A stable dollar, issued against a protocol-owned treasury of real assets.

What is Surplus

Two tokens and one treasury. Real assets set how many dollars can exist, and your PLUS sets how many you can borrow.

USDx is the dollar. It is built to trade at $1, and every USDx is minted against assets in the treasury.

PLUS is the governance token and the collateral. Lock it to borrow USDx, or use it to vote.

The treasury belongs to the protocol. It holds tokenized stocks and funds, cbBTC, WETH, and USDG. Its value sets how much USDx can be minted, and it keeps what it earns.

sUSDx is USDx staked in the stability vault. Stakers earn a share of borrower interest and absorb liquidations in exchange for discounted PLUS.

Coming from other DeFi protocols?

If you've used Liquity or Maker, borrowing will feel familiar: lock collateral, mint a dollar. Surplus adds a second limit. Total USDx supply also has to fit inside the treasury's assets.

Borrow USDx against PLUS

Lock PLUS and mint USDx to your wallet. You can borrow up to the smaller of two limits: your collateral limit and the shared headroom.

Max LTV adjusts to the market

On every borrow, the protocol compares the short-term and long-term PLUS prices. When they agree, you get the full max LTV. When they pull apart, max LTV shrinks toward a floor for new borrowing. As soon as prices settle, the full max LTV is back. Existing loans keep their own liquidation line, so a stress cut never liquidates anyone.

Loan details

• USDx is minted directly to your wallet.
• Add PLUS, withdraw extra PLUS, borrow more, or repay, all in one transaction.
• Anyone can repay a loan on your behalf.
• The smallest loan is 10 USDx. There are no monthly quotas or per-wallet caps.
• Locked PLUS votes again once you withdraw it.

Interest

Interest is charged on principal only, and it never compounds. The rate follows a kinked curve: low while total borrowing is light, rising quickly past the kink. Repaid principal is burned. Interest goes to sUSDx stakers and the fee split, which burns USDx and buys back PLUS.

Liquidations

When a loan passes its liquidation line, the stability vault absorbs it first. A public auction settles anything left, and the borrower gets back every PLUS that isn't needed.

For bidders

Auctions are open to any wallet, and bids can be any size. You get PLUS at the current auction price. Bids don't need a price feed, so auctions keep running even if an oracle is down. The maximum drop and window length are fixed when the contracts are deployed.

Auctions pause while the PLUS/USDx pool holds less USDx than half the remaining debt, so liquidations never dump PLUS into a thin market.

If an auction runs out of time

If the window ends with debt left, the account moves to recovery and its PLUS stays locked. Anyone can then repay the debt or start a salvage auction for the remaining PLUS. Debt only goes down when real USDx is paid.

The sUSDx stability vault

Stake USDx to earn a share of borrower interest and penalties, plus PLUS from the liquidations the vault absorbs at a discount.

How absorption works

When a loan passes its liquidation line, the vault burns its USDx against the debt and takes the loan's PLUS at the auction floor price, all in one transaction. The floor sits below the safe price, so the vault receives more PLUS than the USDx it burns would buy at the safe price. The PLUS is shared among stakers pro rata, and the vault never sells it.

The vault is sized to hold 5% to 10% of USDx supply. Borrowers keep their surplus collateral just as they do in an auction.

Bond assets into the treasury

Deposit an approved asset and choose your payout: USDx now, PLUS that vests over time, or a mix.

Every approved asset has a standing bond market. Governance approves the asset and sets its terms, and the market stays open with no vote needed for each purchase. On every bond, the contracts check the price, the custody, and how much of that asset the treasury already holds.

How the bond price moves

Every vPLUS grant adds to a shared pressure counter, which raises the PLUS price for the next bond. Pressure drains at a steady rate, so the price comes back down in quiet periods.

A discount can also apply, up to a maximum set by governance. Discounts switch on when PLUS trades above its treasury reference, and they grow:

• when the treasury holds less of your asset than its target, and
• when much of the USDx headroom is in use.

Burn USDx for PLUS

Burn USDx for vesting PLUS at the shared bond price. When USDx trades under $1, a peg discount applies and grows with the gap.

There is no fee to burn. Holders get a reason to take USDx out of circulation exactly when the peg needs support. Burns are capped each month, at 2% of supply in the research plan.

The treasury

A protocol-owned basket of tokenized stocks, crypto, and USDG. Its value sets how much USDx can exist.

All 12 launch assets are priced by Chainlink. Governance adds each asset by vote after checking its custody and pricing. In the research plan, USDG makes up about 40% of the treasury and doubles as its cash reserve, and USDx supply at launch starts at about half the treasury's value.

How much USDx can exist

Each asset gets a risk factor that reflects how easy it is to price, sell, and hold safely. The discounted values add up to the risk-adjusted treasury. Divide by the coverage ratio, which is at least 1, and you get the most USDx the treasury can support. What's left after current supply is the headroom.

Each asset has its own dollar cap. Assets are also grouped by issuer, by custodian, and by how closely their prices move together, and each group has a cap. The PLUS price never enters this calculation.

Run by rules any keeper can execute

Governance writes standing rules with set ranges and triggers. When a rule's conditions are met, any keeper can run it. Every action checks prices, slippage, cooldowns, and budgets before it settles.

A risk council posts the target share, and increases need governance approval. An incident report drops the target to zero. Required reserves always stay outside these positions.

A built-in recovery plan

If treasury assets fall far enough that USDx supply sits above capacity, a ladder of responses takes over:

Emergency sales are armed by governance in advance and run automatically. They only fire when a shortfall lasts three months after risk factors recover and USDx trades below $0.97, and they sell at most 5% of treasury value per month. Research settings.

Why USDx holds $1

Supply is capped by the treasury, demand comes from borrowers and the launchpad, and three stabilizers switch on below $1.

Prices you can trust

A custom Uniswap v4 hook reads the USDx/USDG and PLUS/USDx pools using short and long time-weighted averages. Chainlink prices the outside assets and USDG against the dollar. For lending and capacity the protocol uses the lower reading, and for spending it uses the higher one. Each reading needs a minimum of pool liquidity, and the treasury keeps a permanent PLUS/USDx position so that liquidity is always there.

Protocol fees buy back PLUS

Protocol fees are collected in USDx. By default, 25% is burned as USDx and 75% buys PLUS from the market and burns it.

Where the fees come from

• Borrowers. Interest and penalties, after the stability vault's share.
• The launchpad. 80% of the protocol's share of launchpad fees. The other 20% funds operations.
• Treasury liquidity. USDx fees earned by the treasury's pool positions.

How buybacks run

Anyone can trigger a buyback, at most once an hour. Each one buys from the main PLUS/USDx pool, the same one the price oracle reads, within tight price limits, and a failed buyback rolls back both the burn and the purchase. Fees are collected even when the pool or an oracle is down, and they wait until a buyback can run. Governance sets the split anywhere from 0% to 100% direct burn, and buybacks start paused until governance sets a budget that matches pool depth.

Launchpad

Launch a fixed-supply token priced in USDx. It graduates into a permanent Uniswap v4 pool where fees fall as market cap grows.

Trading tools

One order system covers market, limit, and TWAP orders on Surplus curves and pools, and on Pons markets too. Orders name the assets and your minimum price, not a venue, so they keep working after a token graduates.

Safety and governance

Core contracts are permanent. PLUS holders tune settings through a timelock, inside hard limits written into the code.

Ten rules the contracts enforce

Each rule is covered by the Solidity test suites, including invariant tests that run long random sequences of actions.

Who controls what

Every governance change passes through a timelock, so everyone can see it before it takes effect. A risk council can pause new borrowing or treasury markets right away, and only governance can lift a pause. Repaying and bidding keep working during a pause.

Details for the curious

Launch parameters

Things to know before you use Surplus

• A falling PLUS price can push your loan past its liquidation line. Keep an eye on your LTV.
• USDx trades on open markets, and its price can move away from $1.
• Tokenized stocks and wrapped crypto depend on their issuers and custodians.
• Smart contracts can contain bugs. Independent audits are part of the launch plan.
• sUSDx stakers take on liquidated PLUS. If PLUS falls below the price the vault paid, stakers lose value.
• Limit and TWAP orders fill only when a keeper executes them, so a brief price touch may not fill.
• Launchpad tokens can be very volatile.