> For the complete documentation index, see [llms.txt](https://docs.zestprotocol.com/start/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zestprotocol.com/start/bitcoin-collateral-vaults/introducing-bitcoin-collateral-vaults.md). # Introducing Bitcoin Collateral Vaults ### The Problem we solve Bitcoin holders want to borrow against their BTC without surrendering custody. Today, this problem is solvable for institutional borrowers at scale. They deposit their BTC collateral in a segregated custody account in the qualified custodian (like Anchorage or Bitgo) and borrow against it. The lender has recourse through a tri-party agreement and the borrower retains title over their coins. However, this solution is not accessible at scale. Qualified custodians are expensive, require KYC/B onboarding, active loan management, only make sense for multimillion dollar loans, and even then the amount of loans is constrained by the workload that the people running the lending desk can handle. As a result, retail investors have to surrender custody over their BTC in order to borrow against it - be it to a bridge, wrapper or validator set - in exchange for synthetic BTC tokens that they can post as collateral in DeFi. Existing solutions require high trust requirements, making them unsuitable for the majority of Bitcoin holders. After all, Bitcoiners own a piece of the most decentralised computing network. They are right in not wanting to give that up. ### The Solution: Bitcoin Collateral Vaults Bitcoin Collateral Vaults allow users to post native Bitcoin as collateral and participate in DeFi without leaving the Bitcoin blockchain. The Bitcoin stays on L1 in a self-custodial vault. Smart contracts on DeFi chains like Ethereum manage the lending flow on the other side. Users keep custody over their Bitcoin while borrowing stablecoins from deep liquidity pools. The BTC never moves onto the DeFi destination chain, not even in a liquidation event. If a position is liquidated, the collateral is paid out natively on Bitcoin, and only as much of it as the debt actually requires: the remainder returns to the borrower's own vault, in BTC, automatically. Borrowers never hold a wrapped token, and never receive a synthetic IOU in place of their coins. Bitcoin Collateral Vaults isolate BTC collateral from DeFi tail risks like bridge failure, custodian failure, or failure of the destination chain. Even if the Ethereum blockchain goes down and never comes back online, the user gets their BTC back with nothing but their own key.
### How did Bitcoin Collateral Vaults become possible now? Recent advancements in BitVM have made it possible to build a future of self-custodial yet fully programmable BTC collateral. The Zest Protocol team has been building in the Bitcoin lending space since 2021. The team was amongst the first users of wBTC on Aave, but quickly realised that this approach wouldn't unlock the full potential of Bitcoin as the world's most pristine collateral asset. We joined Trust Machines in 2021 to work with Stacks Founder Muneeb Ali to build the world's first Bitcoin L2 with fully programmable smart contracts. We tinkered endlessly with Discreet Log Contracts (DLCs), FROST-enabled signer networks, and ended up spinning Zest Protocol out with the backing of Tim Draper and Yzi Labs to build the largest Bitcoin lending protocol on a Bitcoin layer. In early 2024, BitVM changed the landscape. For the first time, it became possible to verify arbitrary computations on Bitcoin without a consensus change. That meant zero-knowledge proofs could be checked on the Bitcoin base layer itself. A vault's spending conditions could be enforced by cryptographic proof of smart contract state on an external chain, not by a signer committee. The engineering has moved fast since then. On-chain challenge costs have dropped from over $14,000 with BitVM2 to sub-$100 with newer constructions. Today, production deployment has become realistic. Bitcoin Collateral Vaults hold BTC collateral in a UTXO on the Bitcoin base layer. BitVM verifies what happens on the DeFi chain and enforces the vault's spending conditions through cryptographic proofs. When a borrower repays or gets liquidated on Ethereum, a cryptographic proof of that event is submitted back to the Bitcoin vault. If the proof is valid, the BTC is released. If not, anyone can challenge it and block the withdrawal. This is the future of on-chain BTC backed lending. We understood the potential of Bitcoin Collateral Vaults in summer 2025 and have been building in stealth since. We now have a working mainnet prototype of Bitcoin Collateral Vaults and are accelerating towards Bitcoin mainnet deployment. ### Understanding Bitcoin Collateral Vaults Bitcoin Collateral Vaults reduce the trust model for Bitcoin-backed lending to its irreducible minimum: Bitcoin consensus and a single honest challenger. The mechanism is elegant. A user locks BTC into a Taproot UTXO on Bitcoin L1. The conditions under which that BTC can move are fixed at deposit and enforced by Bitcoin consensus itself — no party can add an outcome, alter an amount, or redirect a payout afterwards. Which outcome executes is determined by a zero-knowledge proof of the lending position's state on the destination chain, verified directly on Bitcoin via BitVM. {% hint style="info" %} Unlike designs where a Bitcoin vault can only ever be released in full, Zest Protocol's Bitcoin Collateral Vaults are **divisible**: the protocol settles at exact amounts against a single UTXO, on Bitcoin, in native BTC.\ \ The result is the best BTC-backed borrowing experience. Borrowers can top up Bitcoin Collateral Vaults at any time or withdraw excess collateral as Bitcoin appreciates. During liquidations only the collateral that the debt requires is taken. The remainder returns to the vault in native BTC. And perhaps most importantly, the borrower only needs their ordinary Bitcoin key to reclaim their BTC collateral - no recovery files or session artifacts. {% endhint %} Verification runs through an optimistic challenge protocol. To withdraw, a party posts a claim transaction on Bitcoin asserting that the relevant event has occurred (loan repayment for the borrower, liquidation breach for the liquidator). Any counterparty has a defined window to challenge. On the happy path, no challenge is raised and the withdrawal completes after the window for the cost of three Bitcoin transactions. If a claim is challenged, the claiming party must post a signed ZK proof of the asserted event. The challenge construction committed at vault creation makes invalid proofs self-incriminating: any signed-but-invalid proof leaks a cryptographic secret that the challenger posts on Bitcoin to block the withdrawal. Valid proofs pass; invalid proofs are caught with mathematical certainty. The implications are concrete. A Bitcoiner with 0.1 BTC can borrow stablecoins from the deepest pools in crypto without surrendering custody, without KYC, and without trusting any party other than Bitcoin and the destination chain. The product that today is gated behind tri-party agreements at qualified custodians, accessible only to multimillion-dollar borrowers, becomes available to every Bitcoin holder at any size secured by Bitcoin consensus itself. If the destination chain goes offline and never comes back, the BTC returns to the depositor with nothing but their own Bitcoin key. If every party other than the depositor and Bitcoin itself disappears, the BTC is still recoverable. This is what Bitcoin-collateralised lending is supposed to look like. BTC stays on Bitcoin, while stablecoins flow from where the liquidity already is. Verification happens on the chain that is most expensive to attack, and the trust assumptions reduce to the ones that secure Bitcoin itself. To dive deeper into the path to mainnet check out [How Zest Protocol brings Bitcoin Collateral Vaults to mainnet](/start/bitcoin-collateral-vaults/how-zest-protocol-brings-bitcoin-collateral-vaults-to-mainnet.md). For further technical details and integration opportunities with Bitcoin Collateral Vaults, contact the Zest Protocol team.