Ethereum block builder Eureka Labs has raised $6.7 million in a seed round as it looks to expand a new approach to block construction it calls "programmable blocks."

The round was co-led by Spark Capital and Collider Ventures and included participation from Varrock Ventures, Node Capital, Reverie, Very Early Ventures, Atka, Synergis, and Masterkey, alongside angel investors including CoinList president Scott Keto, Eureka Labs said Tuesday.

The round was completed in two tranches, with $4.7 million raised in April 2025 and an additional $2 million from Spark Capital in June 2025, Eureka Labs co-founder and CEO Nir Magenheim told The Block. The round was structured as a simple agreement for future equity (SAFE) with token warrants and is being disclosed now as Eureka Labs emerges from stealth, Magenheim said. He declined to disclose the startup's valuation.

Avishay Ovadia, founding partner at Collider Ventures, has joined Eureka's board as part of the funding round, Magenheim said.

Founded in December 2024, Eureka Labs has grown to become the fourth-largest Ethereum block builder by number of blocks built, according to Rated Network data. However, its market share is around 1.5%, as the three largest Ethereum block builders — Titan Builder, BuilderNet, and Quasar Builder — account for nearly 96% of the market, according to the data.

Programmable Ethereum blocks

Eureka Labs is introducing what it calls "programmable blocks," shifting blocks from passive containers of transactions into active execution environments.

Today, blocks package and order transactions primarily. Magenheim said Eureka's approach allows block builders to add logic during block construction, such as providing temporary credit or capital, running computations, or controlling how transactions execute together.

In practical terms, this enables new types of functionality at the block level, according to Magenheim.

One feature, "intra-block credit," allows users to access temporary loans within a single block without collateral, as long as the loan is repaid before the block is finalized. Another feature, "state-aware pre-computation," allows complex calculations to be run at block construction time using the exact state the block will have, reducing gas costs and improving reliability, Magenheim said.

The system also supports "execution-time external data access," allowing transactions to incorporate real-time off-chain data during block construction, and "deterministic transaction placement," which guarantees that certain transactions execute in a specific order within a block.

"This allows developers to rely on guarantees at the block level, not just inside smart contracts," Magenheim said. "For example, you can build applications that need large amounts of capital for a few seconds, depend on precise ordering, or require complex computation that wouldn’t normally fit onchain."

These features let developers rely on guarantees at the block level, not just within smart contracts, enabling more advanced trading strategies, more efficient DeFi, and new types of onchain applications, Magenheim said.

Eureka operates within Ethereum's Proposer-Builder Separation architecture, where block construction is handled by specialized builders rather than validators.

Magenheim said block builders could evolve into a new execution layer for Ethereum, similar to how smart contracts expanded the network's capabilities.

"We're only beginning to explore what becomes possible when blocks themselves become programmable," Magenheim said.

Eureka’s business model is based on collecting fees from transactions included in the blocks it builds. Based in Tel Aviv, Israel, Eureka Labs has a team of 12 people and recently opened an additional research and development site in Poland, Magenheim said, adding that the startup is hiring for technical roles across both locations.

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