SegWit (BIP141 family) Activated August 2017. Moved signatures and other auxiliary data into a new witness section that is not included in hashing. Goals achieved 1. Fixed transaction malleability for SegWit-only inputs. 2. Weight discount — witness bytes count 1 WU (vs 4 WU for base). Effective block size cap rose from 1 MB to 4 MWU. 3. Linear sighash (BIP143) — O(n) signing instead of O(n²) for multi-input txs. 4. Soft-fork upgrade path — version field on witness program enables future versions (1 = Taproot). Witness program structure for SegWit outputs: Version byte = (v0), (v1 = Taproot,…