BIP 49 — Derivation scheme for P2WPKH-nested-in-P2SH based accounts

BIP 49 (Derivation scheme for P2WPKH-nested-in-P2SH based accounts) standardizes derivation (purpose 49') for wrapped-SegWit accounts — SegWit outputs embedded in P2SH so older wallets could send to them during the transition. These produce addresses starting with 3. Repository status: Deployed.

Debate relevance: Mostly appears in recovery scenarios and in SegWit-transition history: why '3' addresses can be either multisig-era P2SH or wrapped SegWit. Common misstatements: Assuming every address starting with 3 is multisig, or that wrapped SegWit gets no witness discount — nested P2WPKH still benefits from SegWit's fee treatment, just less than native (BIP 84) outputs.