I could not find any datasheets on this either when I wondered the same thing a few months ago, but I'm almost positive it is only 1Gb. I tried to connect an MS-425 using the MA-SFP-1GB-TX to an older 100mb HP Procurve switch (in a lab) and would not detect a link (no link lights on either switch). I tried 2 different MA-SFP-1GB-TX to make sure and same scenario on both. (Also tried the Cisco GLC-T with the same result) I then connected the MS-425 to both a new HP 1GB Procurve and also an MS250 and worked without any issues.