Roberto Bayardo May 1, 2023 Background EIP-4844 introduces a new blob transaction type for which SSZ encoding was chosen for its network & block representations in place of RLP. The choice of SSZ kicks off a longstanding desire to migrate the Ethereum execution layer (EL) to this more modern and featureful encoding format, which is expected to yield multiple benefits over time. In the short term, once there are enough SSZ transaction types to cover all transaction use cases, new L2s/zk-EVMs can avoid implementing the legacy RLP transaction support entirely, eliminating significant technical debt. Transactions in the execution layer have two perpetual identifiers: sig_hash, a hash of the unsigned transaction data which the signature is based on, and tx_hash, the signed transaction's hash, used as a unique identifier to refer to the transaction.