Is the preview in Knapsack identical to what's in the production app?

Yes! As part of implementation, we ensure the renderer(s) used by your Knapsack workspace match the renderer(s) used in your production application(s). This means that your design system code is only rendered by the production application (what users experience) and by Knapsack (used for collaboration, experimentation, and testing). 

As a result, teams are able to capture the opportunity presented by system-level testing without the overhead required to create and maintain production-quality endpoints (and supporting infrastructure).