Existing beta cluster wikis deployed on the wmflabs.org domain are not affected. This work will help us test the cross-domain cookie behaviour[1], and provide the playground for the upcoming third-party cookie phase-out work [2].

Consider using one of these domains if your work involves cross-domain tasks, such as handling authentication issues. Browsers tend to enforce stricter rules on user activities that go beyond the beta.wmflabs.org cookie security boundary.