**Strong existing collaboration without merger signals supports the 89.5% market-implied probability against a 2026 Merck-Moderna acquisition announcement.** The companies have maintained a decade-long partnership, formalized in 2016 and expanded with a $250 million milestone in 2022, focused on co-developing the personalized mRNA cancer vaccine intismeran autogene (mRNA-4157/V940). This 50/50 economics arrangement recently delivered a landmark Phase 3 success in the INTerpath-001 trial for resected high-risk melanoma, with statistically significant gains in recurrence-free survival and distant metastasis-free survival versus Keytruda alone—prompting Moderna’s shares to surge over 90% in August 2026 and analysts to project multi-billion-dollar peak sales potential. Merck has instead pursued other oncology deals, including the $6.7 billion Terns Pharmaceuticals acquisition (announced March 2026) and a $400 million upfront licensing deal for a KRAS G12D inhibitor, while Moderna independently raised $2.6 billion via convertible notes to fund oncology expansion and hired a COO to scale that business. No regulatory filings, activist pressure, or credible rumors point to full ownership change; the firms continue executing as partners on this asset amid separate capital-raising and pipeline strategies. Upcoming catalysts include detailed Phase 3 data at ESMO in late October 2026 and potential regulatory discussions, which could further validate the collaboration without shifting M&A odds. The 89.5% “No” reflects trader consensus that the established joint development framework and independent corporate actions make a transformative deal unlikely by year-end.