This page answers common implementation questions about building with App Kit.

Arc builders now have a documented path to Pyth price feeds on Arc. With Arc testnet contract addresses published and a standard EVM integration flow documented, teams can start wiring real-time market data into smart contracts for collateral checks, quoting, liquidation logic, and price-aware settlement flows.

The first act of digital money brought dollars onchain and made them programmable, global, and widely accessible. But the next phase requires infrastructure built for businesses, institutions, and agents: stable USDC fees, sub-second final settlement, opt-in privacy, and payments that do not depend on human banking rails. Arc is built for that second act, where dollars do more than move. They work.

Arc is built for onchain finance, but serious finance apps need more than execution. They need market data, verified offchain inputs, and cross-chain interoperability. Chainlink gives Arc builders the infrastructure to start wiring those capabilities into products on Arc testnet.

Vyper's recent work on Arc Testnet brings three layers into one stack that rarely show up together: agent identity through ERC-8004, software-native settlement through x402 and Circle, and programmable financial controls like escrow, subscriptions, split payments, and spending limits.

CCTP is now supported on Stellar. In this Release Notes episode, @Hui Jing from Circle DevRel explains what changed, how Stellar fits into CCTP, and what developers should know when building USDC flows to or from Stellar. CCTP, or Cross-Chain Transfer Protocol, is Circle’s burn-and-mint protocol for moving USDC across supported blockchains. With Stellar support, builders can include Stellar in CCTP-powered USDC transfer flows. This episode covers: - Stellar’s CCTP domain ID: 27 - How CCTP message address handling differs on Stellar - When to use the CctpForwarder contract - Why user and muxed accounts need a USDC trustline - How Stellar’s seven-decimal USDC precision maps to CCTP’s six-decimal message amounts Resources: - Supported domains table: [https://developers.circle.com/cctp/concepts/supported-chains-and-domains] - Stellar contract addresses: [https://developers.circle.com/cctp/references/stellar-contracts] - Stellar technical overview: [ https://developers.circle.com/cctp/references/stellar ] - Quickstart: transfer USDC to and from Stellar: [https://developers.circle.com/cctp/quickstarts/transfer-usdc-stellar-arc ]

The final post in the Unified Balance Kit series covers the preflight checks and recovery paths apps need around spend(), especially when delegated flows or mint-side failures can affect execution.

Transaction memos on Arc give developers and businesses a way to attach structured context to onchain actions on Arc. That makes payments, payouts, deposits, withdrawals, and other financial workflows easier to reconcile, attribute, and connect to offchain systems.