Weβve seen time and again news headlines about how different cross-chain bridges have been compromised and hacked, so it is important for our community, users, and developers to have a clear understanding of the security models of the Celer Inter-chain Message Framework (Celer IM). Different from existing interoperability solutions, Celer has two different security models, an optimistic-rollup inspired model and a L1-PoS-blockchain security model. Each of these comes with different delay and security assumptions tradeoffs that developers and users can freely choose from or set. The security model is highly flexible and even for a single application, developers can choose to build a hybrid model based on the βvalueβ or βsignificanceβ of every cross-chain message.