Bb 13b9, 4th inversion (B in the bass)
Also written as Bb13b9/B.
Notes, from the bass up
B (bass)GA#DE#G#
The same notes as Bb 13b9 (B, G, A#, D, E# and G#), rearranged so B is the lowest note. Use it to move between chords with smaller jumps across the keyboard.