[Interview] Citrea: "We are Building the Bitcoin DeFi Infrastructure"

With trillions of dollars in Bitcoin sitting idle as a mere 'store of value,' the race is on to bring this massive dormant capital into the Decentralized Finance (DeFi) ecosystem. But can DeFi truly be built on top of Bitcoin? Citrea is the project born from this very question. Having recently launched its mainnet, Citrea is a step closer to becoming the 'Bitcoin DeFi infrastructure.' It is the first Layer 2 solution to combine a trust-minimized bridge with Zero-Knowledge (ZK) rollups. Today, Coinness met with Esad Yusuf Atik, co-founder of Citrea, to discuss the background, technical advantages, and future strategies of the project.

Q. Please briefly introduce yourself and the Citrea project. A: It’s a pleasure to meet the Coinness readers. My name is Esad Yusuf Atik, and I co-founded Citrea. I am also the co-founder and CTO of Chainway Labs, the developer of Citrea. We’ve been developing Citrea for the past two and a half years. Citrea is a Bitcoin Layer 2 solution—a rollup that uses Bitcoin as a Data Availability (DA) layer and for settlement. We successfully launched our mainnet about a month and a half ago.

Q. How would you define Citrea in one sentence? A: I would define it as the 'Bitcoin Application Layer' that supports access to Bitcoin capital markets for both institutions and individuals.

Q. What inspired you to start Citrea? A: In early 2024, our team was developing 'OrdinalSafe,' a wallet dedicated to Ordinals. Since we primarily worked with Ethereum and EVM-compatible chains, this was our first experience in the Bitcoin ecosystem, where we realized Bitcoin’s potential as a DA layer. However, the ecosystem lacked the DeFi infrastructure common on smart contract chains like Ethereum or Solana. Bitcoin script is extremely limited—it can do addition and subtraction but not multiplication. Moreover, it lacks the concept of 'state,' making it impossible to track token balances, which is essential for Automated Market Makers (AMM) like Uniswap. We wanted to find a way to use the trillions in 'dormant' Bitcoin for DeFi. While WBTC and other L2s existed, they relied on multisigs of a few entities. We believed true DeFi scaling couldn't happen through multisig. Thus, we began researching a bridge and rollup structure protected by the Bitcoin network itself.

Q. You advocate for a Bitcoin-based ZK-rollup Layer 2. What does this mean? A: For a network to function as a Layer 2 (L2) of a Layer 1 (L1), it must inherit the L1's properties, such as DA, reorg resistance, and verifiability. Citrea performs settlement on the Bitcoin network, inherits its reorg resistance, and uses it as a DA layer. ZK technology means all transactions are compressed into a succinct proof via ZK circuits. Citrea’s bridge, Clementine, uses this to verify the latest state on the Bitcoin network.

Q. Why does Bitcoin need ZK-rollup Layer 2? A: First, Bitcoin lacks native smart contracts. To use Bitcoin in DeFi, you must either bridge it to another L1 or build a dedicated Bitcoin L2 that inherits its security. The latter is superior as you don't have to trust a different chain. Second, we chose ZK because of Bitcoin’s low computational power. It’s easier to bundle all computations into a Groth16 proof to limit the steps needed for verification.

Q. Some argue that because L1 cannot verify ZK proofs, a Bitcoin native ZK-rollup isn't 'real.' How does Citrea overcome this? A: It's true Bitcoin cannot natively verify ZK proofs due to limited script functionality. However, the BitVM paper published in late 2023 solved this by introducing an 'optimistic game.' A Groth16 proof requires about 2GB of script, which exceeds a single block. BitVM V2 splits this into 4MB chunks. If a dispute arises, the system forces a re-execution of a specific 4MB segment to pinpoint data manipulation. Thus, Citrea is an 'optimistically verified ZK Rollup.'

Q. What is the architecture of Citrea? A: It consists of 'Citrea' (the EVM-compatible L2 rollup) and 'Clementine' (the Bitcoin bridge using BitVM V2 for dispute resolution). Clementine’s N-of-M multisig structure ensures the system stays safe as long as just one participant acts honestly.

Q. What does the recent mainnet launch signify? A: It’s the culmination of two years of hard work. It is the first actual realization of 'trust-minimized DeFi' on Bitcoin. Users can now bridge assets from Bitcoin or Ethereum, use LayerZero’s OFT bridge for USDC/USDT, and participate in the mainnet campaign to earn points through on-chain activities like trading and lending.

Q. You raised $16.7M from top VCs. Who are your key investors? A: Galaxy and Delphi Digital participated in the Seed round, while Peter Thiel’s Founders Fund led the Series A. Angel investors include Eric Voorhees, Balaji, and Jameson Lopp. Founders Fund is our most critical partner as they led the Series A.

Q. How is Citrea different from other Bitcoin L2s? A: The bridge. This is the first time a trust-minimized Bitcoin bridge has been implemented on a live network. Unlike others who rushed to launch using centralized multisigs, we participated in building BitVM to ensure maximum security. We didn't want users' Bitcoin sitting in a simple 3-out-of-5 multisig.

Q. Is there a Token Generation Event (TGE) planned? A: Specifics are TBD. However, we recently launched the Citrea Foundation to focus on decentralization and ecosystem expansion. The token will eventually serve to align the interests of all participants.

Q. Any final words for the Korean community? A: With the mainnet live, there are many opportunities for LPing and trading. We have a major announcement this month regarding how we will reward early users. We look forward to seeing you bridge your assets and join the campaign.