BIP 34 — Block v2, Height in Coinbase

BIP 34 (Block v2, Height in Coinbase) is a consensus soft fork requiring blocks to include their height in the coinbase transaction, deployed via a supermajority version rollout in the network's early soft-fork era (2012-2013). Making every coinbase unique addressed the duplicate-transaction-ID problem alongside BIP 30.

Debate relevance: Cited in soft-fork history timelines and in discussions of how early consensus changes were rolled out before version bits existed. Common misstatements: Attributing the duplicate-txid fix solely to BIP 34, or asserting exact activation dates from memory — the rollout used supermajority thresholds over time rather than a single flag day.