I'm somewhat surprised it didn't come up in the interview. I don't think you should tell them in your thank you note. Do you think your stutter isn't noticeable? Why do you think you should tell them? ​ I don't think you should make a big deal about it. I would only tell them in the interview, let them bring it up. I've had previous employers tell me they don't even consider my stutter a disability (somewhat validating and also invalidating? mine has gotten more moderate over the years). But if you're already going in for an interview, they will probably be able to figure it out, especially if it's in person. If it's over the phone, they might think the line got disconnected or you're breaking up (though this has never made sense to me), at which point you can tell them. Some potential employers will ask you how you will be able to perform the work required for the job/how your stutter will impact your work. Just have a good answer for them. Do not throw yourself under the bus! Keep your responses positive. For example, your speech may be more severe when you first start, but it will improve as you become more comfortable in the position.