Seres Therapeutics MCRB Institutional Ownership

Updated Oct 10, 2026

Seres Therapeutics, Inc. (NASDAQ:MCRB) was held by 37 institutional investors that filed 13F reports for the quarter ended June 30, 2026.

• Collectively, these holders controlled 23.14% of Seres Therapeutics' outstanding shares in Q2 2026, down from 24.04% in Q1 2026.
• Total shares held in Seres Therapeutics fell 1.39% versus Q1 2026, while the number of holders rose 15.62% versus Q2 2025.
• Looking at the 37 holders of MCRB individually, 16 added to their positions, 12 reduced their stakes and 9 left their positions unchanged.
• Combined, institutional investors held 2.27Mn shares of MCRB as of Q2 2026, down 32.06K from the prior quarter and down 2.7K from a year earlier.
• As of June 30, 2026, the biggest holder of Seres Therapeutics was Flagship Pioneering, LLC with 1.16Mn shares, or 11.76% of shares outstanding.
• Among holders that already owned Seres Therapeutics, the biggest buyers in Q2 2026 were Marshall Wace, LLP (+32.71K shares), Vanguard Fiduciary Trust Co (+9.04K shares), BlackRock, Inc. (+8.97K shares), Geode Capital Management, LLC (+5.14K shares) and Group One Trading LLC (+2.89K shares).
• The largest position reductions in MCRB for Q2 2026 were by Susquehanna International Group, LLP (-47.01K shares), American Century Companies Inc (-34K shares), Vontobel Holding Ltd. (-15.49K shares), Morgan Stanley (-9.56K shares) and UBS Group AG (-6.55K shares).
• Business Quant data shows the 10 biggest positions in Seres Therapeutics as of Q2 2026 were held by Flagship Pioneering, LLC (1.16Mn shares), Vanguard Capital Management LLC (287.78K shares), Marshall Wace, LLP (172.25K shares), Vontobel Holding Ltd. (122.97K shares), BlackRock, Inc. (111K shares), Geode Capital Management, LLC (79.97K shares), Susquehanna International Group, LLP (58.33K shares), Vanguard Fiduciary Trust Co (48.69K shares), State Street Corp (33.9K shares) and Lion Point Capital, LP (31.57K shares).