Bitcoin Output Types and Address Formats: Evolution and Quantum Risk

This note traces how Bitcoin output types and address formats evolved between 2009 and 2026—P2PK (no standard address), P2PKH ("1…"), P2SH ("3…"), SegWit v0 ("bc1q…") and witness v1, mostly Taproot ("bc1p…")—and separates four layers that are often conflated: output type, locking condition, address encoding and wallet protocol. It then classifies the quantum exposure of the main output types by when a public key first appears on-chain: P2PK and P2TR reveal it at creation, whereas hash-based outputs reveal it when spent or through key reuse. Third-party estimates of exposed supply—about 6.26 million BTC as of January 2025, and over 34% of supply as of March 2026 according to BIP361—use different methods and cannot be summed. As of September 2026, quantum-resistance proposals remain drafts: BIP360 (P2MR) addresses only long-exposure attacks, and BIP361's sunset of legacy signatures depends on a post-quantum signature BIP that has not yet been numbered. The note is a systematic synthesis of the bitcoin/bips repository, Bitcoin Core source code and release notes, block data and published literature; it is not an independent on-chain measurement.