what version software do I need

Noel Dastugue

I bought a  Flex 6400    2 years ago but due to my business I'm just getting on the air with it. ( retired again)  I'm running smartSDR V2.1.33 .. I would like a surjection as to what software I should be running .. Thanks... 

WX7Y

You can go up to the latest version of V2 for free If you want to upgrade to the Latest version and features then it will probably cost you $200. 00 for Version 3. 
Go here for the new features https://www.flexradio.com/ssdr-for-windows/

Bret

Ryan - K4BFH

2.6.1 is the newest of the 2.x which would be free for you. To upgrade to 3.x is 200.00 USD.
https://www.flexradio.com/downloads/ click  Smart SDR for windows 2.x to download the newest version.

John KB4DU

I admire your patience. I would not be able to wait that long to use a new radio.

I suggest upgrading to either 2.5 or 2.6 ( the no additional charge versions) until getting familiar with the radio as you use it at your station. After gaining some experience, it will be easier to determine if the V3 changes are useful. Many on the list here have decided to stay with 2.? because some of the changes to the software are detrimental to their particular operating style.

The radio can be returned to a previous version at any time if 2.6 doesn't perform as you need.