As the DAO discusses Timeboost, a new transaction ordering policy proposed for Arbitrum chains, there has been some confusion around what Timeboost actually does. As with anything new, we understand there are bound to be misunderstandings, so we wanted to clarify some of the most common misconceptions.
Misconception #1: Arbitrum uses the same model for transaction ordering and block building as Ethereum L1, so L1 MEV issues automatically apply to Arbitrum.
The reality: Arbitrum’s sequencing method is substantially different from Ethereum L1’s. Arbitrum uses a First-Come, First-Served (FCFS) model to determine transaction ordering, meaning that transactions are sequenced in the order in which they arrive. Arbitrum sequencing is also done continuously, rather than building each block all at once. This misunderstanding of Arbitrum transaction ordering leads to other misunderstandings of how Timeboost works.
Misconception #2: Timeboost Creates New Types of MEV Extraction.
The reality: Timeboost does not create new types of Maximum Extractable Value (MEV). Instead, it introduces slight adjustments to when and how existing forms of MEV operate. Timeboost is designed to strike a balance between capturing MEV value for the chain without introducing additional externalities.
For example, Timeboost does not enable transaction reordering in a way that facilitates sandwich attacks. The protocol does allow users to try to get their transactions processed earlier by gaining control of the express lane, but it doesn’t allow them to manipulate the order in which trades occur relative to others in the same block. This means the fast lane controller [at any given time] cannot be certain of how their transactions are ordered relative to others’ transactions.
Misconception #3: Timeboost gives the auction winner an unfair amount of power around transaction ordering.
The reality: Winning a Timeboost auction gives you a time advantage — specifically, a proposed 200ms “head start” — but it does not ensure your transaction will always be the first in every block. The perceived value of the express lane is pre-determined by its holder and how much they chose to bid to win control of it: it’s a use it or lose it privilege. Let’s be clear on what Timeboost does not do:
- It does not give anyone the right to reorder transactions. It does not let you see others’ transactions before they are sequenced (because the mempool will remain private).
- It does not ensure your transaction will always be the first in every block.
- It does not mean your tx will have absolutely zero total time delay. Winning the bid means you won’t experience the 200ms artificial delay others face, but natural delays — such as processing time or network distance — still apply.
Misconception #4: Timeboost will definitely be monopolized by powerful, centralized entities that ultimately harm the Arbitrum ecosystem.
The reality: Timeboost is designed as an auction-based system that encourages open competition. Although the idea of a monopoly can be scary, the auction process is still competitive. If one player dominates, they will be required to continuously outbid other users, which prevents complete static control. Additionally, the express lane only gives a 200ms time advantage. The system is designed to incentivize rational actors to participate when they believe there is an advantage to controlling the express lane and only bid up to the value they are willing to pay for that advantage (since it is a sealed-bid auction).
Finally, we want to stress that Timeboost is entirely optional, meaning that Arbitrum chains can still function normally without it. Should Timeboost need to be disabled, the network would smoothly revert to FCFS transaction ordering, maintaining its current security and efficiency. Every chain can make its own decision about whether to enable Timeboost–your chain, your rules.
Misconception #5: The goal of Timeboost is to capture all MEV value and completely eliminate spam.
The reality: As stated in the AIP, Timeboost’s goal is to provide a way for chain owners to capture a significant share of the MEV on their chain and reduce spam from FCFS arbitrage, all while preserving a best-in-class user experience with fast block times and protection against harmful MEV.
