Medium on Wednesday launched a new mobile story platform, Series, that lets users post photos and short-form text pieces that "unfold" over time. The best way to describe Series is basically to say it is Medium's version of Snapchat Stories.

There are two key differences from Snapchat Stories, though. Content doesn't expire after 24 hours and users can create as many different "series" as they want.

The new feature comes as Medium struggles to develop a clear business model. In January, CEO Ev Williams admitted that the company "didn't yet have the right solution to the big question of driving payment for quality content."

Series offers it a way to grow on mobile and provides an alternative to the lengthy, text-based pieces for which it is known. But it isn't clear how it will solve the business question.