As reported by TechCrunch, the new option - called 'Promoted Trend Spotlight Ads' - will allow for either still images or GIFs, and will appear the first two times a user visits the Explore tab each day, before it reverts back to the regular Explore layout.
The ads are definitely hard to ignore, which could help drive appeal, and while these will be a high-end offering, it is interesting to look at how Twitter is seeking to monetize their various surfaces - and how users then respond to the interruption.
Indeed, it was only last month when Twitter announced new changes to the Explore tab, which include topic-based listings aligned with each users' interests.
The new ad type will somewhat negate these changes, at least in terms of using the tab for its intended purpose - but as noted, they will be valuable for big brands, who are always keen to find ways to boost exposure to the platform's millions of users.
It doesn't seem like a major, disruptive change, and it probably won't be a significant negative, which could make it a great opportunity for Twitter to drive more ad dollars without annoying people too much. It will, however, be expensive. If you're hoping to get in on the action, the ads are considered an extension of Promoted Trends, which reportedly cost from $250k per day up, dependent on the day you choose.
You'd expect that a full promoted image/GIF trend would be higher than this, so yeah, probably not in the ballpark of most digital ad budgets.
At present, the new option is only in test mode, with no full rollout planned at this stage.