The Bitcoin Cash (BCH) network underwent its first block reward halving on April 8 at 12:19 UTC. When block height 630,000 was reached, the mining reward was automatically reduced from 12.5 BCH to 6.25 BCH per block. This event had an immediate and dramatic impact on miner participation.
Miners operate under significant financial constraints. Managing thousands of mining machines requires substantial investment in hardware, time, and electricity. The 50% reduction in revenue made many mining operations unprofitable overnight. In response, miners quickly began shutting down their machines or reallocating their hash power to other networks, such as Bitcoin.
Data from cryptocurrency mining analytics site CoinWarz illustrates the severity of the decline. At the moment of the halving, both the network difficulty and the hash rate of Bitcoin Cash began to plummet.
The hash rate, which represents the total computational power dedicated to mining blocks, fell to 785 petahashes per second (PH/s). This represented an 80% decline from its peak of 4,001.5 PH/s recorded on April 8.
Network difficulty, a dynamic measure of how hard it is for miners to process a block, also saw a sharp drop. It fell to 269 billion, nearly 50% lower than the 528 billion recorded on April 8.
Security Implications of the Hash Rate Drop
This simultaneous collapse in both difficulty and hash rate raised serious concerns about the security of the Bitcoin Cash network, an eventuality foreshadowed by analysis from LongHash over a year prior.
According to data from Crypto51.app, a website that tracks the cost of launching a 51% attack to alter or erase blockchain transactions, attacking the Bitcoin Cash network for one hour would have cost approximately $9,121 at the time. This was equivalent to about 41.11 BCH. In stark contrast, launching a similar attack on the Bitcoin network was estimated to cost around $520,000—roughly 57 times more expensive. Even attacking the Ethereum network was costlier, at an estimated $85,377 per hour.
Crypto51 calculates these figures by estimating the cost of renting enough hash power from services like NiceHash to control 51% of a network's total computational power. It is important to note that NiceHash alone may not have sufficient hardware to overtake a major blockchain, but the metric remains a useful indicator for quantifying a network's security level.
A successful 51% attack would allow the attacker to take control of the blockchain, enabling them to reverse or erase transactions. This poses a significant risk to exchanges and other service providers, as an attacker could deposit coins, receive credit, then reverse the transaction to effectively double-spend their coins.
Bitcoin SV Follows Suit with Its Own Halving
Just over two days later, on April 10 at 20:48 UTC, Bitcoin SV (BSV) experienced its own first halving event. The block reward for miners was slashed from 12.5 BSV to 6.25 BSV, effectively cutting miner revenue on the chain by 50% as well.
Miners reacted swiftly. Mirroring the events on the Bitcoin Cash network, the hash rate and network difficulty on BSV began a steep decline.
Data from BlockChair showed that following the halving, the BSV hash rate dropped from 3.06 exahashes per second (EH/s) to approximately 1.83 EH/s—a decline of about 40%. Hash rate measures the total computational power miners contribute to securing the network.
This was directly reflected in the network difficulty. According to Satoshi.io, the network difficulty plummeted from 420 x 10⁹ down to 212 x 10⁹.
A tangible consequence of this miner exodus was a severe slowdown in block production. In the 15 hours immediately following the halving, only 35 BSV blocks were mined. This was 55 blocks fewer than what would be expected under normal conditions. Blockchains use network difficulty to regulate block times, aiming for a consistent average. The system is designed to adjust difficulty dynamically to ensure transactions are processed in a timely manner, but such a sudden drop in hash power overwhelms this mechanism.
The Root Cause: Miner Profitability
The fundamental reason for the synchronized decline in hash rate, difficulty, and block production time boils down to miner profitability.
A halving event instantly reduces the revenue for miners operating on that specific chain by 50%. This forces mining operators with thin profit margins to either power down their equipment or switch to mining a different, more profitable cryptocurrency. Fewer mining machines mean less computational power available to process blocks, which directly leads to slower transaction times and a less secure network.
While the price of BSV fell—at one point trading nearly $40 lower than BCH—the security of both networks did show signs of recovery from their lowest points following the initial crash.
Despite this partial rebound, the security of both the BCH and BSV blockchains remained significantly lower than it was just days before their respective halvings. Meanwhile, data from CoinWarz indicated that the hash rate of the Bitcoin network actually increased during this period, suggesting that the halving events on these fork chains pushed miners toward the more profitable and secure Bitcoin blockchain.
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Frequently Asked Questions
What is a block reward halving?
A halving is a scheduled event in certain cryptocurrency protocols where the reward for mining new blocks is cut in half. It is a deflationary mechanism designed to control the issuance of new coins.
Why does hash rate drop after a halving?
When the block reward is reduced, miner revenue decreases. If the value of the coin does not simultaneously increase enough to compensate, mining becomes less profitable. Miners then shut down their equipment or move to other networks, causing the total hash rate to fall.
What are the risks of a lower hash rate?
A lower hash rate makes a blockchain network more vulnerable to a 51% attack. With less computational power securing the network, it becomes cheaper for a malicious actor to rent enough power to potentially reverse transactions and double-spend coins.
Did Bitcoin experience a similar hash rate drop during its halvings?
Bitcoin has experienced short-term volatility around its halving events, but its significantly larger network effect, higher value, and immense security have historically prevented a catastrophic and sustained collapse in hash rate like that seen on BCH and BSV.
Can network difficulty adjustments fix the slow block times?
Yes, but gradually. Networks automatically adjust their difficulty downward after detecting slower block times. This process helps restore equilibrium, but it occurs over a period of blocks and cannot instantly resolve a very sudden loss of hash power.
Will the security of BCH and BSV recover?
Security can recover if the price of the native token increases sufficiently to make mining profitable again, attracting miners back to the network. The upcoming difficulty adjustments will also lower the barrier to entry for remaining miners.