Stacks
Stacks is a Bitcoin Layer 2 for smart contracts. Original 2017 ("Blockstack"), launched mainnet 2021. Major upgrade Nakamoto (2024) added near-instant finality and sBTC.
Architecture
- Separate chain: Stacks blocks reference Bitcoin blocks.
- Anchored: Stacks block hashes committed to Bitcoin via PoX.
- Smart contracts: written in Clarity (Stacks-specific lang).
- Native token: STX (used for fees, governance, staking).
- Native BTC peg: sBTC — 1:1 BTC-pegged asset on Stacks.
PoX (Proof of Transfer)
Consensus mechanism:
- Stacks miners burn STX (or send BTC, varies by epoch).
- Miners earn STX block rewards + tx fees.
- Stackers (STX holders who lock for ~2 weeks) earn BTC rewards from miner BTC contributions.
- Bitcoin's security secures Stacks via the BTC commitment.
Nakamoto upgrade
Activated in 2024. Major changes:
- Sub-second finality for Stacks-native transactions.
- sBTC activation: 1:1 BTC-pegged asset on Stacks via threshold signature signers.
- Bitcoin reorg robustness: Stacks chain remains stable through Bitcoin shallow reorgs.
Clarity language
Stacks's smart contract language:
- Decidable — can analyze contracts statically (no halting problem).
- No re-entrancy by design (contracts can't call themselves).
- LISP-like syntax.
- Source visible on-chain (no opaque bytecode).
(define-public (transfer (recipient principal) (amount uint))
(ft-transfer? token amount tx-sender recipient))
sBTC
- Bidirectional Bitcoin peg. Mainnet contracts deployed 13 December 2024; first completed deposit 14 December 2024; peg-outs live in practice 30 April 2025 (isolated first accepted withdrawal 25 March 2025).
- Signed by a permissioned institutional signer set — not the Stacking-elected Nakamoto block-signers; conflating the two is the usual source of confusion.
- Mainnet
sbtc-registryas of 15 September 2026: 11 signer keys,current-signature-threshold=u8(8-of-11); 14 keys /u10before the July 2026 rotation. - Key rotation is an access-controlled
rotate-keys-wrappercall only the current signer principal can make — seven rotations between December 2024 and August 2026, not tied to reward cycles. - Peg-in: send BTC to a P2TR output committing to the deposit script
- a reclaim leaf (sBTC 1.3.4, September 2026) → equivalent sBTC on Stacks.
- Peg-out: send sBTC + Stacks tx → BTC released after threshold approval.
Use cases
- DeFi on Bitcoin: lending, AMMs, derivatives using sBTC.
- Stable coins / RWA tokenization: programmable assets.
- DAO infrastructure: governance via Clarity contracts.
- Bitcoin-native NFTs: pre-Ordinals NFT scene.
Major projects
- ALEX — DEX/AMM on Stacks.
- Arkadiko — stablecoin protocol.
- STSWAP, Bitflow — DEX/AMM.
- CityCoins (historic, mostly inactive).
Comparison
| Aspect | Stacks | RSK | Liquid |
|---|---|---|---|
| Smart contracts | Clarity | EVM | Limited (Elements opcodes) |
| BTC peg | sBTC (threshold) | RBTC (federation + merge mining) | L-BTC (federation) |
| Consensus | PoX | Merge mining | Federation |
| Bitcoin security | Anchored | Inherited via merge mining | Federation only |
Implementations
- stacks-node (Rust) — full node.
- Stacks.js — JS / TS SDK for app dev.
- stacks-py — Python SDK.
- Hiro Wallet — primary wallet.
- Xverse Wallet — multi-chain Bitcoin wallet with Stacks support.
Limitations
- Threshold signer trust for sBTC peg-out — an 8-of-11 permissioned set as of September 2026; permissionless signer rotation is still outstanding.
- Smaller ecosystem vs Ethereum L2s.
- Clarity learning curve (vs Solidity ubiquity).