When should you pick GraphQL over REST for internal APIs?

We've pretty much only used REST for our internal service talk, and hey, it's done the job. But lately, with some newer services asking for more complicated data stuff and filtering, I'm kinda thinking GraphQL could be better. Especially when a frontend client (or even just another internal service playing the 'client' role) has to grab info from a bunch of backend services and only needs particular bits. So, is anyone actually using GraphQL internally and seeing it's better than REST for specific situations? What have been the ups and downs you've hit, besides just learning how to use it?