to spend within predefined parameters without requiring human authorisation at the point of transaction. MPP works alongside Visa's card specifications and is designed for agent-to-merchant transactions. Where Mastercard extended its existing network to support agent-initiated transactions, Stripe built a purpose-designed protocol for machine-to-machine payments. MPP represents delegation design implemented at the payment layer: the human sets the boundaries, the agent operates within them, and the payment infrastructure enforces the constraints.
Assess Your Protocol Readiness
Is Your Organisation Ready for Agentic Commerce?
The protocol landscape is evolving rapidly. After Shoptalk 2026, the payment layer is operational and the commerce layer is splitting between open and proprietary standards. The AXD Readiness Assessment evaluates your organisation's preparedness across trust architecture, delegation design, agent observability, and recovery design.