Ethereum activated Bellatrix, opening the final phase before the Merge

Ethereum activated the Bellatrix upgrade on its Beacon Chain at epoch 144896 at 11:34:47 UTC on September 6, 2022, beginning the final on-chain phase of the network’s planned transition from proof of work to proof of stake.

The activation was not the Merge itself. Bellatrix changed Ethereum’s consensus layer so Beacon Chain validators and their software could recognize and process the execution payloads required when the proof-of-work chain reached a separately defined difficulty threshold. Paris, the execution-layer stage, still had to occur before proof-of-work block production would end on the intended Ethereum network.

What Bellatrix changed

The Ethereum consensus specification in effect for the transition added an execution payload to the Beacon Chain’s block structure, along with rules for checking payload timestamps, parent hashes and validity through an execution engine. It also moved inactivity and slashing parameters to their planned maximum security values.

Those additions made the Beacon Chain “Merge aware.” Before Bellatrix, Ethereum’s proof-of-stake Beacon Chain operated in parallel with the execution layer that processed ordinary transactions. Bellatrix supplied the consensus-side machinery needed for validators eventually to assume responsibility for blocks containing Ethereum transactions.

The fork occurred at a predetermined epoch rather than at an estimated clock time. Ethereum’s Protocol Support Team had mapped epoch 144896 to 11:34:47 UTC on September 6. Contemporaneous reporting observed the upgrade activating at that epoch, while Ethereum’s official fork history subsequently recorded the same epoch, date and time.

One trigger remained

Bellatrix left Ethereum’s proof-of-work chain operating. The second trigger was a Terminal Total Difficulty, or TTD, of 58750000000000000000000. Once cumulative proof-of-work difficulty reached or exceeded that value, the Paris rules called for the next block to be produced under the Beacon Chain’s proof-of-stake consensus.

On September 6, the Ethereum Foundation’s published window for reaching TTD remained September 10 through September 20, 2022. The precise time was uncertain because it depended on proof-of-work hash rate. Bellatrix therefore established readiness for the transition; it did not prove that Paris would occur at any particular hour or that every operator had installed compatible software.

The distinction mattered operationally. Merge-ready nodes needed both an execution-layer client and a consensus-layer client, connected through the Engine API. The Foundation had warned that operators remaining on incompatible software after the applicable fork would follow old rules and would not participate in the intended upgraded network.

Why the activation mattered

For exchanges, custodians, staking providers and application infrastructure, Bellatrix converted the Merge from a published schedule into an active protocol state. That institutional significance is an interpretation of the technical event, not evidence that every service was prepared or that operational risk had disappeared.

For validators, the transition expanded responsibilities. After Paris, validators proposing blocks would need to verify execution-layer transactions and could receive transaction priority fees previously directed to miners. Beacon Chain withdrawals, however, were not enabled by Bellatrix or the Merge plan then in effect. Ether holders were not required by the protocol announcement to convert tokens or perform an account migration.

For miners, Bellatrix was the last consensus-layer step before the planned end of proof-of-work block production on Ethereum. Mining had not ended on September 6, because the execution chain had not yet crossed TTD.

No ether price or percentage move is attributed to Bellatrix in this reconstruction. Cryptoassets traded continuously across multiple venues, and the cited records do not provide a standardized ETH pair, exchange, UTC measurement window or methodology sufficient for a defensible event-day return or causal claim.

Later context

Ethereum’s official fork history records that the proof-of-work chain reached the specified TTD at block 15537393 on September 15, 2022, triggering Paris at the following block. That outcome confirms what followed Bellatrix but was not a completed event in the September 6 record.