Introducing Citrea: Bitcoin's First ZK Rollup
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Introducing Citrea: Bitcoin's First ZK Rollup
Citrea's mission is to advance Bitcoin into its next phase, establishing it as the foundation of global financial infrastructure where developers can build anything on Bitcoin.
Navigating Web3 tides with focused insightsAuthor: Citrea Team
Translation: TechFlow
Today, we introduce Citrea—the first rollup to enhance Bitcoin's block space capacity through zero-knowledge technology.
Bitcoin scalability has long relied on solutions that move security and demand off-chain and beyond Bitcoin. Citrea aims to scale across the entire Bitcoin network using zero-knowledge proofs, ensuring on-chain verifiability and data availability within the Bitcoin network. This approach makes Citrea the first scaling solution capable of supporting more complex applications without compromising Bitcoin’s security or altering its consensus rules.
The Problem with Creating New Block Space
Bitcoin possesses the most secure, decentralized, and censorship-resistant block space. Scaling proposals that create new block space cannot inherit any of these attributes from Bitcoin. These proposals or implementations merely offer alternative block space; they do not extend the Bitcoin blockchain. Building sidechains with alternative block space competes with Bitcoin over the long term and exposes users’ funds to risks via insecure bridges and network constructs.
High Demand for Bitcoin Block Space
Due to its security, decentralization, and resistance to censorship, there is intense demand for all on-chain activities on Bitcoin. Over the past few months, we’ve observed exponential growth in interest for Bitcoin block space, reflected in rising fee rates. Whether for payments or inscription transactions, users want to get into blocks and are willing to pay for it. Ensuring sustainable participation in the Bitcoin network is critical for its long-term health and security budget—but there’s a trade-off: due to high fees and necessary block size limits, some transactions will inevitably be excluded. Crucially, Bitcoin must scale without changing its core principles to include more complex transactions.
This growing interest highlights a major flaw in existing scalability proposals: they fail to meet the increasing demand for inclusive Bitcoin block space.
Existing Scalability Proposals Do Not Scale Bitcoin
Bitcoin has long faced the challenge of processing more transactions and supporting broader applications without compromising its security or core principles. This multifaceted problem has proven difficult to solve comprehensively. Some projects have focused on scaling Bitcoin’s payment throughput—like the Lightning Network—while others aim to expand BTC asset functionality through sidechains. The former failed to bring programmability to Bitcoin, while the latter misses a key point: actively and effectively leveraging Bitcoin’s own blockchain.
In today’s landscape, intrinsic demand for the Bitcoin blockchain is redirected to separate consensus protocols and sidechains. This approach comes at a cost—sacrificing Bitcoin’s security and misaligning incentives—for lower fees and more BTC use cases. As a result, Bitcoin dominated by sidechains faces scalability solutions that fail to meaningfully serve its long-term health and incentive structure. While well-intentioned, these solutions don’t operate on the Bitcoin blockchain, contribute nothing to Bitcoin’s security, and ultimately cannot scale Bitcoin as needed.
Again, Bitcoin demand shifted to sidechains is no longer demand for Bitcoin.
Scaling Bitcoin Block Space
Truly scaling Bitcoin requires a symbiotic relationship between Bitcoin and the scaling solution. The scaling solution must actively and efficiently utilize Bitcoin’s block space to expand demand, increase expressiveness and throughput—all without changing the protocol. Scaling Bitcoin’s block space is the only way to transact with Bitcoin-level security. No other alternative can fully inherit Bitcoin’s security.
The safest and most incentive-aligned method to scale Bitcoin blocks is through on-chain verifiability and data sharding for execution. The only way to achieve easy verification on Bitcoin is by leveraging zero-knowledge or fraud proofs. Because fraud proofs require writing large amounts of data onto Bitcoin, ZK proofs are the most efficient way to verify execution validity within Bitcoin under block size constraints.
ZK Rollups create an execution shard, batch multiple transactions on that shard, and use succinct mathematical proofs along with minimal base data to verify them on-chain for state reconstruction. This enables ZK Rollups to utilize the underlying block space in the most verifiable and efficient manner, extending the L1 with full security.
Enter Citrea: Scaling with Bitcoin Security
Citrea is the first rollup on Bitcoin, enabling greater expressiveness and improved utility of Bitcoin block space without leaving Bitcoin. Citrea keeps Bitcoin demand within its own network and ensures the Bitcoin network serves as the data availability and settlement layer for Citrea transactions. Citrea requires no changes to Bitcoin consensus.
Citrea represents a major milestone for Bitcoin: it is the only Bitcoin-based execution layer on Bitcoin, the first with ZK proof verification, and the first general-purpose L2 validation inside Bitcoin. Citrea’s mission is to push Bitcoin into its next phase as the foundation of global financial infrastructure, where developers can build anything on Bitcoin.
Citrea batches thousands of transactions, processes them in a zkVM, and generates a succinct validity proof asserting the correctness of execution and output data. For the first time in Bitcoin history, Citrea’s validity proofs are inscribed and natively verified within the Bitcoin blockchain. Citrea builds a native ZK proof verifier smart contract on Bitcoin L1 using BitVM. Unlike monolithic sidechains, Citrea creates a modular world for Bitcoin through its execution sharding, keeping settlement and data availability on-chain—on Bitcoin.
Modular Bitcoin
Citrea creates stable fee revenue for miners through data availability, extends BTC beyond Bitcoin in a trust-minimized way via validity proofs, and allows developers to build anything on its EVM-equivalent execution shard.
Extending Bitcoin Security
Citrea is the only true execution layer on Bitcoin that settles on Bitcoin. Every transaction on Citrea is fully secured by zero-knowledge proofs and verified by Bitcoin. Citrea’s execution environment is trustless relative to Bitcoin and open to all participants in the Bitcoin network.
Thus, Citrea ensures it meets Bitcoin-equivalent guarantees for data availability, censorship resistance, and reorganization resistance.
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Bitcoin as the application foundation: Citrea’s mission is to build a programmable liquidity layer atop Bitcoin—the most secure and decentralized blockchain. We believe Bitcoin block space must be used efficiently to support various financial activities such as trustlessly buying, leveraging, or lending BTC. Most existing meta-protocols attempting to provide these functions are trusted and inefficient. Citrea is the most efficient and secure platform for building applications on Bitcoin.
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Bitcoin settlement and trust-minimized two-way peg: For the first time in Bitcoin history, a general-purpose L2 settles directly on Bitcoin, enabling the first-ever general-purpose trust-minimized two-way peg. Prior to Citrea, Layer 2 solutions relied on honest-majority assumptions via multisig, such as open or closed federations. With Citrea, as long as one network participant is honest, validity proofs can be verified on Bitcoin using the BitVM paradigm. BitVM is based on fraud proofs, meaning Citrea’s ZK proofs are optimistically verified on the Bitcoin network. In the future, a ZK proof verifier opcode will enable a fully trustless two-way peg mechanism.
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EVM equivalence: Building on Citrea with full EVM equivalence makes it easy for all EVM developers to build on Bitcoin. Citrea has released a fully EVM-equivalent Type 2 zkEVM built using RISC Zero. Citrea is not limited to a single VM by design and, thanks to its modular architecture, can adopt new VMs like WASM VM in the future.
What’s Next?
Internal Devnet Live
We are running the Citrea Devnet internally, using synthetic native BTC for critical infrastructure integration and testing. The trust-minimized two-way peg with BitVM is under active development.
Revealing the First Trust-Minimized Two-Way Peg
Stay tuned for details on Citrea’s trust-minimized peg design. We will announce our bridge design and open-source our codebase in the coming weeks!
Public Testnet
We’re moving fast. We’re actively building a robust testnet for the first rollup on Bitcoin. We look forward to sharing more information in the coming months. Follow our social media and blog.
Build on Citrea
Our developer contact form is open today. Citrea has been incubated by Chainway Labs for over a year and is well-funded. If you're interested in collaborating with us or deploying on Citrea, please reach out. Check our documentation to learn about Citrea’s technology.
Making Bitcoin the Foundation of Global Finance
Citrea’s vision is to build scalable infrastructure that pushes Bitcoin into its next stage as the foundation of global finance. To achieve this, we believe Bitcoin’s block space must be enhanced to include more transactions and offer greater expressiveness and functionality—without changing its consensus rules.
With its security, decentralization, and censorship resistance, Bitcoin is fully capable of becoming the foundation of global finance. Citrea builds on these strengths and enables Bitcoin to serve as the foundational layer for dynamic ecosystems like DeFi, gaming, NFTs, and more. As Citrea’s modular world grows larger and more advanced, it will only become stronger.
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