Toy manufacturer Hasbro has announced a crossover of some type between its Transformers line and Marvel Comics' Uncanny X-Men some time in 2021 as part of its Transformers Collaborative line, as announced on the official Transformers Facebook page.
A teaser image posted on Hasbro's Facebook page shows the X-Men's iconic Blackbird jet alongside the Autobots logo, and the caption "Guess what's neXt?" with a stylized capital X.
Though Hasbro's simple teaser doesn't indicate anything about what shape the Transformers/X-Men crossover might take, be it a comic book, toy line, or something else, the 'Transformers Collaborative' branding on the teaser may offer some ideas. Transformers Collaborative is a Hasbro line in which characters from Transformers crossover with other franchises, with previous iterations including both toys and comic books.