GCC Eligibility and Configuration

Does my organization need GCC High if we handle CUI but are not directly subject to ITAR?

Handling CUI does not automatically require GCC High if the data is not subject to ITAR, EAR, or DFARS 252.204-7012 clauses. The specific regulatory obligation tied to the CUI determines which Microsoft cloud environment is appropriate, not the CUI designation alone.

If your contract includes DFARS 7012 clauses, Microsoft recommends GCC High for CMMC 2.0 Level 2 compliance, even without ITAR applicability. DFARS 7012 requires the use of a cloud service provider with FedRAMP authorization, and GCC High's FedRAMP High certification is the most direct path to meeting that requirement within Microsoft's ecosystem. For CUI that falls under CMMC Level 1 only (handling Federal Contract Information without higher sensitivity requirements), standard GCC or even a properly configured commercial environment may be sufficient. The safest approach is to review the specific CUI category markings on your contract and consult with your contracting officer. If any CUI in your environment is subject to DFARS 7012, ITAR, or requires FedRAMP High cloud hosting, GCC High is the appropriate environment.

Can a subcontractor use GCC High Teams calling to receive calls from a prime contractor on a standard commercial tenant?

GCC High and commercial Microsoft 365 tenants are isolated environments, so standard Teams-to-Teams calling between them does not work natively. A subcontractor on GCC High cannot receive a direct Teams Phone call from a prime contractor on a commercial tenant as if they were on the same platform.

Cross-cloud communication is possible through specific configurations. Microsoft Entra business-to-business (B2B) collaboration can be set up to allow limited cross-cloud guest access, and Teams Cross-Cloud Guest Access enables commercial tenant users to join GCC High Teams meetings with some limitations. However, for regular PSTN voice calls (standard phone calls using phone numbers), the call simply routes through the public telephone network regardless of which Microsoft cloud environment either party uses. The subcontractor's GCC High Teams Phone number rings like any other phone number when dialed from any phone, including a commercial Teams tenant. The compliance boundary is maintained because the subcontractor's call data, metadata, and logs stay within the GCC High environment. The limitation applies specifically to Teams-native calling features and collaboration, not to traditional phone calls between numbers.

Does GCC High Teams calling work if some of our employees are still on a commercial Microsoft 365 license?

GCC High Teams calling works for users licensed in the GCC High tenant, but it does not extend to employees on a commercial Microsoft 365 license. The two tenants operate as separate, isolated environments with no native interoperability for Teams calling or file sharing.

Many organizations use an "enclave" approach where only employees who process, store, or access CUI are licensed in GCC High, while the rest of the workforce stays on commercial Microsoft 365. This reduces licensing costs because GCC High licenses are priced higher than commercial equivalents. The trade-off is operational complexity: users in the commercial tenant cannot directly call GCC High users through Teams-native calling. They can reach each other through standard PSTN phone numbers (dialing the actual phone number), and cross-cloud B2B guest access can be configured through Microsoft Entra for limited meeting and collaboration scenarios. Organizations running a split-tenant model need clear data governance policies that define which employees handle CUI, which workflows stay within GCC High, and how cross-tenant communication is managed without creating compliance gaps.