**Traders assign an 86.5% probability to “No” on an outright first-round win in the 2026 French Socialist primary because the five-candidate field and voter distribution make a 50%+ majority unlikely.** The contest pits Raphaël Glucksmann (Place publique) against Olivier Faure (PS first secretary), Ségolène Royal, Jérôme Guedj, and Emmanuel Maurel in an electronic vote among roughly 140,000 registered participants drawn from the participating parties and paid supporters. Glucksmann leads in available surveys and party-affiliate sentiment, yet his support is concentrated among newer Place publique members while the larger PS contingent splits among Faure and others. A cyberattack extended first-round voting through October 11, but the structural fragmentation remains unchanged. With no candidate positioned to consolidate a majority in one round, the rules route the top two into the October 16–17 runoff. This setup, combined with the modest overall electorate and absence of a unifying frontrunner, underpins the strong trader consensus against an outright first-round victory.