While smart contract systems of today have the capability to be deployed with permissions, upgradeable proxies, and ways to add extra logic to them, the unique selling point of this technology has always been its ability to remain immutable and predictable after the initial deployment. Systems with these properties can be used reliably by integrators with strong expectations that they will continue working as expected. From a smart contract security perspective, this allows users and builders to rest easy knowing that the code they are transacting with now will not change and surprise them.