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Circle sets the standard for security and institutional trust. When you handle real treasury yields, your infrastructure must match. That's why we integrated Modular Wallets.

We just completed the full integration of Circle Modular Wallets into Meridian Finance (themeridian.finance), our autonomous treasury yield infrastructure protocol on Arc Testnet.

Wanted to share the technical approach, what works, and one blocker we ran into.

We added passkey-based authentication (Face ID / Fingerprint / Windows Hello) as a second wallet option alongside the existing Reown/MetaMask/WalletConnect flow.

The goal: let users who don’t have a crypto wallet access DeFi treasury yields with just their biometrics. No seed phrase. No browser extension. No gas fees.

We built a unified wallet abstraction layer that routes contract interactions to the right execution path depending on the connected wallet type:

	1.	config/circle.ts - SDK configuration (Client Key, Client URL from Circle Console)

	2.	CircleWalletContext.tsx (~200 lines) Full passkey lifecycle:

	∙	toPasskeyTransport() for WebAuthn authentication

	∙	toWebAuthnCredential() with WebAuthnMode.Register (new users) and WebAuthnMode.Login (returning users)

	∙	Credential ID persisted in localStorage for seamless re-login

	∙	toCircleSmartAccount() for ERC-4337 smart contract account creation

	∙	createBundlerClient() with paymaster: true for gasless UserOperations

	∙	Full error handling (NotAllowedError, AbortError, cancelled prompts)

	3.	UnifiedWalletContext.tsx (~250 lines) - Unified abstraction:

	∙	executeContractWrite() routes to wagmi writeContractAsync (for MetaMask/Reown) OR encodeFunctionData + bundlerClient.sendUserOperation (for Circle)

	∙	waitForTransaction() uses the appropriate public client based on wallet type

	∙	Supports 3 wallet types: EVM (Reown), Circle (Passkey), Solana

	∙	Single hook (useUnifiedWallet) for the entire dashboard

	∙	“Connect Wallet” button (existing Reown modal)

	∙	“Passkey” button with Fingerprint icon (gold accent) - dropdown with Sign In (returning users) + Create Account (new users)

	∙	Smart Account indicator when connected via passkey

	5.	Dashboard page.tsx - Replaced 8 separate useWriteContract() hooks with a single executeContractWrite() from the unified context. Zero code duplication. All existing functionality (deposit, withdraw, claim yield, create/cancel streams) routes through the abstraction.

Client URL: https://modular-sdk.circle.com/v1/rpc/w3s/buidl

Passkey Domain: themeridian.finance (configured in Circle Console)

Client Keys: Separate keys for development (localhost) and production (themeridian.finance)

Transport: toPasskeyTransport for auth, toModularTransport for on-chain operations

	∙	Passkey registration via Face ID / Fingerprint - tested and confirmed on themeridian.finance (production)

	∙	WebAuthn credential creation and persistence across sessions

	∙	toPasskeyTransport + toWebAuthnCredential flow executes successfully

	∙	Biometric prompt appears correctly on mobile (iOS/Android) and desktop (Windows Hello)

	∙	Existing Reown/MetaMask wallet flow completely unaffected - zero breaking changes

	∙	The unified abstraction layer correctly routes based on wallet type

After successful passkey authentication, the flow fails at toCircleSmartAccount() with:

Error: The method “circle_getAddress” does not exist / is not available.

We investigated and found that toModularTransport() requires a chain-specific endpoint path. Looking at the Dynamic integration tutorial, the pattern is:

toModularTransport(${clientUrl}/polygonAmoy, clientKey)

Currently supported chains for Modular Wallets:

Arc Network is NOT in this list. The Circle RPC backend doesn’t have bundler/paymaster/smart account infrastructure deployed on Arc yet.

Since Meridian Finance is built entirely on Arc Testnet (our smart contracts YieldVaultV3.0.1, PaymentStreamV3.0.2, USYC integration - are all deployed on Arc), we cannot complete the Circle Modular Wallet flow until Arc is added to the supported chains.

The integration is architected so that when Arc support is added, we change ONE line:

import { polygonAmoy } from ‘viem/chains’

import { arcTestnet } from ‘../config/wagmi’

toModularTransport(${clientUrl}/arc, clientKey)

That’s it. Zero refactoring. The entire passkey -> smart account -> gasless transaction flow activates immediately.

📊 MERIDIAN FINANCE ON ARC - CURRENT STATS

	∙	YieldClaw autonomous agent running 24/7

Could the Circle team share any timeline or roadmap for Modular Wallets support on Arc Network?

Arc is Circle’s own L1, purpose-built for stablecoin finance. Modular Wallets on Arc would unlock passkey-based DeFi for the entire Arc ecosystem. We believe we’d be among the first protocols to activate it.

	∙	Transak on/off-ramp integration (Circle partner)

Happy to share more technical details, do a live demo, or provide feedback on the SDK. We’ve been building on Arc since testnet launch and are committed to the Circle ecosystem.

Circle Modular Wallets Integration on Meridian Finance - Technical Deep Dive & Arc Network Feature Request

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