SentFI / eXpress402

eXpress402 The agent has a wallet with funds for doing research using paid MCPs. The problem we are solving is that an AI agent paying for an MCP behind x402 has to pay per transaction when it makes calls to the MCP tools to get data.

In x402 v2, there's a new extension called SIWx (Sign-In-With-X) that enables wallet-based authentication. By combining SIWx with Yellow Network's off-chain payment sessions, agents can authenticate once and pay once, then make unlimited subsequent calls without additional payments or per-transaction fees.

For per-call x402 v2 transactions without using a facilitator, we've implemented Arc + Circle Gateway for agentic unified USDC payments without the middleman.

Integrated Solutions LI.FI - Sentifi AI Trading Agent A fully autonomous sentiment-driven trading agent that demonstrates the power of prepaid MCP sessions:

Real-Time Market Intelligence: Queries market_rumors via our MCP + SIWx integration for Reddit discussions and news sentiment Intelligent Analysis: Negation detection, recency weighting, and engagement scoring to determine market sentiment

Autonomous Trading: Makes trading decisions and executes cross-chain swaps via LI.FI SDK across 30+ DEXs

Risk Management: Confidence-based position sizing, circuit breakers, and P&L tracking

Live Dashboard: Real-time visualization showing sentiment scores, trading decisions, and portfolio performance

Key Innovation: Sentifi pays once to establish a Yellow Network session, then makes unlimited market research queries without per-call blockchain fees - enabling high-frequency sentiment analysis that would be cost-prohibitive with traditional per-transaction payments.

We built Sentifi, an autonomous AI trading agent, to demonstrate the power of combining x402 payment protocol, Model Context Protocol (MCP), Yellow Network's app chain sessions, Arc + Circle Gateway direct USDC payments, and LI.FI cross-chain swaps. This is the first agent that can afford high-frequency market research by paying once and querying an arbitrary amount of times using Yellow rail in one on-chain transaction or making direct peer-to-peer USDC payments without intermediaries using Arc.

The Stack:

TypeScript, viem wallet Yellow's Nitrolite SDK for payment channels, Arc Testnet + Circle Gateway for direct USDC settlement, MCP for AI agent tool calls, Redis for session storage , and LI.FI SDK for cross-chain DEX aggregation. We implemented x402 v2 with CAIP-122 SIWx wallet authentication to enable autonomous agent payments. Application is deployed on Railway.

How Sentifi Works:

The agent needs real-time sentiment data to make trading decisions. When Sentifi makes its first MCP tool request (e.g., market_rumors), our server returns 402 Payment Required with a SIWx challenge. Sentifi signs a CAIP-122 message with its EOA wallet (proving identity), then chooses a payment rail:

Yellow Network Rail: Creates a Yellow Network app chain session with prepaid balance. Yellow's app chain sessions reduce the cost of fetching sentiment data to a single blockchain transaction and all subsequent queries are off-chain. We store wallet-sessionId mapping in Redis for sub-millisecond lookups. All operations use quorum 2 multi-sig governance to allow parties to vote in case of settlement disputes.

Arc + Circle Gateway Rail: Makes direct USDC payments per call via Circle Gateway on Arc Testnet. No intermediary takes fees so USDC goes directly from agent to merchant. The agent submits a gatewayMint transaction, our server verifies the on-chain AttestationUsed event proving payment, and returns the data. Perfect for scenarios requiring auditable, on-chain proof of each purchase.

Sentifi uses the same SIWx signature throughout the session lifecycle. The first request validates and store's the signature; subsequent requests recognize it and retrieve the associated session (Yellow) or verify the wallet identity (Arc). This design elegantly maps cryptographic identity to payment sessions without requiring new signatures for every call and is essential for autonomous operation.

Partner Technologies:

Yellow Network enables Sentifi to pay once for a session, then make hundreds of sentiment analysis queries off-chain. Their app chain sessions eliminate per-call gas fees while their quorum 2 governance ensures secure multi-party settlement when the session closes. We integrated their Nitrolite SDK and custody contracts for Base mainnet.

Arc + Circle Gateway provides direct USDC settlement on Arc Testnet with on-chain proof per purchase. No middleman fees—agents pay merchants directly using Circle's Gateway infrastructure. Perfect for use cases requiring verifiable payment trails and Arc-native USDC transactions.

LI.FI executes Sentifi's trading decisions across 30+ DEXs with optimal routing. After analyzing sentiment via prepaid queries, Sentifi swaps tokens cross-chain based on market signals, with LI.FI finding the best prices across multiple chains.