Only some lLeaked images from China so far, but SS-38 has been revealed to be the "Gen1" styled Optimus Prime from the Bumblebee Movie... specifically noting itself as being the truck that we saw on the Golden Gate Bridge in the Movie.
Maybe this toy was being held back from its official reveal until after the Bumblebee movie started in most countries (this week), as it could look like a spoiler... if it made people think that Optimus Prime had a role on Earth during the movie.
The cover of the instructions were leaked first... followed by this photo of the toy in robot mode within a couple hours... and then a photo of the back of the box within half a day of that.