Fork Choice Rules

Function to choose between which proposed block becomes the head of chain.

Nakamoto Consensus

  • Choose highest total difficulty of blocks (which is not always equal to the length). Today used by Bitcoin, Ethereum (1), majority (if not all) PoW chains.
  • The chain is serial, each message (block) points to the next one.
  • Re-orgs are frequent (e.g. because two miners create blocks at the same time, and your miner didn’t see it)


  • Used by ethereum-2-pos. Names after LMD-GHOST1 + Casper.
  • Multiple messages can appear in parallel (in each slot).
  • Finality - once a block is finalized, it can not be reorged, except at a very high cost of slashing
  • Re-orgs are much more infrequent, for a block to be reorged it has to “defeat” all many thousand attesters (6000+)


  1. GHOST: Greediest Heaviest Observed Sub-Tree; choose chain that has most descendants 

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