Block Design

The goal of Radius is to optimize the use of blockspace in a way that protects users and maximizes rollup profits to ensure the sustainability of the rollup ecosystem.
When rollups use a first-come-first-serve (FCFS) ordering mechanism, they can prevent MEV but must sacrifice potential profits from blockspace auctions. On the other hand, if rollups prioritize profit generation through blockspace auctions, it allows for MEV extraction.
Dividing the Block
To address this rollup dilemma, we propose dividing the block into two sections: the top blockspace and bottom blockspace. The top blockspace is dedicated to user transactions, where users send encrypted transactions to the sequencer. This effectively protects users against harmful MEV and censorship by preventing manipulation of transaction ordering.
In the bottom blockspace, we introduce an auction-based open marketplace for traders. Traders can create bundles of cross-rollup benign MEV transactions such as arbitrage, liquidations, and backruns. Traders then submit the bundled transactions along with their bids to the sequencer, who selects the bundle with the highest bid to include in a block. This approach maximizes rollup profits from cross-rollup transactions while fostering an efficient market for rollups.
For details on our proposed optimized blockspace design, see Ethereum Research.