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Bitcoin · First Principles

Part 8 · Modern Bitcoin

Bitcoin in 2026 is not Bitcoin in 2009. The base layer’s consensus rules have barely changed — that conservatism is the point — but a whole ecosystem of systems built on top of it has grown up: faster payment layers, parallel chains, new spending conditions, and unexpected uses of block space. This part is about those systems, and crucially about why each one exists.

The deep cryptographic and scripting mechanics live in Part 10 · Advanced — Taproot/Schnorr/MuSig2, timelocks and HTLCs, transaction malleability, and the soft-fork machinery. This part recaps those briefly and links to them, then goes where they don’t: the protocols and phenomena that those primitives make possible.

Roadmap

Section titled “Roadmap”
  1. SegWit & Taproot: the Soft-Fork Era — what the two landmark upgrades changed at a systems level (malleability fix, witness discount, Schnorr/Taproot privacy), and how each shipped without splitting the network.
  2. The Lightning Network — payment channels as off-chain 2-of-2 contracts, multi-hop routing via HTLCs, the penalty mechanism, and the tradeoffs of going off-chain.
  3. Sidechains, Statechains & Two-Way Pegs — moving coins to a separate system with different tradeoffs, and being honest about the trust assumptions involved.
  4. Covenants: Restricting How Coins Move — the proposed ability to constrain the next transaction’s shape, the use-cases (vaults, congestion control), and the recursion debate.
  5. Ordinals, Inscriptions & Data on Bitcoin — ordinal theory, inscriptions in the Taproot witness, BRC-20, and what the “spam” debate reveals about permissionless systems.

The recurring question, applied here

Section titled “The recurring question, applied here”

How do these systems preserve “untrusting strangers agree on one ledger” while adding scale and features? Some (soft forks) extend the base layer itself without ever weakening its rules. Others (Lightning, sidechains, statechains) move activity off the one ledger and lean back on it only to settle disputes — trading some of Bitcoin’s trustlessness for speed or flexibility. Keeping that tradeoff explicit is the throughline of this whole part.