**[Citrea Bitcoin ZK Rollup Mainnet Launches, Reigniting the Battle for Block Space]** BlockBeats reports that on January 29, the Bitcoin ZK-rollup project Citrea, backed by Founders Fund and Galaxy Ventures, officially launched its mainnet. The project introduces BTC-collateralized DeFi lending, structured products, and a native USD stablecoin, ctUSD, aiming to integrate "idle Bitcoin" into a comprehensive DeFi and payment ecosystem. Citrea stated that active DeFi liquidity during the initial phase of the mainnet launch is expected to reach $50 million. ctUSD is issued by MoonPay, pegged 1:1 to cash and short-term U.S. Treasury bonds. It is not a cross-chain asset but is natively issued on Citrea to reduce bridging risks and avoid liquidity fragmentation. The project has once again sparked controversy: as block subsidies decline, should non-payment use cases such as DeFi and stablecoins be leveraged to support Bitcoin miners' transaction fee revenue? Supporters argue this represents a sustainable source of demand, while opponents emphasize that Bitcoin block space should focus on simple, censorship-resistant payments. Notably, during Citrea's testnet phase, data availability usage accounted for nearly 10% of Bitcoin's monthly data bandwidth, indicating that Rollups could have a substantial impact on Bitcoin's block space.