Anonymized engagement summary: consolidating two Microsoft 365 GCC High tenants into one after an acquisition, for a defense technology company (2026)
Anonymized engagement summaryDefense technology company · 2026
Opening answer. In 2026 EPC Group was engaged by a defense technology company to consolidate two source Microsoft 365 GCC High tenants into one destination GCC High tenant following an acquisition, for a baseline of up to 300 users. The production migration covers Exchange Online, SharePoint Online, OneDrive for Business and in-scope Power Automate workflows. It runs in phases over about eleven weeks: readiness and a pilot, critical-user waves, remaining waves, then close-out with evidence and stabilization. Parallel workstreams cover:
- the first stage of a file-services move
- permission and identity-mapping re-architecture
- a hybrid identity exit roadmap
- endpoint, Intune, Defender and mobile readiness
- Power Automate remediation
- governance readiness validation
Everyone who touches the client's GCC High data is a U.S. person working under EPC Group's direction and access controls.
This is an anonymized engagement summary published under EPC Group's anonymized-engagement rule: the client is not named, no commercial terms are published, and every statement is EPC-reported. Named, documented engagements are in the Evidence Center.
Problem and scope
| Item | Scope |
|---|---|
| Organization | A defense technology company |
| Situation | Two source GCC High tenants after an acquisition, to be consolidated into one destination GCC High tenant |
| Baseline | Up to 300 users |
| Production migration | Exchange Online, SharePoint Online, OneDrive for Business and in-scope Power Automate workflows. Teams chat, channel and file migration excluded |
| Phase 1 (weeks 1–2) | Readiness, inventory, identity validation and a representative pilot |
| Phase 2 (weeks 3–6) | Critical-user production waves |
| Phase 3 (weeks 7–9) | Remaining user waves |
| Phase 4 (weeks 10–11) | Close-out, compliance evidence, stabilization and formal hand-off |
| Workstreams | File services stage 1 for a DFS-replicated environment of a few terabytes (discovery, classification, Azure landing target, permissions, access validation, cut-over planning); permission, group and identity-mapping re-architecture (naming conventions, group taxonomy, UPN collisions); a hybrid identity exit roadmap; endpoint architecture, pilot and Intune/Defender validation with a transition runbook; mobile and BYOD app-protection discovery and pilot; Power Automate remediation for workflows that point to changing SharePoint URLs; migration-impact review of destination governance controls |
| Explicit follow-on work (excluded) | Full Purview classification, CUI tagging, DLP redesign and Copilot governance implementation; report redevelopment or Fabric work; full hands-on migration of every device |
| Governance | Lead-architect accountability for go/no-go and rollback decisions; named backup coverage; a licensing and entitlement readiness gate; acceptance and deemed-acceptance terms |
Not reported: mailbox and content volumes, wave dates and any measured result.
Approach and artifacts
Re-scope honestly after discovery. Version 3.0 sets out what changed after the final technical discovery session. Each item that was not in the original workload list is shown with its new treatment:
- file services
- permission re-architecture
- workflows that point to SharePoint URLs that will change
- endpoint and mobile transition
- downstream report dependencies
The client reviews the complete plan before signing.
Pilot, then waves, with a way back. A representative pilot comes before any production wave. Critical users move first, and rollback authority sits with the lead architect.
Draw the line around compliance work. The migration includes a migration-impact review and readiness validation of the destination's governance controls. Purview classification, CUI tagging, DLP redesign and Copilot governance are named as follow-on work, so the migration scope stays clear.
What EPC Group delivered and what is not claimed
| Claim | Basis | Status |
|---|---|---|
| The company contracted EPC Group to consolidate two GCC High tenants into one | EPC engagement record | Contracted (EPC-reported) |
| Waves completed, cut-over done, or measured results | Not reported | Not claimed |
Related services
Microsoft 365 consulting · CMMC and GCC High · All case studies · Talk to a senior architect
Last updated by Errin O'Connor, Founder & Chief AI Architect, EPC Group
Related service: M&A Microsoft 365 Tenant Migration Assessment
Author: Errin O'Connor, Founder & Chief AI Architect, EPC Group · Published October 25, 2026 · Project alias EPC-2026-ANON-DEF-GCCHT2T · Published under the anonymized-engagement rule.