With the tested format, you had to swipe and tap through your feed.
But everyone can relax. "This was caused by a bug and we quickly rolled it back", an Instagram spokesperson told the site.
Instagram has reversed the update as a result of the slew of complaints.
Bigger picture: Tech companies often push out unpopular updates since they think people will use their apps more, according to Recode. And had it only been the small test envisioned by Instagram, no one probably would have even heard about it.
Mosseri confirmed that the update should be cleared for everyone, and to just restart your app if you were still seeing it. That still didn't stop the company from unintentionally pushing out a major update that screwed up users' feeds this morning.
Instagram user Elise Michelle called it: "By far the worst update in Instagram history".
Lots of people took to Twitter to vent their frustration of the new adjustment.
"Always trying new ideas, usually with a much smaller number of people", he said.
It's likely - having put the time into developing this "feature" - that Instagram does intend to make horizontal scrolling an option in future, if not the default interface.
A test change to Instagram got out of control. Stop this chaos and bring back the chronological news feed. "We apologise for the confusion", reads the tweet.
Users across the globe are reporting the app switched within the last hour.
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