There used to be question for "this money was earned as part of a fellowship." (Was it removed, or did you miss it?) Hobby would be an acceptable choice in this situation. You owe income tax, but because this was part of your education provided through your own university, it is not considered "work", so it is not "income earned from working" and is not subject to self-employment tax. Keep records documenting the fellowship because the IRS may send an automatic letter asking you to pay SE tax and you will want to have proof ready to include with your response.