Bb 13b9, 5th inversion (G in the bass)
Also written as Bb13b9/G.
Notes, from the bass up
G (bass)A#DE#G#B
The same notes as Bb 13b9 (G, A#, D, E#, G# and B), rearranged so G is the lowest note. Use it to move between chords with smaller jumps across the keyboard.