A new study finds that sharp differences in transaction fees between consecutive Bitcoin blocks can trigger more block races and alter miner incentives, raising fresh questions about the network's long-term security as subsidies decline
Bitcoin's security model is under renewed scrutiny as researchers highlight a risk that goes beyond the network's total fee revenue. According to a July 2026 working paper from the National Bureau of Economic Research, large differences in transaction fees between consecutive Bitcoin blocks are linked to an uptick in competing blocks at the same height-so-called block races-and longer waits for the next block. While the study's findings are observational and do not pinpoint individual miner intent, they suggest that the way fees are distributed from block to block can influence mining behavior and, by extension, network security.
Fee Gaps and Mining Incentives
Bitcoin miners currently earn a fixed block subsidy of 3.125 BTC plus transaction fees included in each block. As the block subsidy continues to halve roughly every four years, transaction fees are expected to play a larger role in sustaining miner revenue. Yet, recent data shows that fees remain a small fraction of total miner income-about 0.70% on August 26, according to Glassnode, and 0.67% for the week ending August 21, per BTC.network. Despite these low averages, block-level data reveals sharp swings: on August 26, Blockchain.com recorded 0.0077 BTC in fees for block 964,120 and 0.0536 BTC for block 964,121, a nearly sevenfold difference. Such volatility in block rewards can create incentives for miners to attempt to recreate a previous high-fee block rather than simply extending the latest chain tip.
Fee Sniping and Network Behavior
This incentive structure is described in Bitcoin Optech's "fee-sniping" scenario, where a miner may try to rebuild a prior block with unusually high fees, hoping to claim those rewards and then extend the chain from there. The economic appeal of this strategy increases when the fee gap between adjacent blocks is large and the expected reward for extending the tip is comparatively low. The NBER study found that larger fee gaps are associated with more frequent block races-instances where multiple blocks are mined at the same height-and a lower probability that the next block appears within seconds after a high-fee block. These patterns suggest that some miners may be diverting hash rate to contest previous blocks, though the study stops short of attributing specific motives to individual miners.
Wallet Protections and Implementation Gaps
Bitcoin wallets can reduce the incentive for fee sniping by using lock fields, which prevent certain transactions from being included in a block that replaces the current tip. However, the effectiveness of this protection depends on how consistently wallets and transaction-creation tools set these fields. For example, an open issue in Bitcoin Core from April 2026 notes that some transaction paths set nLockTime near the current block height, while others default to zero, resulting in uneven coverage. Broader adoption of lock fields could shrink the available reward for miners attempting to rebuild a previous block, but the real-world impact depends on how widely these features are implemented across the network.
Signals to Monitor Ahead of the Next Halving
With the next Bitcoin subsidy reduction on the horizon, several signals may offer a clearer view of network security risks than aggregate fee revenue alone. These include the size and persistence of adjacent-block fee gaps, the frequency of competing blocks at the same height, the timing of the next block after a high-fee block, and the consistency of lock-field usage across wallets. Each of these factors captures a different aspect of the incentive landscape for miners and may help users, developers, and researchers assess the evolving security budget as fee dynamics shift.
Recent market developments have also underscored the importance of monitoring network-level risks. As major exchanges wind down operations and institutional adoption of blockchain infrastructure accelerates, as covered in EgonCoin's analysis of crypto exchange shutdowns and institutional blockchain adoption, the resilience of core networks like Bitcoin remains a central concern for users and service providers alike.
According to data from Glassnode and BTC.network, transaction fees have consistently accounted for less than 1% of total Bitcoin miner revenue in recent months. On August 26, 2026, the fee reward for block 964,120 was 0.0077 BTC, while the following block, 964,121, saw a fee reward of 0.0536 BTC. These figures highlight the sharp variability in block-level rewards, even as aggregate fee income remains subdued.
Fee sniping illustrates how Bitcoin's security incentives can shift rapidly in response to short-lived fee spikes, even when overall fee revenue is low. The effectiveness of wallet-level protections, such as nLockTime and nSequence, depends on consistent implementation across transaction-creation tools and wallet software. As the block subsidy continues to decline, the network's ability to mitigate risks from fee-driven mining strategies will likely depend on both technical upgrades and user adoption of best practices.
