You can choose your preferred version by logging into the user area and scrolling down to Server Settings > Server Type. You will then see the available Server Platforms
We have decided not to automatically force the update for all customers as many are still using the old style of Authhash to get listed on the SHOUTcast YP.
If you are not listed on the SHOUTcast YP then you can use an version.
If you have an old style Authhash, which is a string of letters and numbers only (e.g gM7nnd9TFjP94yE7EdJr), then use V2.5
If you have a new style Authhash, which contains dashes along with letters and numbers (e.g hNw3RgDg-W66u-pm8S-YAh7-aHGs8JWCBg4V), then use V2.6
Note: The authhashes above are randomly generated and will not work. They are intended only as examples to show the difference between the new and old formats.