So if there is no link for batch 4 firmware where did you find the info?
That screenshot is from the bitmain firmware site; the file descriptions are:
S9 firmware-20160608-650M
s9firmware-20160608-600M,12.93T
s9 firmware -20160608-550M,11.85T
The last line showed up most recently. Like I said - speculation, but it is pretty suggestive.