Segwit activation

Segregated Witness (SegWit, BIP-141) activated on Bitcoin mainnet at block 481,824 on August 24, 2017 (01:57 UTC), after locking in on August 9, 2017 when a full signaling period reached the required miner threshold. SegWit was a soft fork that moved signature ("witness") data outside the transaction structure counted by legacy rules — fixing third-party transaction malleability (a prerequisite for safe Lightning channels) and replacing the 1 MB size limit with the 4M weight-unit system.

Nuance: Activation followed a contentious two-year period including UASF (BIP-148) pressure and the New York Agreement; the technical activation date is fact, but why miners finally signaled is still debated territory.

Common misstatements:

• "SegWit activated in 2016." — Proposed/released 2015–2016; activated August 24, 2017.
• "SegWit was a hard fork." — It was a backwards-compatible soft fork; legacy nodes continued validating the same chain.
• "SegWit removed signatures from blocks." — Witness data is fully inside blocks and committed to by them; it is restructured and discounted, not removed.