Generally, if the total reportable income is less than $12K for the entire tax year, then no tax return needs to be filed. However, if that stipend was reported on a 1099-MISC and was more than $400, a tax return "should" be filed so the IRS doesn't assume it's self-employment income.
With self-employment income, if you made more than $400 in the tax year, then you are "required" to file a return and report it, since you have to pay self-employment taxes on any amount that exceeds $400.
