Last month, along with the switch back to an algorithmically-generated News Feed, Facebook also announced some important changes to feed stories and the feed APIs. Those changes are going live tonight, Facebook just said.

Most visibly, Facebook is reducing the number of images that can appear in feed stories by default from three to one. Instead, Facebook is now showing a “See More” link that will allow users to expand all three images in line. We reported a couple months ago that Facebook was telling developers to start using just one image because it wants app feed stories to look less “spammy” and more like Facebook’s own feed stories. However, while most Facebook feed stories only include one image, we assume its photo stories will still include three.

Until now, apps have been allowed to publish up to three images in feed stories, with most developers choosing the maximum allowable size under the current specs in order to get more clicks and attention in the stream. Starting tonight, the maximum size of images in the stream will also be reduced to 90×90 pixels.

Here’s how the old feed images looked:

And here’s the new feed images format:

These are non-breaking changes, meaning only the first image will be displayed if developers change nothing. In addition, Facebook says it will only “display approximately the first 300 characters of text” in feed stories.

Older feed APIs are also being deprecated on December 20th. A couple weeks ago, Facebook reduced the number of action links displayed for app feed stories down to one.