The Bitcoin software contains the Bitcoin halving mechanism. Because the process is automatic, it is not dependent on any third party or central authority. When transactions occur on the Bitcoin network, they are stacked into groups known as blocks, and miners are rewarded for validating transactions within a block. When a total of 210,000 blocks are mined, the Bitcoin protocol automatically halves the reward miners receive.
So far, three Bitcoin halvings have occurred, the first of which occurred in 2012 after 210,000 blocks were mined, splitting block rewards from 50 BTC to 25 BTC. The second occurred in 2016 with the mining of the 420,000th block, which reduced the reward to 12.5 BTC. The most recent halving occurred in May 2020, further reducing mining rewards to 6.25 BTC. The final halving will occur in 2140, after which the reward system will be changed to only transaction fees.