SegWit activates

Segregated Witness (SegWit), specified in BIP 141, activated at block 481,824 on August 24, 2017. It moved signature data into a separate part of the transaction. That fixed transaction malleability and let blocks hold more transactions without raising the old 1 MB base size limit.

Because older nodes still saw SegWit blocks as valid, it was a soft fork, not a hard fork. It also paved the way for the Lightning Network and, later, the Taproot upgrade in 2021. See our full SegWit explainer.