FAQ
General
Why is now a good time to build MPBC?
The transaction pipeline will undergo its most significant change in years through ePBS. ePBS improves the trusted hand-off of blocks to validators, while MPBC addresses other gaps in the pipeline. Shipping MPBC alongside this transition is an opportunity to replace relays operated as public goods with sustainably operated and competitive infrastructure in one step.
Is multi-party block construction compatible with trustless bids and P2P bids?
Absolutely. MPBC is fully compatible with ePBS and proposers are free to select whichever bid is most valuable, irrespective of the channel through which it arrived.
How does MPBC make blocks more valuable?
MPBC adds additional transactions to the most valuable block provided by any individual builder. Before delivering the block to the proposer, each MPBC layer operator double-checks that the multi-party block is more valuable than every alternative block it could provide.
How does MPBC benefit Ethereum's users?
MPBC reduces wait time and transaction costs, allowing users to transact more frequently. This is particularly valuable during high demand periods (for example, price volatility) when transactions cannot simply wait for the next slot.
What are your future plans for MPBC?
This is just the first step, and we will keep iterating with the community to improve the block construction pipeline. We expect a V2 that adds even more value late this year, and incremental upgrades along the way. While MPBC is currently limited to non-contentious transactions, the V2 aims to add more complex transaction types. A more detailed overview is provided in the Roadmap.
How can validators receive MPBC blocks?
MPBC upgrades the relay endpoints validators are already connected to. See Getting Started for details.
How will shared infrastructure providers like relays or operators work after ePBS?
Shared infrastructure providers like relays or operators will persist as these continue to provide services that increase block value, like MPBC or block propagation. In contrast to relays previously, MPBC layer operators are not mandatory escrow providers, but only used when their services yield the highest bid for validators.
Is being an operator permissionless?
The operator role and function are permissionless, as is the case for relays today. There is a public reference implementation that can be run by anybody, and builders and proposers can send and receive bids through any channel.
As in PBS today, builders must trust the MPBC operator or relay to send them flow. MPBC additionally also requires operators to trust each other as they share information. In the future, there can be economic and technological ways to reduce the need for trust and allow builders and operators to more easily interface with each other.
Who maintains the MPBC specs?
The MPBC specifications are developed and maintained by teams across the Blockspace Forum, a group coordinated to support open efforts to improve Ethereum's transaction pipeline.
How does MPBC improve censorship resistance?
Currently, a single builder holds full discretion over what goes into the block. With MPBC, filtered transactions can be added by other builders.
How does MPBC interact with FOCIL?
MPBC is fully compatible with and complements FOCIL. FOCIL guarantees inclusion for transactions the protocol is aware of. MPBC increases the probability of inclusion for transactions any builder is aware of through additional inclusion lanes (see Inclusion Lists and MPBC).
How do I keep up with the latest news and developments around block construction?
Learn more and follow our progress on our website and Twitter. We are building in the open and welcome feedback on our research and reference implementations.
Node operators
How do I start getting multi-party blocks?
You may already be receiving multi-party blocks if you are connected to relays today. Simply add the operator URLs to your sidecar's relay list documented in Endpoints.
Do I need new software?
No changes are required, your existing sidecar connects to operators like any relay. Optionally, Commit-Boost with the PBS module can take bids over a streamed connection for better performance.
How do MPBC operators handle OFAC compliance?
MPBC operators handle OFAC compliance like relays have in the past. Dedicated endpoints will continue to serve OFAC-compliant blocks.
I run DVT. Anything extra?
No. DVT validators carry no additional requirements and benefit from multi-party blocks immediately.
How does MPBC interact with validator timing games?
Validator timing games do not affect MPBC. Multi-party blocks are built continuously throughout the slot from the best single-party block available. The proposer always gets the most valuable block when it requests it, irrespective of the timing of the request. This can be a multi-party or a single-party block.
How does MPBC manage infrastructure outages?
Before you sign, your sidecar uses the best header from the operators that answered, the same as when any relay is unreachable today. After you sign, another operator can serve the payload, because operators share payloads with each other before the proposer signs.
Are multi-party blocks simulated before they reach me?
Yes, MPBC requires simulation. The operator must re-simulate the block because it has added new transactions to it.
How do MPBC operators handle invalid blocks?
The proposer is credited the value of the slot, the same way optimistic relaying compensates missed slots today. After ePBS an operator can also bid as a staked entity and pay unconditionally, see ePBS and MPBC.
Builders
What am I trusting the operator with?
Like relays, operators are trusted with the entire block. Operators may share payloads with each other to better propagate them to attesters. Multi-party blocks are always re-simulated as their state root changes due to the additional transactions they contain.
Who gets paid when multiple builders submit the same transaction?
The operator credits the builder that submitted a higher-value block containing the transaction. If bids are tied, the transaction is attributed to the builder that has submitted it earlier.
Does MPBC change how I price bids?
Builders continue to compete on the highest bid to increase their chance of winning the auction outright, having a block selected as the base block for MPBC, or landing transactions in a MPBC block.
Will my base blocks continue to compete in the auction?
Yes. If you make a block available for MPBC, the block will continue to compete in the auction. In addition, the multi-party block built on top of it will also compete in the auction.
How does MPBC benefit small builders?
Small builders can earn revenue without winning the slot outright by contributing transactions to MPBC blocks. They may also earn more for slots they win as flow gets appended to their blocks.
Can originators submit transactions directly to an operator?
No. Operators only accept blocks through the builder interface, therefore, an originator wishing to submit transactions directly would have to run a builder of its own. This is unlikely as such an ad hoc builder could only include transactions through MPBC, whereas existing builders can include transactions in base blocks and through MPBC.
How does MPBC interact with TEE builders?
Operators can be run inside TEEs to carry forward the trust guarantees issued by TEE builders and unify their flow with builders run on other hardware.
Do I need an API key to submit?
Standard block submission needs none. The dehydrated format, which omits transaction bodies the operator already holds, and the TCP stream typically require an API key. This policy is set by operators independently.
Does MPBC support blobs?
Yes, MPBC fully supports blobs.