The latest Telerik UI for ASP.NET AJAX version is Q2 2015 SP2 (2015.2 826).
Note that since you are using a Classic version of our controls, migrating to the AJAX version would require some additional efforts. You may check the following help article for reference - Migrating From RadTabStrip Classic to RadTabStrip for ASP.NET Ajax
. In addition, you may need to perform migration for other controls as well, as described in similar help articles accordingly.
And as a side note I would like to mention that Classic controls versions are no longer supported as pointed in the Telerik Support Lifecycle Policy
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