"The most profound economic changes come not from replacing existing players, but from transforming their roles and incentives within the ecosystem." — Vitalik Buterin

## One-Block Delay and Referencing Order-Invariant Actions in Based Rollups:

Based rollups can reference current Ethereum state, but they still face a simulation challenge regarding the next block's state. A based rollup builder constructing rollup block alongside Ethereum block does not know the exact state of Ethereum that will exist after Ethereum block is finalized.

This leads to a general one-block delay in referencing the host state because the rollup cannot reference the current, still-determining Ethereum state. However, a zero-block time lag on communication between Ethereum and a based rollup is possible in a specific scenario: if the rollup block references only the outcomes of order invariant actions on the host chain.

When a based rollup block is submitted atomically with such order invariant actions on Ethereum, the rollup's state transition function can confidently read the outcomes of those specific actions in the same block, maintaining simulatability. This mechanism allows for faster host-to-rollup communication by focusing on the subset of host chain outcomes that are predictable and non-contentious.

Gloated Rollups are a special case for zero-block communication L2' when referencing predictable, order-invariant actions included atomically on the host chain.

## Builders as a Service

In XGA, Builders, who previously controlled entire blocks, now face a market where:

* They may lose exclusive access to the most profitable positions (Top of Block) through increased competition.

* They must adapt their strategies to include on Rest of Block (RoB) construction.

* They face potential margin compression as value flows directly from searchers to validators, bypassing them completely.

Builders can create more value as specialized service providers than as general gatekeepers. This points towards a future where block construction becomes a sophisticated, multi-layered market of specialized services rather than the current simple auction for priority (i.e. Flashbots).

This transformation doesn't eliminate builders' importance—it enhances it by expanding their role from simple block constructors to essential service providers that optimize the entire transaction lifecycle, from submission to inclusion to execution.

Builders can create significantly more value for the entire ecosystem—users, protocols, and validators—by offering specialized services rather than merely acting as toll collectors. This shift unlocks new economic opportunities and fosters a more efficient market, especially in a Rollup centric roadmap for Ethereum.