keep something, stay, etc. under wraps
stay under wraps
To remain secret; to not be disclosed to anyone. I think it's best that this stays under wraps until we can determine what impact it will have on the public.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
keep something, stay, etc. under ˈwraps(informal) keep something, stay, etc. secret or hidden: These letters have lain under wraps since the 1960s. ♢ Next year’s event is still being kept under wraps.
Farlex Partner Idioms Dictionary © Farlex 2017