Currently it's only on the beta server, so you have to use a special syntax to access it. Basically if your current photo gallery URL is:
Then to access it via the beta server you use:
As an example, try this link which is a real link to a photo gallery that works:
Using the above link syntax should show any existing photo galleries you have using the new style. For more discussion and to provide feedback about this new photo gallery format, please see use this forum thread.