There is a statement in the closing credits: "No raccoon or tree creatures were harmed during the making of this movie. However the same cannot be said for the handlers of the raccoon and tree creatures."
Zardu Hasselfrau's Guardians of the Galaxy: Inferno (2017) song is heard in the closing credits. At the end of the credits the disembodied head of Zardu Hasselfrau states: "In times of hardship, just remember: We are Groot!" just as in the video.
Several credits in the closing credits read "I am Groot" before flickering and changing to the actual credit. Additionally, "I am Groot" appears in the stars twice, as a constellation and as a "You Are Here" location. Also, in the disclaimer that normally states no animals were harmed. It is replaced with "I am Groot." Before it changes to "No raccoons or tree creatures were harmed during the making of this feature. The same cannot be said for the handlers of said raccoons and tree creatures."
Cosmo the dog, Howard the Duck and the Grandmaster (a cosmic being from Thor: Ragnarok (2017)) are seen in the credits
SPOILER: There are 5 scenes in the closing credits:
The opening credits are of Groot dancing to Star-Lord's music, during a battle between the Guardians and a space monster (seen in the background).
At the end of the closing credits, Star-Lord picks up his Walkman and walks off, with the music coming to an end when that happens.
Richard Christy is credited as "Down There!"
There is a statement at the start of the closing credits: "The Guardians of the Galaxy will return." Their next appearance is in Avengers: Infinity War (2018).
The costume designers credits is accompanied by an image of Yondu with his new fin.