As universities have become more reliant on philanthropies for research funding, new models for university-philanthropy collaboration have emerged. These alliances operate as social contracts in which universities provide intellectual capital, legitimacy, and access to expertise, while the philanthropic organizations provide resources beyond funding and a vision for impact through innovation. Through their partnership efforts, these new university-philanthropy alliances enable research at a larger scale and with greater agility than the parties might achieve working separately. This qualitative case study examines the motivation, modality, evolution, and complexities of three unique university-philanthropy research alliances in the United States: the Allen Institute for AI with the University of Washington; the Chan-Zuckerberg Biohub with the University of California, San Francisco; and the Wyss Institute with Harvard University. This study reveals three key findings. First, these alliances are driven by normative motivations, a shared commitment to societal impact, and pragmatic needs for resource complementarities. Second, relational contracts, characterized by implicit factors and trust, play a more significant role in shaping these partnerships than explicit legal agreements. Third, structural adaptations and cultural transpositions create fluid and flexible organizational boundaries, distinguishing these partnerships from other forms of research collaborations. By examining these alliances, this study provides critical insights for university leaders and philanthropists seeking to establish or refine their own partnerships. It also contributes to broader discussions on the evolving role of philanthropy in higher education, the social contracts between universities and their research sponsors, and the strategic pursuit of new research sponsorship models.