Playground and Unity Spark are different starting points. Here's the quick version of what Google and Unity announced. The full video includes the complete Spark demo and my questions about the first version.
Spark demo footage supplied by Unity; pre-release version, with my commentary.
Full breakdown: https://youtu.be/ESr-JxuIQg8 (also linked as this Short's related video)
Unity Spark: https://unity.com/spark
Google Playground: https://playground.google.com
Roblox Assistant: https://create.roblox.com/docs/ai/accelerated-workflows
This is an announcement discussion, not a hands-on review. Spark beta availability and features can change.