If trombone music is in the key of G flat what would the key be for a B flat instrument?

If you play a standard B flat Trombone and you read in bass clef, G flat is in 5th position. That applies to G flat below the stave, in the stave and above the stave however the one above the stave can also be played in a sharp 3rd position. Which means you bring your slide up a bit more towards you. I don't know about trombones in other keys. Hope that was of some help.