Citrea is the world's first ZK Rollup built on Bitcoin, developed by Chainway Labs. Using BitVM technology, it brings full EVM-compatible smart contract capability to Bitcoin without changing a single line of the Bitcoin protocol. This means every DeFi protocol, DEX, lending platform, and NFT marketplace that runs on Ethereum can now work on Citrea — secured by Bitcoin, the most battle-tested blockchain in the world. This article explains how Citrea works, why BitVM is a breakthrough, and what opportunities Bitcoin L2 opens for users and developers in 2026.
- What is Citrea? Background & Origin
- What is BitVM? The Foundation of Citrea
- How Does a ZK Rollup on Bitcoin Work?
- cBTC: Bitcoin Ready for DeFi
- Citrea vs Ethereum L2: Similarities and Differences
- Bitcoin DeFi on Citrea: What Can You Do?
- Citrea vs Competitors: Stacks, Lightning, Merlin
- Risks and Considerations
- FAQ
What is Citrea? Background & Origin
Citrea was developed by Chainway Labs, a Turkish company founded in 2022 by Orkun Mahir Kul and a team of cryptography and ZK systems engineers. Their core mission: make Bitcoin the world's most secure settlement layer for programmable finance.
Before Citrea, developers who wanted to build smart contracts on Bitcoin had two poor options: (1) use a Bitcoin sidechain like Liquid or RSK with security trade-offs, or (2) abandon Bitcoin entirely for Ethereum and its L2 ecosystem. Citrea changed this equation by building a ZK Rollup that settles directly on Bitcoin mainnet.
In 2025, Citrea launched its testnet attracting developers worldwide, before launching its mainnet — a historic milestone: the first time EVM programs ran under real Bitcoin security.
What is BitVM? The Foundation of Citrea
To understand Citrea you need to understand BitVM first. BitVM is a framework proposed by Robin Linus in late 2023 to solve the problem that Bitcoin Script has limited capabilities — it doesn't support Turing-complete computation like Ethereum does.
BitVM works using optimistic verification on Bitcoin Script: normally, off-chain computation is accepted without proof, but if someone finds fraud, they can open a "fraud proof challenge" on Bitcoin. Bitcoin Script can then verify who actually cheated.
Citrea extends BitVM by using ZK proofs instead of optimistic challenges. Rather than waiting 7 days for a challenge period like Optimistic Rollups, every batch of Citrea transactions comes with a ZK proof. This proof mathematically proves all transactions in the batch are correct. Bitcoin script verifies the proof via the BitVM Verifier, enabling immediate finality with stronger security guarantees.
How Does a ZK Rollup on Bitcoin Work?
Citrea's process works in five key steps:
1. User submits a transaction on Citrea: Users interact with DApps on Citrea exactly like using an Ethereum L2. MetaMask, Hardhat, and Foundry all work natively.
2. Sequencer batches transactions: The sequencer receives user transactions, orders them, and bundles thousands together into a batch.
3. ZK Prover generates a proof: Citrea's ZK Prover computes a Zero-Knowledge proof that all state transitions in the batch are valid — without revealing individual transaction details.
4. Proof posted to Bitcoin: The ZK proof and state root are sent to Bitcoin mainnet via a special transaction using the BitVM Verifier script. Bitcoin script verifies the proof, and if valid, confirms the batch.
5. Immediate finality: Once Bitcoin confirms the transaction, Citrea's state is final — backed by the full weight of Bitcoin's security.
This entire process lets users enjoy fast, cheap DeFi on Citrea while the BTC used as collateral remains safely on Bitcoin mainnet.
cBTC: Bitcoin Ready for DeFi
cBTC (Citrea Bitcoin) is the native token used on the Citrea network — a 1:1 representation of Bitcoin on-chain.
How to get cBTC: Users send BTC to a bridge contract on Bitcoin mainnet secured by multisig and ZK verification. The bridge mints cBTC on Citrea at a 1:1 rate. To withdraw, burn cBTC on Citrea, and the bridge releases the real BTC on mainnet.
What can you do with cBTC?
• Trade on DEXes on Citrea, similar to ETH on Uniswap
• Use as collateral to borrow stablecoins on lending protocols
• Provide liquidity and earn yield
• Buy NFTs and in-game items
• Pay gas fees for smart contract execution
Citrea vs Ethereum L2: Similarities and Differences
Those familiar with Ethereum L2s like Arbitrum, Optimism, or Base will find Citrea very familiar — but there are key differences.
Similarities: Both use EVM and Solidity developer experience, can easily port DApps from Ethereum, offer much lower fees than mainnet, and have higher throughput.
Key differences: Ethereum L2s settle on Ethereum L1, deriving security from Ethereum consensus. Citrea settles on Bitcoin L1, deriving security from Bitcoin — the chain with the highest hash rate in the world and 17 years of battle-testing.
Additionally, Ethereum L2s use ETH as their native asset and gas, while Citrea uses cBTC (1:1 with real Bitcoin). This lets BTC holders participate in DeFi while staying entirely within the Bitcoin ecosystem.
Bitcoin DeFi on Citrea: What Can You Do?
Since Citrea's testnet launched, its ecosystem has grown rapidly:
Decentralized Exchanges (DEX): Trading pairs between cBTC and various tokens using familiar AMM models.
Lending & Borrowing: Use cBTC as collateral to borrow stablecoins or other tokens — letting BTC holders access liquidity without selling their Bitcoin.
Yield Farming: Provide liquidity to pools and earn fees and rewards.
Bitcoin-backed Stablecoins: Overcollateralized stablecoins backed by cBTC — similar to DAI on Ethereum but secured by Bitcoin.
NFTs: Mint and trade NFTs using cBTC, with Bitcoin-level security for proof of ownership.
Bridges to Ethereum: Cross-chain bridges enabling asset movement between Citrea and Ethereum ecosystem chains.
Citrea vs Competitors: Stacks, Lightning, Merlin
Citrea vs Lightning Network: Lightning is a payment channel network for fast micropayments between two parties — it doesn't support smart contracts. Citrea supports full EVM DeFi. They're complementary, not direct competitors.
Citrea vs Stacks: Stacks uses its own Proof of Transfer (PoX) consensus with Clarity language. While it anchors to Bitcoin, it's not a true ZK Rollup — finality isn't cryptographically guaranteed by Bitcoin in the same way. Citrea has a stronger security model mathematically, but Stacks has a larger existing ecosystem.
Citrea vs Merlin Chain: Merlin is also a Bitcoin L2 using ZK Rollup technology, but uses Ethereum as its DA layer in part — making the security chain longer. Citrea settles directly on Bitcoin, which is architecturally cleaner.
Citrea vs BOB (Build on Bitcoin): BOB is an Ethereum L2 with a Bitcoin bridge — it's an Ethereum L2 with Bitcoin assets. Citrea is a Bitcoin L2 with EVM — fundamentally different security assumptions.
Risks and Considerations
Despite being an exciting innovation, users and investors should be aware of the following risks:
1. Bridge Risk: Locking BTC in a bridge contract to receive cBTC carries smart contract risk. Even with ZK verification, bridge contracts can have bugs.
2. Sequencer Centralization: In early phases, the sequencer is centralized — it could theoretically censor transactions or front-run, though it cannot steal funds due to ZK proofs.
3. ZK Proof Technology is Young: ZK systems are highly complex and have a history of bugs on other platforms. Code needs thorough auditing.
4. Bitcoin Block Space Costs: Every batch must post a proof on Bitcoin, subject to Bitcoin's fee market. During high congestion, Citrea's operating costs increase.
5. Small Ecosystem: Bitcoin DeFi's TVL is still a fraction of Ethereum's. Users must accept lower liquidity during the early phase.
Frequently Asked Questions
Conclusion
Citrea marks a historic moment for Bitcoin — opening the door for Ethereum-grade DeFi to run under Bitcoin security through ZK proofs and BitVM. For EVM developers, porting projects to Citrea requires almost no code changes. For BTC holders, cBTC unlocks Bitcoin as a productive asset through lending, yield farming, and DeFi — all without leaving the Bitcoin ecosystem. That said, Bitcoin DeFi is still in its early stages: bridge risks remain, sequencer centralization needs addressing, and the ecosystem TVL is small compared to Ethereum. Those interested should research thoroughly and start with amounts they can afford to risk.
This article is for educational purposes only and does not constitute financial advice.
