Fiat Rails: Bridging Traditional Banking to Agent Wallets

Most businesses run on dollars, not tokens. Fiat Rails is the Sardis design-partner lane for bank funding, card spend, and payout orchestration with policy enforcement. Stablecoins remain available as an optional settlement rail.

The Bridge Problem

Until now, funding an agent wallet required crypto fluency. Users needed to:

• Buy USDC on an exchange
• Transfer to the correct chain
• Bridge if necessary
• Fund the agent wallet

This friction blocks mainstream adoption. Enterprise finance teams do not want to manage crypto operations. They want to fund agents from existing banking workflows.

Fiat Rails in the current release

Fiat Rails uses provider integrations for settlement while Sardis enforces policy, idempotency, and auditability:

• Bank to Wallet: Fund agent workflows via ACH, wire, or card with quote-driven conversion when needed.
• Unified Balance: One policy budget can power crypto payments, virtual cards, and bank payouts.
• Wallet to Bank: Withdraw to USD with policy checks and compliance workflows.

The Flow

Here is how funds flow through the Sardis ecosystem:

Bank (ACH/Wire/Card) --> Treasury (USD account) --> Sardis Wallet (MPC + Policy) --> Card / Crypto / Bank

Avoiding unnecessary conversion cost

We use three operating modes to avoid forced double conversion:

1. Mode A: Fiat-first card treasury -- Keep a USD treasury for cards and only convert when crypto payout is requested.
2. Mode B: Stablecoin-first JIT -- Convert USDC to USD per spend when card usage is infrequent or highly variable.
3. Mode C: Hybrid threshold refill -- Maintain a USD buffer and top up in batches from stablecoins based on thresholds.

Implementation

We ship both Python and TypeScript SDKs for fiat operations.

Funding a Wallet

from sardis_sdk import AsyncSardisClient
from sardis_sdk.models.treasury import TreasuryPaymentRequest

async with AsyncSardisClient(api_key="sk_live_...") as client:
    payment = await client.treasury.fund(
        TreasuryPaymentRequest(
            financial_account_token="fa_issuing_123",
            external_bank_account_token="eba_123",
            amount_minor=500000,  # $5,000.00
            method="ACH_NEXT_DAY",
            sec_code="CCD",
            memo="Treasury top-up",
        )
    )

    print(payment.payment_token, payment.status)

Withdrawing to Bank

withdrawal = await client.treasury.withdraw(
    TreasuryPaymentRequest(
        financial_account_token="fa_issuing_123",
        external_bank_account_token="eba_123",
        amount_minor=250000,  # $2,500.00
        method="ACH_NEXT_DAY",
        sec_code="CCD",
        memo="Vendor payout",
    )
)

print(withdrawal.payment_token, withdrawal.status)

Paying Merchants Directly

// Pay a merchant in USD from crypto wallet
const payment = await ramp.payMerchantFiat({
  walletId: 'wallet_abc123',
  amountUsd: 499.99,
  merchant: {
    name: 'SaaS Provider Inc',
    category: 'software',
    bankAccount: {
      accountHolderName: 'SaaS Provider Inc',
      accountNumber: '...',
      routingNumber: '...'
    }
  }
})

// If policy requires approval:
// payment.status === 'pending_approval'

// If approved automatically:
// payment.status === 'completed'

Pricing model

Final pricing is provider and volume dependent. Sardis shows quotes before execution and applies platform spread only when policy allows it:

Production contracts expose provider pass-through fee + Sardis platform fee as separate line items.

Compliance Built In

All fiat operations integrate with our existing controls:

• Policy engine for limits and merchant/category controls
• Webhook replay protection for provider event ingestion
• Return-code controls (R01/R09 retry, R02/R03/R29 auto-pause)
• Append-only Ledger for audit trails

Withdrawals to new bank accounts trigger enhanced verification. Suspicious patterns are flagged before funds leave the system.

What's Next

Fiat Rails is available in sandbox and design-partner lanes. On the roadmap:

• International wires: SWIFT and SEPA support
• Multi-currency: EUR, GBP, and more stablecoins
• Recurring funding: Automated wallet top-ups
• Instant settlements: RTP for US payouts

Get Started

# TypeScript
npm install @sardis/sdk

# Python
pip install sardis-sdk

For enterprise pilots, reach out to efe@sardis.dev.

Fiat rails use regulated partner infrastructure. Sardis handles wallet management, policy enforcement, and compliance controls. Partners handle the actual fiat movement.