The Bitcoin network is expected to see its largest ever negative difficulty adjustment today of over 27%, retargeting from 19.9T to ~14.4T. The retargeting is expected to occur later today (50 blocks from the time of writing).
“Difficulty” is the metric used to describe how hard it is to mine a new block. The higher the network’s difficulty, the more compute power is needed on average by miners to find the next block hash. As Bitcoin’s price and difficulty fluctuate, miners become more or less profitable and turn on or shut off hardware accordingly creating a sort of homeostasis.
Bitcoin’s difficulty adjusts every 2016 blocks based on the time taken to mine the previous set of 2016 blocks. By targeting a block mining time of 10 minutes, the 2016 blocks should take 2 weeks to mine; as hash power is added or subtracted from the network within this period, however, block mining times can become temporarily shorter or longer respectively.
Block mining times have steadily increased over the current difficulty period, indicating the large difficulty adjustment to come:
With the recent exodus of Chinese miners following government crackdown on the industry, miners are shutting off hardware and moving operations elsewhere. Kazakhstan, Miami, Texas, El Salvador, and other more miner friendly locations around the globe are rapidly gearing up for the influx of new machines.
While there is a near term down spike in hashrate for the Bitcoin network, the large scale migration and dispersion of mining equipment adds further decentralization and security in the long term, as others have pointed out.
Besides the long term implications on mining decentralization: the difficulty readjustment should merely reduce block times making transactions confirm noticeably faster, and will increase the profitability for miners which will put even more pressure on those leaving China to deploy their hardware.