Orphan Block

An orphan block (also called a stale block) is a valid block that was successfully mined but not included in the main blockchain. This happens when two miners find a valid block at approximately the same time — the network accepts one and discards the other.

How orphan blocks occur

1. Two miners (or pools) solve a block simultaneously
2. Both broadcast their block to the network
3. Different nodes receive different blocks first and temporarily have conflicting chain tips
4. The network converges on the longer chain — the block in the shorter branch becomes orphaned
5. The miner of the orphaned block receives no reward — the block reward and fees are lost

Impact on miners

• Lost revenue — orphaned blocks mean wasted work and no reward
• Higher orphan rate at large pools — large pools with high hashrate find blocks more frequently, but high latency between pool members increases orphan risk
• Orphan rate — the percentage of orphaned blocks is a key pool efficiency metric

Orphan blocks in DAG chains

In DAG-based blockchains like Kaspa, blocks that would be orphaned in a traditional chain are instead included in the DAG structure and can still earn rewards — reducing wasted work.

See also

• Orphan rate
• Block
• Latency
• DAG