# Protocol Compatibility Matrix

The first multi-protocol payment bridge for AI agent commerce

Trusteed supports 10 payment protocols: MCP, UCP, and SCP are in production; x402 and ACP are in sandbox; AP2 is experimental; Visa VIC, Mastercard MCAP, PayPal, and MPP are coming soon. MPP, from Stripe and Tempo Labs (IETF draft-httpauth-payment-01), extends x402 with native MCP/JSON-RPC transport. Plus AG-UI for real-time human-in-the-loop checkout and A2A for agent-to-agent communication. Merchants enable the protocols they need; agents pick the one they support. The Protocol Router handles detection, normalization, and settlement automatically.

## Protocol matrix

| Protocol | Origin | Version | Status | Inbound | Outbound | Settlement | Sandbox |
|---|---|---|---|---|---|---|---|
| ACP | OpenAI / Stripe | v1.0 | sandbox | yes | yes | Stripe | demo-store |
| AP2 | Google | v0.1 | experimental | yes | yes | Cart Mandate | demo-store |
| x402 | Coinbase / Cloudflare | v1.0 | sandbox | yes | yes | USDC on-chain (Base Sepolia testnet) | available |
| VIC | Visa | v1.0 | coming-soon | yes | yes | Visa tokenization | available |
| KYApay | Skyfire | v1.0 | experimental | yes | yes | Skyfire | experimental |
| PayPal | PayPal | v1.0 | coming-soon | yes | yes | PayPal Commerce | available |
| MCAP | Mastercard | v1.0 | coming-soon | yes | no | Stripe (pass-through) | available |
| UCP | Trusteed | 2026-08-25 | active | yes | yes | Protocol Bridge | demo-store |
| AG-UI | Trusteed | v1.0 | production-ready | yes | no | Real-time confirmation | demo-store |

## Protocol details

### ACP — Agent Commerce Protocol

Fiat payments via Stripe. The standard for OpenAI-compatible agents.

- Detection: X-Protocol header or Stripe signature
- MCP tools: create_cart, complete_checkout, preview_checkout
- View spec: https://github.com/agentic-commerce-protocol/agentic-commerce-protocol

### AP2 — Agent Payment Protocol v2

Google's cart mandate model for agent purchases. Designed for Google-ecosystem agents.

- Detection: AP2 mandate headers
- MCP tools: create_cart, complete_checkout
- View spec: https://ap2-protocol.org/specification/

### x402 — x402 Stablecoin Protocol

USDC stablecoin payments via HTTP 402 for crypto-native agents. The rail is deployed and test transfers on the Base Sepolia testnet (no real value) are verified in the demonstration store, but no real merchant has a settleable configuration and there are no known settlements with real value.

- Detection: PAYMENT-SIGNATURE or X-PAYMENT header
- MCP tools: create_cart, complete_checkout
- View spec: https://www.x402.org/

### VIC — Visa Intelligent Commerce

Tokenized card payments using Visa Intelligent Commerce. 4-layer cryptography (JWE + X-Pay HMAC + MLE + HTTPS). 200+ tests. Awaiting Visa production credentials.

- Detection: VIC headers
- MCP tools: create_cart, complete_checkout
- View spec: https://developer.visa.com/

### KYApay — KYApay Identity-Linked Payments

Identity-linked JWT payments via Skyfire. Agent identity verification with payment execution. Enabled in production since 2026-09-05 with zero charges so far: no settlement over this rail can be claimed yet.

- Detection: KYApay JWT headers
- MCP tools: create_cart, complete_checkout
- View spec: https://skyfire.dev/

### PayPal — PayPal Commerce Platform

PayPal Orders API v2 for agent-initiated purchases. Buyer approval via elicitation URL. Refunds require merchant approval. 400M+ PayPal accounts worldwide (PayPal Q4 2024 earnings report).

- Detection: X-Protocol: PAYPAL header or paypal_order_id in body
- MCP tools: create_cart, complete_checkout
- View spec: https://developer.paypal.com/

### MCAP — Mastercard Agent Pay

Mastercard Agentic Token payments via Stripe pass-through. Ed25519 HTTP Message Signatures (RFC 9421). Verifiable Intent receipts. 78 tests. Zero-code for merchants with Stripe.

- Detection: Signature-Input header with tag=agent-payer-auth
- MCP tools: process_agent_payment, check_agent_consent
- View spec: https://developer.mastercard.com/

### UCP — Universal Commerce Protocol

Universal discovery and checkout abstraction across all protocols. One endpoint, any payment method.

- Detection: UCP discovery at /.well-known/ucp
- MCP tools: search_products, get_product_details, get_merchant_profile
- View spec: /.well-known/ucp

### AG-UI — Agent-User Interaction Protocol

Real-time human-in-the-loop checkout via Server-Sent Events. Cryptographic token confirmation, state synchronization via RFC 6902 JSON Patch, and tool call verification.

- Detection: Content-Type: text/event-stream + SSE stream
- MCP tools: ag_ui_stream, ag_ui_confirm
- View spec: /specs/024-ag-ui-protocol/spec.md

## Why multi-protocol?

- **Agent choice** — Agents pick the protocol they support. No negotiation, no fallback errors.
- **Revenue maximization** — Do not lose sales because an agent only speaks x402 and your store only speaks ACP.
- **Future-proof** — New protocols are added via the Plugin Registry. Your integration stays the same.
- **Single integration** — One MCP endpoint, all protocols. The Protocol Router handles detection and routing.

## Frequently asked questions

**Q: How many protocols can a merchant enable?**

A: All supported protocols simultaneously. MCP, UCP, and SCP are in production; ACP and x402 are in sandbox (the x402 rail is deployed and test transfers work in the demonstration store, but no real merchant has a settleable configuration, so no payment with real value completes over it today); AP2 is experimental; Visa VIC, Mastercard MCAP, and PayPal are coming soon. The Protocol Router selects the best match based on agent capabilities and merchant priority configuration.

**Q: Is there a cost per protocol?**

A: Protocol support is included in all tiers. Settlement fees would depend on the protocol provider: Stripe for ACP, the rail a merchant would settle through first. No rail moves money today: ACP is in sandbox and no merchant on the platform has a payment processor configured, so no charge can complete over any of them. Corrected 2026-09-05: this answer used to call ACP “the rail that actually moves money today”, contradicting both the FAQ above it and the signed capability registry. For x402 there is additionally nothing to charge for because no real merchant has a settleable configuration; the only settlements are test transfers on Base Sepolia in the demonstration store.

**Q: Can I add a custom protocol?**

A: Yes. The Plugin Registry supports custom adapters. Contact us for Enterprise integration support.

**Q: How does protocol detection work?**

A: The Protocol Detector middleware inspects request headers, signatures and body shape to identify the protocol. Each match carries a confidence value; an explicit `X-Protocol` header gives 1.0, and header- or signature-shape inference gives less. Below the detector's threshold no protocol is assumed and the request is handled as plain REST. No manual configuration is needed on the agent side.

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Canonical HTML version: https://trusteed.xyz/en/protocol-coverage