Say I make a static class like following with an extension method:

public static class MyStaticExtensionClass
{
    private static readonly Dictionary<int, SomeClass> AlgoMgmtDict
        = new Dictionary<int, SomeClass>();

    public static OutputClass ToOutput(this InputClass input)
    {
        // clears up the dict
        // does some kind of transform over the input class
        // return an OutputClass object
    }    
}

In a multi user system, will the state management dictionary fail to provide correct values for the transform algorithm? Will a regular class be a better design or shoving the Dictionary inside the method a better design?