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BIP-34 - Block Height in Coinbase

   
Year 2012
Type Soft fork (MASF)
BIP BIP-34
Status Active

What it does

Requires miners to include the block height as the first item in the coinbase transaction’s scriptSig. This ensures every coinbase transaction has a unique transaction ID.

Why it mattered

  • Prevented duplicate coinbase transaction IDs (which had occurred in blocks 91,842 and 91,880)
  • Made each block’s coinbase provably unique
  • Introduced the version-bits signaling mechanism later refined in BIP-9

How it activated

Miner-activated soft fork. Required 750 of the last 1000 blocks to signal support (75%). Activated on March 24, 2012.

Outcome

Smooth activation, no chain split. Became the model for subsequent miner-signaled soft forks.