Preview build
An early Dynamics 365 release wave build available roughly six weeks before general availability — for sandbox testing against the upcoming version.
A preview build is an early version of a Dynamics 365 release wave (or platform update) made available roughly six weeks before general availability. Customers spin up a preview sandbox from their admin centre, install their extensions and integrations against it, run their regression suite, and certify their AppSource apps against the upcoming version. The preview window is the canonical opportunity to catch breaking changes before they affect production. AppSource ISVs are expected to validate compatibility during preview; per-tenant extension owners must recompile and republish before the production update window. Skipping preview testing routinely causes preventable issues at wave updates; investing the few hours of preview validation prevents days of production firefighting.