Asset Hub Migration - XCM FAQ

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Asset Hub Migration - XCM FAQ

The Asset Hub Migration of both, Kusama & Polkadot networks is currently planned for later this year. If you’re unsure of what the AHM is or why the team is planning this, then check out this thread here.

What is this topic for?

This topic will be for all AHM FAQ’s relating to XCM. We’ve pre-filled some FAQ’s below, however if your questions is not answered by any of these, please feel free to comment below and ask away.

FAQ’s

How will XCM reserves be impacted by this migration?

  • They will be migrated to Asset Hub: Para A’s sovereign account balance on relay (its DOT reserve) will be migrated to (summed together with) Para A’s sovereign account balance on Asset Hub. Para A must switch its reserve location configuration to point to Asset Hub.

Will the reserve location be automatically changed to Asset Hub as part of the migration?

  • No, this won’t be done automatically. All Parachains will need to update their reserve locations in their XCM config for DOT to Asset Hub instead of the Relay Chain. Here’s a guide explaining how-to and a tool in order to test if the change was successful.

Can I do the change before the Asset Hub Migration?

  • Yes. You can do this change before the rest of the migration since the Asset Hub is already suitable to be a DOT reserve. The only important thing to note is that staking and governance will still be on the Relay Chain, so you’ll probably still be using it. That’s fine, you can move the DOT between your chain and the Relay using the Asset Hub as a reserve.

Will Asset Hub become the only reserve for DOT?

  • Any system chain can act as a reserve for DOT. This is the case now and the same holds after this migration. This even includes the post-migration relay chain (for as long as it still has balances and allows DOT transfers).

  • In practice, we recommend parachains to configure Asset Hub as the only reserve location. All DOT cross-chain transfers will have to go through Asset Hub, but this way they don’t need to worry or care about other reserve accounts.

  • E.g. Para A to Collectives DOT transfer would be: ParaA–ReserveWithdraw–>AH–Teleport–>Collectives

  • Looks the same for any other system chain instead of Collectives.

How will this impact delivery fees on the relay chain?

  • Parachains should not be doing any transactions on the relay chain post-migration. Nothing changes on relay chain fees, as long as it still has balances, DOT will be charged for all types of fees. If someone needs DOT on the relay chain they would have to teleport it in from Asset Hub, but apart from registering a parachain, there should be no use case where you would need to send transfers on the relay chain.

Will the DOT on the relay chain sovereign address be automatically transferred to the parachain sovereign address on AH after migration?

  • Yes, all account balances will be transferred over automatically.

The public keys of the relay chain sovereign address and AH sovereign address for parachains are different. Could this cause DOT to be transferred to the wrong address during migration?

  • No, this will not cause any issues. While funds can be recovered to the correct address on AH through a mechanism that proves ownership, it’s recommended to teleport the funds before migration to avoid this process. Teleportation will require your parachain’s sovereign account, governed by governance or sudo.

For parachains using derivative addresses of sovereign addresses, will they face similar issues during migration?

  • This issue is resolved similarly to the above. However, teleporting these funds before migration is also recommended.

What happens to DOT in crowdloans, staking, and other locked assets during the migration?

  • Initially, crowdloan funds will remain on the relay chain, and existing processes to withdraw, refund, or dissolve will continue to function normally. A mechanism to directly refund these funds to AH is planned for release later this year.

After the migration, can XCM between parachains still be done through HRMP?

  • Yes, there should be no change for this setup.

Do Parachains that use ParentAsSuperuser need to make any changes?

Yes, Parachains that use and rely on ParentAsSuperuser (where the relay chain can gain root) should adjust their XCM configuration to also trust AssetHubLocation (This is due to the OpenGov migration) and / or allow unpaid execution for AH.

Whilst it is strongly recommended to update this, this is not critical and OpenGov should still perform AssetHub → Over RelayChain → Parachain root calls.

Please see the example below

- // Superuser converter for the Relay-chain (Parent) location. This will allow it to issue a
- // transaction from the Root origin.
- ParentAsSuperuser<RuntimeOrigin>,
+ // AssetHub or Relay can execute as root (based on: https://github.com/polkadot-fellows/runtimes/issues/651).
+ // This will allow them to issue a transaction from the Root origin.
+ xcm_builder::LocationAsSuperuser<(Equals<RelayChainLocation>, Equals<AssetHubLocation>), RuntimeOrigin>,
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