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Yearn <> CoW Swap

Yearn partners with CoW Swap

tl;dr; After months of working on a yearn cowswap solver, we reached production ready code. Starting from today you will be able to do complex swaps in CoW Swap like, 3CRV <-> yvSNX.
Yearn is committed to settle all strategies trades through CoW Swap and trying to get as much cows as possible to increase users revenue.


Typical Yearn strategies deposit capital into a protocol for yield and sometimes the strategy claims additional tokens which are converted to the user’s wanted token.

An example: There is a yvDAI strategy that is depositing DAI in curve’s 3POOL. The liquidity pool token is staked to earn CRV. After some time, the CRV is converted to DAI.

If you verify strategies’ code, you will see that often there is a hardcoded path on where to do rewards -> want trades. A typical approach is using a uni-v2 compatible smart-contract. While this approach is working fine, there are pitfalls:

  • Transaction fees
  • Optimal path is not static
  • MEV protected harvests are complicated
  • Can’t settle trades against other strategies and/or internal liquidity

We found out that working with CoW Swap would allow us to tackle our concerns and leap into the future.


At Yearn we want to continue evolving our code to be as decentralized as possible. It would have been easy to set a path for a trade from an off-chain service, but we want to make sure we are not the only ones offering a solution. While we will participate in the orders bidding inside CoW Swap, the field is open for someone else to find a better solution and we encourage you to do it. The more competition in the CoW Swap ecosystem, the better settlements Yearn’s users will get.


To improve our settlement prices we decided to invest in Weiroll. Weiroll brings the possibility of having a small virtual machine inside a smart contract. The big benefit for a solver is the possibility of chaining interactions without leaving dust behind.

Let’s use an example to explain its power. Let’s say we want to do the following trade:


If we use the CoW Swap settlement contract, a solver would be sending a list of interactions which does the following:

  1. Approve WETH on 1 inch
  2. Swap WETH for SNX in 1inch
  3. Approve SNX in yvSNX
  4. Deposit SNX in yvSNX

There are two issues here.
First, is it ok for CoW Swap’s settlement to approve third party contracts like 1inch and Yearn vaults?
Second, the amounts in each interaction need to be hardcoded. The way solvers work is they simulate each interaction and instead of “deposit 100 SNX in yvSNX” it is actually “deposit xxxx SNXs in yvSNX”.
Our implementation moves tokens from the cowswap settlement to our Weiroll smart contract. There we send a weiroll execution which links the interactions. Basically, whatever the 1inch swap() call returns, we use it for the deposit() call in the yearn vault. Leaving no dust behind!

In the following image you can see an example of the settlement using Weiroll:

Weiroll being used inside CoW Swap
  • User sends WETH to CoW Swap settlement
  • Settlement sends WETH to TradeHandler (Weiroll powered contract)
    — TH converts WETH to SNX
    — TH deposits SNX in the Yearn vault
    — TH returns yvSNX to CoW Swap settlement
    — CoW Swap settlement returns yvSNX to the user

If you want to start using Weiroll you have two flavor's available,
a) js:
b) python:

PRO TIP: If you are running a safe multi-sign, you can use weiroll-py in conjunction with [ape-safe](


Another big regret of using hardcoded trade paths in our contracts is the lack of settlements between strategies. An example of what’s possible from now on. In prod, we have the following two strategies:

  • A DAI strategy selling CRV for more DAI
  • A yCRV strategy that claims 3CRV and buys CRV

These will generate the following orders:

  • SELL CRV for DAI
  • SELL 3CRV for CRV

Today, Yearn’s cowswap solver will see these two orders and expand them as the following:

  • SELL CRV for DAI
  • SELL DAI for CRV

and there we have our internal CoW. Lowering the LP fee for both strategies and increasing revenue.

Using Yearn internal liquidity

Having our own solver allows us to settle trade against internal liquidity from Yearn treasury. Yearn is doing YFI buybacks, why wouldn’t we do it through CoW Swap and CoWing?

Matching deposit() and witdrawals()

Deposits to Yearn vaults are very efficient gas wise. Depositor transfers tokens to the vault, there is some internal information updated and done.
For withdrawals, it depends. If the vault has a buffer, withdrawals are as cheap as deposits. If there is no buffer, the amount needs to be retrieved from strategies. If the amount requested is bigger than the buffer, the vault might unwind more than one position, costing the user a lot of gas.
Now that CoW Swap understands Yearn tokens, a depositor can create a USDC -> yvUSDC order and a withdrawer can create yvUSDC -> USDC and those two will be matched even when buffer is not present. Reducing user’s gas cost considerably for worst case scenarios.

Strategies’ rewards as CoW liquidity

At the moment, strategies are harvested by keepers based on certain parameters in each strategy. Yearn’s CoW Swap solver will use that information to provide liquidity for CoWs. If someone is buying CRV for DAI, and one of our strategies is ready to harvest, the solver will be able to work as a keeper and release the rewards to be cowed.


Dinobots, the team inside Yearn in charge of this project, is extremely excited to be working with the CoW Swap team. Helping CoW Swap understand more complex orders, converts CoW Swap from a token dex to an intent dex. Some of our test trades have up to 7 different interactions which would take a long time for a user to do. Imagine pushing a bit forward, and using CoW Swap to rebalance a portfolio. It feels like a Layer 1.5.



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