RPGF Nomination - ultra sound relay


My name is apriori. I nominate the ultra sound relay for Namada’s retroactive public goods funding program.


The ultra sound relay is a credibly-neutral and permissionless relay—a public good from the ultrasound.money team. The ultra sound relay emerged in 2023 to increase censorship resistance in Ethereum’s block production pipeline.

Motivation & Background

MEV creates an incentive for block producers to vertically integrate with trading firms to boost their returns. Unchecked, this is a centralizing force in Ethereum. One solution is a technique called (PBS) in which validators, proposers, can outsource block building to specialized parties called builders.

Today the Ethereum protocol runs an instance of Proposer Builder Separation (PBS) called mev-boost, an open source middleware run by validators to access a competitive block-building market.

With mev-boost, validators can access blocks from a marketplace of builders. Builders produce blocks containing transactions and a fee for the block proposer. Separating the role of proposers from block builders promotes greater competition, decentralization, and censorship-resistance for Ethereum. Today ~86% of Ethereum blocks (500 Epochs) were built with mev-boost.

The Relay

The role of the relay is critical in the supply chain as it coordinates the communication and commitments between builders and proposers. Relays aggregate blocks from multiple builders in order to select the block with the highest fees. The consensus layer client of a validator proposes the most profitable block received from mev-boost to the Ethereum network for attestation and block inclusion.

The relay is a contentious topic because of OFAC compliance. The most popular relay is the Flashbots relay. This relay filters transactions that involve addresses from the OFAC list. Since ~43% of the blocks are relayed by the Flashbots relay, roughly 59% of all blocks are OFAC compliant; previously ~ 69%.

This is a form of weak censorship. Weak censorship is mild transaction censorship which increases on-chain inclusion delay of censored transactions. For example, If 50% of the blocks are OFAC compliant, that means that only one in every 2 blocks will contain non-OFAC compliant transactions. Therefore, tthe average time of inclusion of these transactions will be 12 seconds/slot * (1/1-.5) = 24 seconds.


Today six of the eleven active relays do not censor OFAC transactions. The ultra sound relay is one of the non-censoring relays. As such, the ultrasound relay has made an immediate impact in a short time, relaying ~18.4% of remote built blocks over the prior 2 weeks.

(:heavy_check_mark: = non-censoring):

Relay Total Blocks % Total Blocks Chart
Flashbots 41,165 43.13% ██████████
BloXroute Max Profit :heavy_check_mark: 19,723 20.66% ██████
Ultra Sound :heavy_check_mark: 17,600 18.44% █████
Gnosis Agnostic :heavy_check_mark: 6,131 6.42% ██
Blocknative 5,643 5.91% ██
BloXroute Regulated 1,965 2.06%
BloXroute Ethical :heavy_check_mark: 1,371 1.44%
Eden 936 0.98%
Relayooor 409 0.43%
Aestus :heavy_check_mark: 336 0.35%
Manifold :heavy_check_mark: 168 0.18%

Open Source Contributions

The ultra sound relay is also contributing to the mev-boost stack by proposing a new innovation called the optimistic relay. The core idea is that you can improve the throughput and latency of block submissions by using asynchronous processing.

The reason to do this is because often winning bids come in near the end of a slot and the validation takes some amount of time because it is a call between the relay and the validation nodes. If we remove those extra milliseconds the winning bid can come in closer to the 12 second mark and thus contain more mev for both the builder and proposer. This directly improves the networks economic security; see Chitra & Kulkarni.

It is likely Optimistic relaying will become the standard for relays as those not runnin in optimsitic mode will not be able to compete. To read more about the motivations and design mechanism see this write-up.

Resource Constraints

Currently the ultrasound relay team is only two full time people. With the magnitude of impact the ultra sound relay is already having, RPGF could help them build out the team. The success of the ultra sound relay as well as that of the other non-censoring relays will allow Flashbots to deprecate their relay, which will have a significant impact in improving Ethereum’s censorship resistance until PBS is enshrined in protocol. At that time the relay will be superfluous.

Team Information

website: relay.ultrasound.money
contact: contact@ultrasound.money, Justin Drake