Citrea ZK-rollup launches, reignites Bitcoin block space debate
Citrea, a Bitcoin zero-knowledge rollup (ZK-rollup) backed by Founders Fund and Galaxy Ventures, launched its mainnet on Tuesday, introducing BTC-collateral lending, BTC-structured products, and a new U.S. dollar stablecoin, ctUSD.
The rollout is intended to channel what Citrea describes as “economically idle” Bitcoin (BTC) into collateral for decentralized finance (DeFi) and payment use cases while anchoring activity to Bitcoin’s base layer. The team projects active DeFi liquidity of $50 million within the first few weeks, with lending, structured products, and decentralized trading available at launch.
The debut has renewed a long-standing discussion over how Bitcoin’s scarce block space should be utilized. With block rewards declining over time, some developers argue that non‑payment applications are necessary to support miner fee revenue, while others maintain the network’s limited capacity should prioritize simple, censorship‑resistant payments over complex financial systems.
CtUSD targets Bitcoin stablecoin liquidity
CtUSD is issued by MoonPay, a regulated crypto payments and infrastructure company that provides fiat on- and off‑ramps for digital assets. The stablecoin is backed 1:1 by cash and short‑term U.S. Treasurys and is positioned as a compliance‑focused alternative to wrapped Tether (USDT) and wrapped USDC (USDC) circulating on Bitcoin‑adjacent networks.
Orkun Mahir Kılıç, co‑founder and CEO of Chainway Labs, the company behind Citrea, said ctUSD is “natively issued” on the rollup rather than bridged from another chain and is integrated with MoonPay’s Iron banking infrastructure. The setup includes banking‑grade rails such as virtual International Bank Account Numbers (vIBANs), enabling users to wire fiat that is automatically converted into ctUSD and settled onchain.
Why ctUSD’s ‘native’ structure is significant
Kılıç said that because Citrea is “the Bitcoin application layer anchored to Bitcoin’s security model,” ctUSD “inherits the security properties of the Citrea network itself.” He added that bridged assets “inherit the security risks of their weakest link,” whereas a natively issued stablecoin avoids external bridge exploits and is “not dependent on the solvency of a third‑party wrapping protocol.”
According to Kılıç, designating ctUSD as the single preferred stablecoin on Citrea aims to prevent liquidity from splitting across multiple wrapped versions of the same asset, reducing capital fragmentation and slippage for lenders and traders.
He said that combining a Bitcoin‑anchored rollup with a regulated stablecoin and banking integrations is intended to increase supply methodically and transition ctUSD “from a launch asset into the standard liquidity layer for the Bitcoin economy” over the next six to 12 months.
Citrea reported that during its testnet phase, its data availability usage alone accounted for nearly 10% of Bitcoin’s monthly data bandwidth at one point, indicating that pre‑launch rollup activity can consume a notable portion of block space.
Launch renews debate over Bitcoin block space
Bitcoin core developer and Casa chief security officer Jameson Lopp described the rollout as “the next grand experiment in generating sustainable demand for block space.”
However, one commenter argued that users are lending, trading, and settling on Citrea’s Ethereum Virtual Machine, with Bitcoin primarily storing proofs, effectively turning Bitcoin into a “filing cabinet” for rollup receipts. The commenter also cited Citrea’s single sequencer, an offchain treasury, and a “10‑party federation” as trust assumptions that shift, rather than eliminate, risk.
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