August 24, 2017: the chain doesn’t change its face—it changes its spine. Segregated Witness, BIP141-143, goes live after a fiery summer of signaling, UASF, and debate. The idea is simple: move signatures outside the “stripped” part of the transaction, killing malleability and freeing space. The limit is no longer 1 MB but 4,000,000 weight units; in practice ~1 MB of base data + up to ~3 MB of discounted witness. vbytes are born, and blocks can finally breathe.

Fewer txid headaches, better batching, Lightning channels become practical. That day didn’t cause a pump; it caused order. A soft-fork activated via BIP9 after the August lock-in rewarded conservative engineering—no shortcuts, just better byte accounting.

Adoption climbed. Wallets migrated. Miners packed blocks by weight, not appearance. Fees turned more elastic: at the same congestion, more transactions fit. Spam incentives waned. Above all, building higher layers stopped being a promise and started being routine.

SegWit doesn’t “scale” everything by itself; it opens corridors. It’s the passage from a cramped hallway to an atrium with new doorways—where batching, Taproot, Lightning, and more now stand.

What’s the most underrated downstream effect of SegWit you’ve witnessed, and how did it change the way you use on-chain vs Lightning today?