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SegWit Activation

#481824 · 2017/08/24 · Technical

Segregated Witness (SegWit) was activated, fixing transaction malleability and increasing block capacity. It also enabled second-layer solutions like the Lightning Network.

This event is part of Bitcoin history — See the full Bitcoin timeline

A Major Protocol Upgrade

On August 24, 2017, Segregated Witness (SegWit) was activated on the Bitcoin network at block #481824. SegWit was a soft fork that fixed transaction malleability — a long-standing bug that prevented complex smart contracts and second-layer solutions from working securely on Bitcoin.

SegWit works by separating (segregating) the witness data (signatures) from the transaction data. This allowed more transactions to fit in each block (effectively increasing block capacity to ~4 MB) and fixed the transaction malleability issue that had plagued Bitcoin since its early days.

Impact and Legacy

Upgrade Type

Soft Fork

Block Capacity Before

1 MB

Block Capacity After

~4 MB (weight units)

Key Fix

Transaction malleability

Enables

Lightning Network

SegWit's activation paved the way for the Lightning Network, a second-layer scaling solution that enables instant, low-cost Bitcoin payments. Today, the majority of Bitcoin transactions use SegWit addresses, and the Lightning Network has grown to support thousands of nodes and millions of dollars in payment capacity.