Beacon Layer also acts as an upgradeability layer for rollups attached to it via what we call Forkless Upgrades.
Forkless Upgrades allow a rollup to push a new runtime representing a change in the rollup’s state transition function, for example, introduction of a new opcode or changing the behaviour of a certain opcode in a backward-compatible manner.
Forkless upgrades leverage WASM. Rollup clients such as sequencers or other full-nodes do not have the rollup runtime hardcorded in the client. But instead, the nodes contain a WebAssembly execution host which is the environment in which the runtime executes. The host manages access or changes to the actual runtime. The upgrades to the rollup runtime are pushed in the form of on-chain WASM code, and the nodes then auto-sync with the new code at the specified blockheight via the host.