First 100 Post-halving Bitcoin Blocks: Miners Readjusting, 51% Attack Gets Cheaper

As the Bitcoin (BTC) network is adjusting after its third mining reward halving, first signs of the falling hashrate are starting to appear, while block time, which should, in theory, be around 10 minutes, dropped to 1 minute on multiple occasions as first 100 post-halving blocks are being mined.

While there is no specific data point on how much hashrate has dropped just yet, Johnson Xu, the Chief Analyst at token data and rating agency TokenInsight, estimates it’s around 15%. now shows that hashrate dropped by 3% in the past 24 hours (10:33 UTC) and this number keeps growing, as just a few hours ago it still showed an increase.

At the same time,, a website that tracks costs of a 51% attack on a cryptoasset network, shows that such an attack on Bitcoin is now more than 50% cheaper than it was yesterday – one hour attack would cost around USD 375,000, or the same as in April 2019. To compare, it still costs four times more than the same attack on the Ethereum (ETH) network.

"The network participants need to take a bit more time to readjust their positions, thus we expect, in the coming days, there should be some volatility in the hashrate itself and especially going into the next difficulty adjustment," Johnson said. Major Bitcoin mining pool now estimates that mining difficulty, a measure showing how hard it is to compete for mining rewards, should increase by 4.7% to 16.82 T, or above its March all-time high, in 6 days.

Because miners were hastening the block time pre-halving, in terms of the current BTC difficulty epoch, it’s roughly 53 blocks ahead of the network schedule, said Xu.

In the 24-hour period leading to the Bitcoin halving block, the network was producing on average 1 block per roughly 8 minutes, as miners were pushing the block to be faster. However, according to Xu, immediately after the halving, miners were mining slower than before halving, at c. 12 minutes per block, while the rate increased later. Some blocks are still being found in a few minutes and less. However, "12 hours into the 6.25 bitcoin subsidy era, the average block time has returned to nearly 10 minutes per block," Xu said, noting that "the block production time could shift significantly within 6 days as miners are trying to get their head around on what’s next for them."

Meanwhile, the share of miner revenue from fees jumped immediately after the halving, but the total sum of collected fees dropped, Xu added.

(This article will be updated when more data about the status of the network becomes available today).


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