Different bridges exist to support different operations. Two bridges currently exist on the xDai chain. Additional bridges and/or extensions may be deployed in the future.
xDai Bridge: Convert Dai to xDai and xDai to Dai
OmniBridge: Convert any other ERC20 tokens on Mainnet to equivalent ERC677 tokens on the xDai chain
An NFT Bridge is currently in active development.
The Optimistic Omnibridge is also in R&D as an option to provide a bridge for trustless transfers from xDai to Ethereum.
The bridge is a key element of xDai, allowing for fast interoperability between xDai and Ethereum. The bridge connects the networks and allows tokens to exist on both sides. To mint xDai, Dai is locked in the bridge contract and the equivalent amount of xDai is created on the xDai chain. In order to return this xDai to Dai, xDai is burned and Dai is unlocked.
Please check the Troubleshooting Section for common issues and resolutions.
The current limits are below. Note that these can be changed by a majority vote from the Governance Board.
Max Single Deposit
Transaction (Gas) Fees
variable, paid in Eth
paid in xDai
Transfer Fees (in addition to gas fees)
In response to increased usage and value locked in the xDai bridge, a proposal was introduced to extend security and decision making powers to a wider group of participants (governors).
The proposal was accepted, and governance by means of a multi-signature Gnosis Safe was put into place initially on the Ethereum side on 2 October, 2020. Once Gnosis Safe was deployed to xDai, updated governance was enacted on the xDai chain on 23 October, 2020.
At present there are 13 governors who are responsible for managing bridge operations on both sides of the bridge (contracts are deployed on the Ethereum and xDai side). 7/13 signatures are required to approve any management proposal. Operations may include:
Bridge contract updates.
Contract parameters updates such as bridge limits, finality threshold, gas price fallback etc.
Bridge validator parameter updates like changing the validators set or signatures threshold.
All actions are managed through Gnosis Safe accounts, one on the Ethereum mainnet for Ethereum contract side operations and one on xDai for xDai contract operations.
Gnosis Safe contract on Ethereum: https://gnosis-safe.io/app/#/safes/0x42F38ec5A75acCEc50054671233dfAC9C0E7A3F6/settings
Gnosis Safe contract on xDai: https://xdai.gnosis-safe.io/app/#/safes/0x7a48Dac683DA91e4faa5aB13D91AB5fd170875bd/settings
There are currently 5 bridge validators, and 3/5 signatures are required for bridge transactions. The validator set can be updated by the Governance Board.
The process requires several steps on the xDai chain.
Oracles send confirmations of the transaction to the bridge contract.
After receiving the required number of confirmations, the bridge contract sends a request to the Block Reward contract to schedule emission (minting) of new xDai (the same denomination as requested in the bridge transaction).
The Block Reward contract is invoked by the xDai network validator during the last step of block verification, and account balances are updated in the Block Reward contract.
No, anyone can pay the fees to process the claim transaction and receive DAI, but the DAI will always be sent to the account set as the receiver in the initial originating request. This functionality opens the door for projects or other entities to pay for gas fees/subsidize the claims on Ethereum.
No. The amount will remain locked in the contract until you decide to claim it. If gas prices are high, you may want to wait to execute the claim transaction when prices are more in your favor. For more on dealing with high gas fees for claims, see this troubleshooting question.
If you have an unclaimed amount, you will see a message once you connect your web3 wallet to the application.
Click on the History button to see your transactions, then click the Claim button in the history section to claim the transaction. You will need Eth to complete your claim.
No, this is not possible. When the first transaction is complete, the requested amount of xDai is burned on the xDai chain. If you want to return the amount back to the xDai chain, you must finalize the transfer (claim) on Ethereum and then send back to the xDai chain via the bridge to mint xDai once again.
Once a quorum of confirmations is reached, the transaction is executed and the remaining confirmations are not required. This saves resources, and creates an easy visual record to see which validators confirmed for any given tx.
Successful transactions are recorded with Status "Success", and additional validator confirmations, which are not needed, are either marked as 'Failed' or 'Not required' depending on the processing order.
Please see the OmniBridge documentation at https://docs.tokenbridge.net/eth-xdai-amb-bridge/multi-token-extension for additional details.
You can find a current list on BlockScout at https://blockscout.com/xdai/mainnet/bridged-tokens
Use the AMB Live Monitoring application located at https://alm-xdai.herokuapp.com/. You can enter a transaction originating from either side of the bridge. More information on various ALM transition states is available here.
No, OmniBridge is an extension (similar to a DApp) unrelated to chain consensus and it uses a separate set of validators and governors. Currently, there is a 4/7 signature requirement for Omnibridge transfers.
This can vary by token. The default setting when a token is first bridged is 1, but this can be changed by bridge governance. To check the minimum for a particular token, query the
minPerTx method of the omnibridge mediator contract.
Enter the bridged contract address into the
minPerTx field. Convert from wei using http://eth-converter.com/
Yes you can. Instructions.
Yes, it is possible, you will need to collect the message and the oracles' signatures. A button is built into the ALM for this functionality.
Yes, attempts are made to replace transactions with a higher gas price after 20 minutes. This occurs if it receives a price provided by the gas price oracle, and is repeated every 20 minutes until the transaction is successful.
Generally, the MetaMask gas limit estimates are high for OmniBridge tokens. In the following example, the gas limit was 1,036,275 but the gas spent for the execution was 208,805, 5 times lower than estimated.
Each token has unique parameters, and it is not possible to provide an accurate estimate before the tx is sent to the bridge oracles. Here are a few examples to provide an idea of the gas costs when transferring tokens from xDai to Ethereum*.
Min Gas to Execute
Max Gas to Execute
When confirming a transfer, you will see a note with information about a claim transfer. This is a semi-accurate estimate of cost (it is a hardcoded value).
You always have the option to process the first tx on xDai, then wait until gas prices are lower on Ethereum to execute the 2nd claim transaction.
Yes, you will need that much in your wallet to initiate the claim transaction. However, only the amount used for gas fees will actually be deducted from your balance.
With the example in the question above, the MetaMask estimate tx fee was 0.109 ETH/$200 worth of ETH at the time. The user needed to have that amount to start the tx, but the final cost was only 0.0218 ETH/$40. It is also useful to check the current gas price and possibly adjust your gas price (amount you are willing to pay per unit of gas) but DO NOT adjust the gas limit (the max amount of gas spent for the claim).
Unfortunately not, once you have started the transfer process it is non-reversible. The only way to complete is to claim the token on Ethereum. If too expensive, you can wait until gas fees come down. There is not a time limit to claim the transaction.
Yes, it is possible to use BlockScout and Etherscan to interact with the contracts and submit manually, or if you are familiar with the contract interaction through a Web3 provider, you can importing the contract's ABI to your application. This post details how.
Honeyswap is a popular application running on xDai and utilizing bridge functionality. They have a forum at https://forum.1hive.org/ with tons of info, a Discord and an FAQ that covers basics about bridging, xDai and more. Please bring any related questions to them.