In a T4 template the executing assembly is not yours but one from the T4 engine.

To access types from your assemblies, you have to perform the following steps:

1. Add a reference to your assembly to the template. Put that at the top of it:

   <#@ assembly name="$(SolutionDir)<Project>\bin\Debug\<Project>.dll" #>

2. Import the namespace of your assembly. Put that somewhere below the previous line:

   <#@ import namespace="<Project>.<Namespace>" #>

3. To access the types in this assembly, pick one of them and get the assembly from it:

   var assembly = typeof(<Type in assembly>).Assembly;var types = assembly.GetTypes()                    .Where(t => String.Equals(                        t.Namespace,                        "RepoLib.Rts.Web.Plugins.Profiler.Models",                        StringComparison.Ordinal))                    .ToArray();

T4 assembly