Miners are hurting Bitcoin, says developer. Why?
Antoine Poinsot, developer and collaborator of Bitcoin Core, posted on August 5 on X a criticism of a growing trend among Bitcoin miners: Congratulations Summer-1sat/vb, you managed to ruin compact blocks.
His comment points to a recent change in the behavior of the miners, who in recent weeks have included transactions with rates below 1 satoshi per virtual byte (sat/vB), a unit that measures the cost that users pay for processing their transactions on the Bitcoin network.
This phenomenon, known on social networks as the Summer sub-1sat/vB, has challenged the policies of relay (retransmission of the nodes and, according to Poinsot, exposes vulnerabilities in the compact block protocol, an optimization introduced in 2016 through the proposal to improve Bitcoin 152 (BIP-152).
What are the compact blocks of Bitcoin, and how would they be damaged?
Compact blocks are a mechanism designed to accelerate the spread of new blocks in Bitcoin.
Before BIP-152, the nodes transmitted complete blocks, which consumed bandwidth and time.
Compact blocks solve this by sending a summary of transaction hashes, assuming that the nodes already have many of them in their mempool (space where outstanding transactions are stored). If data is missing, the nodes request the necessary data, thus reducing network traffic.
However, this system depends on the mempools of the nodes being similar. The current conduct of the miners, which includes sub-1 sat/vB transactions, breaks this premise.
Miners traditionally prioritize transactions with high rates for profitability. Now, faced with high demand for space, some miners fill blocks with cheap transactions, possibly through external economic agreements or maximization strategies.
Since many nodes reject these transactions for relay policies (such as a minimum of 1 sat/vB), they do not have them in their mempool, forcing additional requests and affecting the efficiency of the system.
The injury noted by Poinsot
Poinsot warns that this Summer sub-1sat/vB. Hass “ruined” the compact blocks. The damage lies in an increase in latency and the use of resources. Normally, a compact block requires less than 0.2 MB of additional data for reconstruction.
Currently, as stated by the bitcoiner collaborator, the nodes must discharge up to 0.8 MB per block, eliminating the advantage of reducing propagation time. This adds rounds of communication between nodes, countering BIP-152’s purpose of minimizing delays.
The following chart, provided by Antoine Poinsot, shows the average size of transactions that Bitcoin nodes must request daily to rebuild compact blocks, measured in kilobytes (kB).
The above image data covers from 1 May to 6 August 2025, with each cell representing one day and each row a specific node on the network. The color scale ranges from green (low values, ideals) to red (high, problematic values), indicating that a smaller size is preferable for efficiency.
In May and June, most cells are green, with average sizes below 100 kB, reflecting efficient operation of compact blocks.
Starting in July, especially in recent weeks, yellow and red tones predominate, with peaks reaching about 800 kB (0.8 MB) per day. This coincides with the Summer sub-1sat/vB, where miners have included transactions with rates below 1 sat/vB.
This situation nullifies the expected efficiency, where compact blocks reduced traffic to fractions of a megabyte, and now equals or exceeds the traditional complete shipping method. In other words, the network is working harder than necessary, as if it had to ask for full instructions instead of a summary.
Network impact and possible solutions
The problem mainly affects miners and node operators. The former see their blocks spreading more slowly, reducing competitiveness, while the latter face higher bandwidth consumption.
For ordinary users, who send transactions with standard rates, the direct impact is limited, but in the long term, it could generate congestion and increases in rates.
Poinsot suggests adjusting the relay policy, as proposed by Bitcoin Core’s PR, which lowers the minimum to 0.1 sat/vB, aligning nodes with mining reality. However, this measure requires consensus, and the Summer sub-1sat/vB could reflect experiments or pressures for structural changes.
The situation underlines the need to adapt the protocol to emerging economic dynamics, a continuing challenge for Bitcoin.
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