---
schema_version: "secwatch.filing_event.v1"
accession: "0001193125-25-162552"
form_type: "8-K"
ticker: "MCRB"
cik: "0001609809"
company_name: "Seres Therapeutics, Inc."
filed_at: "2025-07-22T23:59:59+00:00"
generated_at: "2026-05-18T04:18:25.412935+00:00"
event_type: "leadership"
sentiment: "neutral"
materiality_score: 0.75
calibrated_materiality_score: 0.75
confidence: "high"
source: SEC EDGAR
---

# Seres Therapeutics CEO Eric Shaff resigns; CFO and CLO appointed as Co-CEOs effective Aug 1, 2025

## Summary
- Eric Shaff resigns as President and CEO effective July 31, 2025; remains on Board as Class I director.
- Marella Thorell (EVP/CFO) and Thomas DesRosier (EVP/CLO) appointed Co-CEOs and Co-Presidents effective Aug 1, 2025.
- Shaff to receive prorated 2025 bonus; Board may accelerate payment if a strategic transaction closes before year-end.
- Thorell and DesRosier each receive $500,000 appointment bonus: one-third on Aug 1, 2025, balance on Jan 1, 2026 subject to retention.

## SEC filing metadata
- accession: 0001193125-25-162552
- form_type: 8-K
- ticker: MCRB
- cik: 0001609809
- company_name: Seres Therapeutics, Inc.
- filed_at: 2025-07-22T23:59:59+00:00
- event_type: leadership
- sentiment: neutral
- materiality_score: 0.75
- calibrated_materiality_score: 0.75
- confidence: high
- sec_items: 5.02
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1609809/000119312525162552/0001193125-25-162552-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1609809/000119312525162552/d40383d8k.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001193125-25-162552
- JSON: https://secwatch.observer/filing/0001193125-25-162552.json
- Plain text: https://secwatch.observer/filing/0001193125-25-162552.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.