The little wooden rascal is the official part of the MCU canon.
'I Am Groot' premiere has established Groot's place in the Marvel Cinematic Universe timeline, but things are not necessarily as simple as you might imagine. It turns out that the five shorts take place in different time periods across the timeline.
Particularly, episode 1, titled 'Groot's First Steps', takes place between 'Guardians of the Galaxy' Vol. and Vol. 2, while the rest of the episodes occur after Vol. 2.
Such a discrepancy comes due to the fact that Groot is growing over the course of the MCU phases. In the Infinity Saga, he was a teenager; but Groot's solo show covers different stages of his life. The 'Guardians of the Galaxy' director James Gunn has hinted that the upcoming third movie might provide viewers with a glimpse into Groot's adulthood.
According to MCU producer Brad Winderbaum, the events of 'I Am Groot' take place "between the end of Guardians 2 and before the tag scene in 'Guardians 2'." Basically, four episodes of 'I Am Groot' take place just before the final post-credits scene of the second movie.
Right after 'I Am Groot', according to the updated MCU timeline, goes 'Avengers: Age of Ultron', 'Ant-Man' and 'Captain America: Civil War'. The Groot series are a nice flashback to the times when events in the MCU were… a bit less dramatic. Essentially, 'I Am Groot' is not directly related to the ongoing Multiverse Saga in the MCU.
With the first five shorts premiering on Disney Plus on Wednesday, there are five more to come: there is a possibility they would be placed in a different part of the MCU timeline.