Curve AMO
Both OTokens utilize Automated Market Operations (AMO). Origin uses the same battle-tested AMO design that was first pioneered by Frax. The AMO helps to maintain the peg, increases capital efficiency, and maximizes yields for OToken holders. The AMO is allowed to enact arbitrary monetary policy within a closed system so long as it does not negatively impact the peg. The protocol remains 100% collateralized at all times even as the money supply programmatically expands and contracts in response to market conditions.
The AMO helps to maintain the peg, increase capital efficiency, and maximize yields for OUSD and OETH holders.
Understanding Curve's MetaPool
MetaPools are Curve pools that allow for one token to trade with another underlying base pool. 3Pool is the most common base pool and it is the only one currently supported by our strategy codebase. For example, a TUSD MetaPool using 3Pool as its base pool enables users to seamlessly trade between TUSD and 3CRV (DAI/USDC/USDT).
Having 3Pool as a base pool is helpful in multiple ways:
Prevents diluting existing pools
Allows Curve to list less liquid assets
More volume and more trading fees for the DAO
MetaPool liquidity providers can then deposit the LP tokens to the Convex gauge to earn boosted CRV and CVX rewards.
OUSD uses a MetaPool to pair OUSD with 3CRV (USDT/DAI/USDC). OETH on the other hand uses a standard v2 pool to pair OETH with ETH.
How the AMO Works
AMM's count the number of coins on each side of the pool to determine the current price. In order to maintain the peg, both sides of a Curve pool must remain balanced. When the protocol deposits funds into a Curve pool, it deploys liquidity to both sides of the pool. For OUSD, it deploys OUSD on one side and 3CRV (USDT/DAI/USDC) on the other. For OETH, it deploys OETH on one side and ETH on the other. This ensures that after deploying liquidity, the balance of the pool doesn't change - since the protocol deploys equal amounts to both sides of the pool. When the pool contains more 3CRV than OUSD, the protocol deploys extra OUSD to bring the pool back into balance (but never more than a 1:2 ratio). Similarly, the protocol can deploy extra OETH if there is more ETH than OETH in the pool. This approach of providing (in most cases) double the liquidity to the Curve pools allows the protocol to earn up to twice as many rewards using the same amount of capital.
The AMO strategy collects and sells CRV and CVX tokens and the resulting collateral (stables for OUSD, LSTs for OETH) are added to the vault and show up in the form of extra units of OTokens in your wallet.
This feature can also also work in reverse, with the protocol removing extra OTokens from the pool when necessary to maintain the stability of the price. The AMO ensures the stability of the peg with far greater capital efficiency than previous models such as Maker's PSM which requires billions of dollars of USDC to be locked up as a stability mechanism for DAI.
Protocol Owned Liquidity
The OTokens deployed into the AMO are not minted by the Vault in a classic manner using backing collateral. Instead, the OTokens that are minted by the AMO is backed by itself. When the strategy removes liquidity from the AMO alongside 3Pool tokens, the OTokens are also removed and burned.
Remaining 100% collateralized is an important bedrock component of the protocol. The protocol owned OTokens held in the AMO is controlled by the protocol and it never enters circulation without being collateralized. When traders add or remove OTokens from the MetaPool, it has an effect similar to redeeming or minting since our strategy is capable of burning or creating new supply to maintain the pool's balance. Ultimately, OTokens can still be redeemed at any time for the underlying collateral on a 1:1 basis.
It may sound counterintuitive that the protocol can remain fully collateralized even while deploying unbacked collateral into the pool. Let's look at an example to understand how this is possible. Let's say 1,000 OETH/ETH has been deployed into the Curve pool by the AMO. This means the protocol owns 500 ETH and 500 unbacked OETH. A user comes along and swaps 100 ETH for 99.9 OETH. Notice that they receive slightly fewer units of OETH because of the trading fees and slippage. At the end of this transaction, the user is holding 99.9 OETH and the protocol is holding 600.1 ETH and 400 unbacked OETH. Since the user must transfer their ETH to the Curve pool in order to withdraw OETH, the previously unbacked OETH immediately becomes backed as part of the transaction. You can think of it as the vault pre-minting some OETH for Curve to sell on its behalf with those tokens become 100% backed the minute they enter circulation. The extra .1 ETH is owned by the liquidity provider (aka the protocol) and is distributed to holders as extra profit.
This model has been extensively tested and demonstrated to work safely at scale by the Frax team. In addition, the Origin team have also completed extensive testing in forked Mainnet node environment simulating how flash loans could mint large amounts, deploy liquidity and then redeem it, manipulating the AMO at various stages of that procedure. No vulnerabilities have been found. For safety, funds are never directly deployed or withdrawn from the AMO as a result of a mint or redeem. Like the rest of the code, the AMO has been thoroughly audited by OpenZeppelin and others.
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