Segregated Witness is officially locked in on the Bitcoin network after signaling threshold was reached during BIP 91 signaling period. The User Activated Soft Fork (UASF) movement, driven by node operators running the BIP 148 client, applied critical pressure on miners to signal support. After months of the blocksize war, SegWit lock-in at block 479,808 marked a decisive victory for Bitcoin's decentralized governance -- users, not miners or corporations, determined the protocol's direction. Activation would follow two weeks later on August 24.
Bitcoin Wiki: Segregated Witness