In recent years, one has observed the emergence of new public policy tools for innovation: prizes platforms. The objective of this article is to better understand the contributions of prizes as an instrument of innovation policy. More precisely we study the extent to which prizes allows political actors to implement a more open political process to stimulate and support innovation. Through a qualitative study we examine the functioning of two public prizes platforms: in the United States (Challenge.Gov) and in Europe (the European Commission prizes). If the use of prizes remains limited compared to traditional innovation policy tools, our conclusions confirm the implementation of – partially – open innovation processes by public actors, through prizes. To better understand the current challenges, we propose in the discussion to refer to the concept of tentative governance, reflecting the need to take into account the dimensions of both inclusiveness and uncertainty.