Bitcoin’s security risk starts when one block gets far more fees than the next

Recent academic work highlights a previously under‑examined factor in Bitcoin’s security model: the size of fee differences between consecutive blocks. Using data from 2017‑2025, the study finds that larger fee gaps are associated with more competing blocks at the same height and a longer wait for the following block.

Fee gaps and mining incentives

Bitcoin miners receive a fixed block subsidy (currently 3.125 BTC) plus the transaction fees included in the block they mine. As the subsidy halves over time, fees become a larger component of miner revenue, though current measurements place fees at well under 1 % of total miner income.

Block‑level data show that fee rewards can vary dramatically from one block to the next. For example, an observed seven‑fold fee increase between two adjacent blocks illustrates how a prior block can become unusually valuable.

Block races and timing delays

The researchers define a “block race” as the presence of multiple blocks at the same height. Their analysis shows that larger adjacent‑block fee gaps correlate with a higher frequency of such races. Additionally, after a block with a high fee gap, the next block tends to appear later than in the first seconds, suggesting that miners may be contesting the previous height.

Mitigation through transaction lock‑fields

Bitcoin wallets can reduce the incentive for fee‑sniping by setting lock‑time or sequence fields that prevent a transaction from being included in a block earlier than intended. Wider adoption of these anti‑sniping measures would shrink the extra prize available to a miner attempting to rebuild a prior block.

Implementation is uneven: some Bitcoin Core RPC calls apply lock‑time by default, while others do not. The overall impact depends on how much transaction volume follows each code path.

Signals to monitor before the next subsidy cut

• Adjacent‑block fee gaps: Persistent or extreme gaps indicate periods when a prior block carries a larger extra reward.
• Competing‑block frequency: Changes in same‑height races reveal shifts in network behavior.
• Immediate next‑block timing: Delays in the first seconds after a high‑fee block align with the study’s findings.
• Lock‑field coverage: Greater use of anti‑sniping fields reduces the revenue available to a miner attempting a reorganization.

While transaction fees remain a small share of overall miner revenue, occasional outlier blocks can create short‑term incentives that affect network security. Monitoring the above signals offers a more nuanced view than aggregate fee statistics alone.