I understand that, however System.Threading.dll is not installed by default. Its included in Reactive Extensions as a back port of the threading and task classes to .net 3.5. I want to support .net 3.5 in a build and want to make it easy for clients by merging this in. No option for this? I'd think you could have some override? Can I ILMerge after SmartAssembly, will that cause issues with Obfuscation?