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After Activation identifies a split point, BIP110 and Standard miners may follow different views of validity. This page explains the simplified fork mechanics.
BIP110 and Standard miners share the same chain until a rule disagreement appears. Activation shows the two places that can happen: mandatory signaling, or later reduced-data rule enforcement.
Either a BIP110 miner or a Standard miner finds the first block after the split point. Suppose the first block is BIP110-compatible, so Standard nodes still accept it if otherwise valid.
Suppose the next block is mined by a Standard miner. It builds on top of the BIP110 block because that block is valid under its rules; Standard miners follow the valid chain with most accumulated work.
But this Standard block is rejected by BIP110 miners: it is not BIP110-compatible. So BIP110 miners keep working on the BIP110 tip, while Standard miners build on the Standard tip, leaving that branch a block ahead.
Let's say a BIP110 miner finds a compatible block on top of the shared split-point block. There are now two competing chains branching from the same point. This is a fork.
BIP110 miners only extend the BIP110-compatible chain; they reject blocks that violate the new rules. Standard miners extend whichever valid chain has the most accumulated work, or, in this simplified model, stay on their current tip when tied. Here another BIP110 block is mined first, so BIP110 takes the lead.
The BIP110 chain now has the most work, so Standard miners abandon their own Standard block (which is stale) and reorg onto the most work chain tip, which is the BIP110 chain.
Assume Standard miners find the next block, one that is not BIP110-compatible. BIP110 miners reject it, so they are behind again on their own fork.
Even if BIP110 now finds a compatible block, Standard miners do not switch in this model; they saw the other one first. So the two chains trade the lead, block by block. Whether BIP110 can pull and stay ahead depends mainly on how much hashrate is on the BIP110 side.
With a majority of hashrate, BIP110-compatible blocks are expected to accumulate work faster. Standard branches are repeatedly reorged, and BIP110 remains the chain with most modeled work while that majority holds.
If BIP110 has minority hashrate, Standard usually finds blocks faster. BIP110 may briefly catch up, but it keeps falling behind unless more hashrate enforces it.
The simulator lets you choose BIP110 hashrate and replay one reproducible fork sequence with the simplified model.
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