Rootstock (RSK) is the oldest attempt to give Bitcoin smart contracts — a live EVM sidechain since January 2018, secured by Bitcoin's own hashpower through merge-mining. For a developer it's the best of both worlds and a couple of sharp edges: your Ethereum tooling connects in one line because RSK runs the EVM, but two things behave differently enough to break naive code — gas is Bitcoin, and addresses use a different checksum. Get those two right and everything else is just Solidity. Here's the map for chain ID 30.
The essentials
Rootstock mainnet is chain ID 30, an EVM-compatible sidechain with:
RBTC as the gas token, pegged 1:1 to BTC via the PowPeg two-way peg. There's no separate inflationary token — you pay fees in Bitcoin, and RBTC shares Bitcoin's 21M cap. RBTC uses 18 decimals like ETH (so amounts are in wei-style units), but the value is BTC.
~30-second blocks — much slower than Ethereum's ~12s or an L2's ~2s. Fees are tiny, but your polling cadence and confirmation logic should assume half-minute blocks.
