I can't figure out how to try this thing. The closest I got was this sentence:
"To get started with Imagen 2 on Vertex AI, find our documentation or reach out to your Google Cloud account representative to join the Trusted Tester Program."
It also includes a link to the TTP form, although the form itself seems to make no reference to Imagen being part of the program anymore, confusingly. (Instead indicating that Imagen is GA.)