Is Grok Imagine Private really Private?

Since June 4th, Grok Imagine has been performing moderation. However, there are some puzzling aspects.

• The output image format when generated with the 1K setting has changed from PNG to JPEG.

• The metadata now includes "Signature." (it wasn't included before).

These specifications are the same as official Grok. (Although official Grok uses JPG instead of JPEG.)

Furthermore, the message displayed when moderation occurs reads: "Please try again with an image generated using Grok Imagine Image models."

Doesn't this mean that the metadata of images generated with Grok Imagine Private is retained and exists on the server?

The xAI FAQ Security page states, "When ZDR is enabled for your team, your prompts, completions, and associated metadata are processed in real time but never persisted to our servers; once a response is delivered, no record of the exchange remains."

I understand that Grok Imagine "Private" means it works with ZDR, but is that really the case?