BIP 300 (Drivechains)

BIP-300 is the proposed Bitcoin consensus mechanism that would enable drivechains - sidechains where the peg between Bitcoin and the sidechain is enforced not by a federation, but by Bitcoin miners voting on withdrawal requests. Drivechains were proposed by Paul Sztorc in 2015 and remain one of the longest-running "should this activate?" debates in Bitcoin.

How drivechains would work, simplified:

1. A drivechain is launched with its own consensus rules. Users can peg-in BTC to it (locking the BTC on mainnet, receiving sidechain tokens).
2. Sidechain activity happens with whatever rules the sidechain implements (privacy, smart contracts, faster blocks, anything).
3. To peg-out, sidechain participants propose a withdrawal transaction to mainnet.
4. Miners vote on each withdrawal over a long period (~3 months). If enough miners support it, BTC is released back to mainnet. If not, it stays locked.

This is a two-way peg without a federated multisig. The trust assumption is: a majority of Bitcoin miners won't conspire to steal from drivechain peg-outs they don't approve, over months of voting.

The arguments for:

• Permissionless sidechain experimentation. Anyone could launch a drivechain with new features without needing Bitcoin protocol upgrades. Use cases: privacy chains (Confidential Transactions), high-throughput payment chains, alt-VM chains, etc.
• BTC remains the only token. No new altcoins; sidechain activity is denominated in pegged BTC.
• Bitcoin captures the fee economy of sidechains via merged mining (BIP-301).

The arguments against:

• Miner power expands. Drivechains formally give miners the authority to approve/deny peg-outs - a major shift from "miners just order transactions" to "miners hold custody."
• MEV pressure. Sidechains with rich economies could generate MEV that flows back to miners, potentially incentivizing concentration.
• Complexity. Drivechain support adds non-trivial validation logic to Bitcoin Core.
• Hype vs reality. Years of "drivechains will solve X" discourse without much built.

BIP-300 has not activated. Patches exist in some Bitcoin Core forks; the proposal cycles in and out of community discussion. As of 2026 it's not on a near-term roadmap, but the conversation hasn't died either. See BIP-301 for the companion merged-mining piece and Sidechain for the broader category.