Stacks

Stacks adds smart contracts to Bitcoin without changing Bitcoin. Its consensus mechanism, proof of transfer, has miners spend BTC to produce Stacks blocks, and that spent BTC is paid to STX holders who lock their tokens — creating Bitcoin-denominated yield from a separate chain.

Proof of transfer recycles Bitcoin rather than burning energy

Miners bid BTC for the right to produce a block. Instead of being destroyed, that BTC goes to STX holders who have locked their tokens. Security is anchored to Bitcoin's economics and the cost of mining becomes a transfer between participants rather than an expenditure on electricity.

Stacking pays in Bitcoin

Locking STX to support consensus earns BTC rather than more STX. Earning the base asset rather than an inflationary reward is unusual, and it means the yield is denominated in something with independent demand instead of in the token being issued to pay it.

Anchoring to Bitcoin's finality

Stacks blocks are settled onto Bitcoin, so reorganising Stacks history requires reorganising Bitcoin's. That inherits Bitcoin's settlement assurance for the anchoring, without requiring any change to Bitcoin itself — which is the entire point of the design.

Clarity is deliberately restricted

The contract language is not Turing-complete and is decidable, meaning a contract's behaviour can be determined before execution. That prevents entire classes of bugs at the cost of expressiveness, a trade that suits contracts securing Bitcoin-denominated value.

Why Bitcoin programmability is contested

Bitcoin's culture resists changes to the base protocol, so anything adding functionality must do so externally. Stacks is one approach; others take different routes. All of them trade some of Bitcoin's security properties for capability, and the honest question is how much.