Ethereum’s scaling challenges have led to a proliferation of Layer 2 (L2) rollups, which now process more transactions than the underlying Layer 1 blockchain. As these rollups mature, there is growing demand for atomic cross-rollup transactions that maintain consistency across separate L2 chains. Interlock is a cross-Layer 2 atomic transaction protocol enabled by a stateless Shared Sequencer. The Sequencer coordinates atomic transactions to reach consensus via messaging between rollups and the sequencer. Interlock ensures atomicity while allowing continuous optimistic processing of transactions that do not depend on the pending atomic cross-chain transaction state. This approach combines atomicity guarantees with optimistic execution, ensuring transaction validity across independent rollup chains.