First, you can see what’s changed with the new impOS release here: https://electricimp.com/docs/releasenotes/releases/release36/
You can use imp.getsoftwareversion() to determine which version a given device is running. For example, I add the following to all my development code and call it early:
function bootMessage() {
local a = split(imp.getsoftwareversion(), "-");
server.log("impOS version " + a[2]);
local i = imp.net.info();
local w = i.interface[i.active];
local s = ("connectedssid" in w) ? w.connectedssid : w.ssid;
local t = (w.type == "wifi") ? "Connected by WiFi on SSID \"" + s + "\"" : "Ethernet";
server.log(t + " with IP address " + i.ipv4.address);
}