The Vibe: The 2017 Bitcoin upgrade that fixed transaction malleability and increased effective block size — making BTC faster, cheaper, and ready for Lightning Network.
The Details: SegWit (Segregated Witness) was a soft fork activated in August 2017. It separated (“segregated”) signature data (witness) from the main transaction data, solving:
- Transaction malleability (which could let signatures be tweaked, breaking things like Lightning channels).
- Block size limit — by moving signatures outside the traditional 1 MB block limit, more transactions fit per block (effective capacity ~1.7–2 MB or more with high SegWit usage).
Compatibility note: SegWit is fully backwards compatible with legacy addresses (starting with “1”). You can safely send BTC from a legacy address to a SegWit address (starting with “3” for nested/P2SH-SegWit or “bc1” for native/Bech32), and vice versa — transactions always succeed, with no risk of lost funds. This seamless interoperability was a deliberate design choice via the soft fork.
SegWit addresses (especially native “bc1” Bech32 format) offer cheaper fees, better error detection, and stronger security. They unlocked second-layer solutions like the Lightning Network for instant, near-zero-cost payments. In 2026, most wallets/exchanges use SegWit (or even newer Taproot) by default; legacy addresses (starting with “1”) are outdated and more expensive.
Pro Tip: Always use SegWit (native Bech32) addresses for lower fees and compatibility with Lightning. Check your wallet settings — switching to SegWit can save money on transfers. SegWit is why Bitcoin scaled without hard forks.