The software that enables Ethereum nodes to read blocks from the blockchain and smart contracts is known as an Ethereum client. A "node" is a client program that is currently active. One must first download an Ethereum client program to operate a node. Various Ethereum client software with varying coding languages and code bases can run nodes.
By upgrading their consensus layer clients before epoch 144896 on the Beacon Chain, Ethereum node operators must abide by the Bellatrix update. This critical change, which integrates the PoS chain with the current execution layer, comes just before the Merge. In total, 73.5% of node operators were Merge ready before the Bellatrix upgrade, which meant that 26.5% of node operators had not yet updated their clients.
The Ethereum Foundation issued an alert that a client that remains non-updated will sync to the pre-fork blockchain.
Following the Bellatrix upgrade, there will be an official Merge named the "Paris Upgrade" between September 13 and 15. The Merge will occur when Terminal Total Difficulty (TTD) reaches 58750000000000000000000, at which point a Beacon Chain validator will create the following block, officially ushering in Ethereum's PoS era.
The second phase of Ethereum's three-phase transition process would complete with the eagerly anticipated changeover. Ethereum wants to become more accessible and energy efficient by switching to PoS.