Proposer-Builder Separation (PBS)

In early blockchain designs, the same node (the validator or miner) was responsible for both collecting transactions and ordering them into a block. However, as the ecosystem grew, "MEV" (Maximal Extractable Value) became a massive industry. Sophisticated actors realized they could make huge profits by reordering or "sandwiching" transactions. This created a problem: validators who were better at extracting MEV would earn more rewards, leading to centralization, as everyone would want to stake with the most "profitable" validator. Proposer-Builder Separation (PBS) was designed to solve this.

Under PBS, "builders" are specialized actors who compete to create the most profitable block possible. They use complex algorithms to pack transactions together, including MEV opportunities. They then "bid" for their block to be chosen. The "proposer" (the actual validator) doesn't see the contents of the block; they only see the bid amount. The proposer simply picks the highest bid, signs the block, and receives the payment. This ensures that even a simple, hobbyist validator at home can earn the same MEV rewards as a giant professional firm, because the "building" expertise is outsourced.

For investors, PBS is a critical part of the "MEV-Boost" ecosystem on Ethereum. It is what keeps the network decentralized by preventing "MEV centralization." However, it also creates a new centralized bottleneck: there are currently only a handful of major "builders" who construct almost all Ethereum blocks. This raises concerns about censorship, as builders could decide to exclude certain transactions. Future upgrades like "Enshrined PBS" aim to build this logic directly into the Ethereum protocol itself to make it more secure and resistant to builder-level censorship.