According to the "Fork choice rule" in Ethereum 2.0 (sharding), how to choose a branch in a fork? (A) or (B) ?

(A) branch, which has the most blocks in it. (similar to "longest chain" rule in PoW)

(B) branch with more attesters across all the blocks.

For example, assuming two following branches in a fork:

(1) branch one: including 10 blocks, signed by 8 unique attesters.

(2) branch two: including 8 blocks, signed by 10 unique attesters.

According to the "Fork choice rule" in Ethereum 2.0 (sharding), which above branch in this fork will be chosen? (1) or (2) ?

1 Answer 1


The fork choice rule in Ethereum 2.0 is called LMD GHOST.

The basic answer to the question is branch 2: the branch with the most attestations/votes.

There are many other details to the fork choice. For example, proposer boost, and votes are weighted by stake.





Visualising the 7-block reorg on the Ethereum beacon chain illustrates an unexpected outcome of the fork choice in action.

  • And what if all parameters (number of attestations/votes, the weight of votes according to their stake) are the same? In a such situation in PoW (where two branches have same difficulty) a set of miners work on branch (1) and others on branch (2). And what happens here?
    – Questioner
    Commented Mar 12, 2020 at 12:42
  • I think that uncle blocks aren't counted, see here github.com/ethereum/consensus-specs/blob/dev/specs/phase0/…
    – upavloff
    Commented Jun 8, 2022 at 19:04
  • @upavloff Thanks! Can't remember what made me think of uncles; fixed and updated the answer. The last link I added you'd likely be interested in case you haven't seen.
    – eth
    Commented Jun 9, 2022 at 10:17

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