The Iris API isn't distributed separately yet, but it has a much better stability guarantee than referencing internal Iris classes. In the future we plan to do reorganization and repackaging which might break things in your mod.

The methods available in the following class should be sufficient: https://github.com/IrisShaders/Iris/blob/41721a53dde15698bf03c6763475c62978105e7c/src/main/java/net/irisshaders/iris/api/v0/IrisApi.java

If/when you've released a new update using the API, we'll make sure to mark older versions of Puzzle as incompatible on our side to avoid any potential issues once we do choose to do internal refactors.

Thanks!