The Bellatrix Upgrade for the Ethereum Beacon Chain [PoS chain] was completed successfully at 11:34 AM UTC on the 6th of September, 2022.
The upgrade was scheduled to happen at Epoch 144896 of the Beacon Chain. Note that in the Beacon chain epochs signify predictable time periods that are further sub-divided into slots.
Contrast this with the PoW chain where the latest block height would signify a reasonably predictable time period. Before this upgrade, node operators are expected to update their clients to the latest version to be able to participate in the ecosystem during and after the Merge. Vitalik and other Ethereum leaders took to Twitter earlier to remind folks to upgrade their clients. Vitalik also re-confirmed the September 13-15 timeline for the Merge.

The Bellatrix Upgrade makes the Beacon Chain (or the PoS consensus chain) prepared in a steady state for the eventual merge. The next and final step in the Merge process would be the Paris Upgrade where the switch will happen to the PoS chain for consensus. This is scheduled to happen at a Terminal Total Difficulty [TTD] of 58,750,000,000,000,000,000,000. This would coincide with a real-world date of around September 14/15th.