In the Advanced Prompting study, a two-stage IV model is fit in which a user's realized exposure to the Suggest condition (operationalized as the share of engaged minutes under Suggest) is instrumented by the user's earliest project default condition (randomized assignment used as an encouragement). With limited early data, the preliminary point estimate for the effect of exposure on acceptance is small and not statistically distinguishable from zero under HC3 inference. The authors present this only as a sanity check on the instrumentation, with fuller estimates reported in the camera-ready.