Stacks is a Bitcoin Layer‑2 secured by Proof‑of‑Transfer where miners commit BTC to mint STX and anchor blocks to Bitcoin every 10–15 minutes. Clarity smart contracts enable DeFi with Bitcoin finality, and the sBTC proposal aims to bring a two‑way peg for native BTC on chain. The Nakamoto upgrade scheduled for 2025 will reduce block times to five seconds and add probabilistic Bitcoin finality.