GCC vs GCC High: Key Differences

Many government organizations underestimate the differences between Microsoft GCC and GCC High. When choosing a government cloud environment, they often select based on what seems faster, simpler, cheaper, or easier to access. However, making the wrong decision can create significant compliance challenges that become difficult, expensive, and disruptive to change later.

Microsoft offers multiple government cloud environments because government data isn’t all regulated in the same way. While GCC and GCC High share many surface-level similarities, they serve very different risk profiles and regulatory obligations. These differences may seem minor at first, but they become critical as workloads expand to include controlled data, defense-related programs, or regulated communications like voice.

In this guide, we will uncover the key differences between GCC and GCC High, from eligibility and compliance to security architecture, Teams, and calling. This information will help government agencies and contractors choose the right environment with confidence and avoid costly missteps down the line.

What Are GCC and GCC High?

To understand the differences, let’s start by defining each cloud environment and what it was built for.

What Is Microsoft GCC?

Microsoft’s Government Community Cloud (GCC) serves federal civilian agencies, state and local governments, and contractors that do not handle defense-regulated data. It provides a secure, U.S.-based cloud aligned with FedRAMP Moderate or High, depending on context, and supports most non-defense government workloads.

What Is Microsoft GCC High?

GCC High specifically caters to defense contractors, DoD agencies, and organizations that handle controlled unclassified information or export-controlled data. It operates on Azure Government with strict physical and logical isolation, offering alignment with FedRAMP High, ITAR, DFARS, and CMMC. Its purpose is to ensure data sovereignty, controlled access by U.S. citizens, and compliance for defense-related workloads.

Eligibility and Intended Use Differences

The most important distinction between GCC and GCC High lies in who is eligible to use each environment and the types of workloads they support. These environments are not interchangeable, and eligibility closely relates to the regulatory obligations associated with an organization’s contracts and data.

GCC Eligibility

Microsoft GCC is designed for U.S. government agencies and contractors whose work does not involve defense-regulated or export-controlled data.

GCC is typically appropriate for:

• State, local, tribal, and civilian federal agencies
• Government contractors that do not handle DoD-controlled unclassified information (CUI)
• Organizations whose compliance requirements stop short of ITAR-, DFARS-, or CMMC-driven obligations
  
  

GCC provides a government-aligned cloud environment that supports common compliance requirements without the added isolation and restrictions required for national security or defense workloads.

GCC High Eligibility

GCC High is reserved for organizations that support defense, national security, or export-controlled programs and must meet stricter federal compliance requirements.

GCC High is typically required for:

• Defense contractors and organizations within the Defense Industrial Base (DIB)
• Agencies and programs that handle DoD CUI
• Environments subject to ITAR, DFARS, or CMMC requirements
  
  

GCC High is built to support these regulated workloads, meaning access is restricted, and eligibility must be validated. Organizations must demonstrate a legitimate government or defense relationship (e.g., an active contract, CAGE code, or government sponsorship) before Microsoft provisions a GCC High tenant.

This validation process ensures that only organizations with a clear regulatory need can operate in GCC High, keeping data, users, and services within the compliance boundaries required for defense and national security environments.

Compliance and Regulatory Differences

Compliance requirements represent one of the clearest dividing lines between GCC and GCC High. Both cloud services are designed to support very different regulatory scopes, especially when dealing with defense or export-controlled data.

GCC Compliance Scope

GCC aligns with government compliance requirements and suits many civilian agency and contractor workloads. Its compliance posture typically aligns with FedRAMP Moderate, although FedRAMP High-level controls may apply depending on the service and deployment context.

However, GCC does not support export-controlled or defense-regulated data. It lacks the level of isolation, access restrictions, or contractual assurances required for ITAR, DFARS, or CMMC-governed environments. For organizations handling DoD-controlled data or national security programs, this limitation becomes a critical constraint rather than a technical nuance.

GCC High Compliance Scope

GCC High is built specifically to meet FedRAMP High requirements and to support workloads subject to ITAR, DFARS, and CMMC obligations. It applies a higher baseline of security controls, including NIST 800-53 high-impact controls, and operates within an environment designed to meet defense and export-control expectations.

This is also why Microsoft limits ITAR-aligned contract language and support to GCC High. Meeting ITAR and related regulations requires guarantees around data residency, access by U.S.-citizen personnel, and operational isolation that GCC is not designed to provide. Rather than extending those assurances across all government clouds, Microsoft confines them to GCC High, where they can be consistently enforced.

Security Architecture and Data Sovereignty Differences

GCC and GCC High enforce security and data sovereignty through different architectural models, and those differences become increasingly important as workloads move beyond basic collaboration and into regulated communications.

GCC Security Model

GCC provides U.S.-based data residency and operates within Microsoft’s government cloud framework. Data is logically separated from the commercial Microsoft cloud, and access controls are aligned with standard government security requirements.

This model is sufficient for many civilian government workloads and non-defense use cases. However, GCC relies primarily on logical separation, meaning it does not provide the same level of physical isolation or operational restrictions required for defense-regulated or export-controlled environments.

GCC High Security Model

GCC High runs entirely within Azure Government, which is both physically and logically isolated from Microsoft’s commercial cloud infrastructure. This isolation is a core requirement for supporting national security and defense workloads.

Access to customer data in GCC High is restricted to U.S.-citizen Microsoft personnel who undergo enhanced screening. Services are operated under stricter controls designed to meet federal and DoD requirements. These measures apply not only to stored data, but also to operational elements such as call signaling, voicemail, and administrative access.

GCC High’s security architecture provides data sovereignty and access assurances for organizations handling defense-related collaboration or regulated voice communications that GCC is not intended to offer.

Teams Phone and PSTN Calling Differences

Microsoft Teams is available in both GCC and GCC High, but PSTN calling works differently in each environment. These differences often reveal that an organization's initial cloud choice may no longer be sufficient.

Teams Phone in GCC

In GCC, Teams Phone can be deployed using multiple supported calling models, depending on the organization’s needs and compliance boundaries. This flexibility makes GCC suitable for many civilian government agencies and contractors whose voice communications are not tied to defense-regulated or export-controlled workloads.

GCC voice is sufficient when:

• PSTN calling supports administrative or non-defense use cases
• Voice traffic does not involve DoD CUI or ITAR-regulated programs
• Compliance requirements align with GCC’s baseline controls
  
  

For these scenarios, Teams Phone in GCC can function much like a government-aligned version of commercial Teams calling, without the added architectural constraints imposed by national security requirements.

Teams Phone in GCC High

Microsoft Calling Plans and Operator Connect aren’t available in GCC High. So any organization looking to enable PSTN calling must do so via Direct Routing.

This means organizations must use a GCC High–compliant carrier and architecture that aligns with Azure Government, U.S.-only data residency, and U.S.-citizen access controls. Call signaling, media, voicemail, emergency services, and administrative access are all subject to the same regulatory expectations as other defense-related workloads.

Adding PSTN calling is often what pushes organizations from GCC into GCC High because PSTN calling expands the scope of regulated data. Call metadata, recordings, and operational access can fall under ITAR, DFARS, or CMMC obligations in ways that chat or meetings alone may not. 

Cost and Operational Complexity Differences

The most visible differences between GCC and GCC High are the differences in cost and operational complexity. The two environments carry very different overhead depending on the level of compliance and assurance required.

GCC Cost and Complexity

GCC generally has a lower barrier to entry than GCC High. Eligibility requirements are broader, onboarding is more straightforward, and fewer validation steps are required before workloads can be deployed.

Operationally, GCC environments are easier to manage because they support a wider range of standard Microsoft 365 services and calling models. For organizations with clearly defined, non-defense workloads, this means lower upfront costs, faster deployment timelines, and less ongoing administrative overhead.

GCC High Cost and Complexity

GCC High’s compliance posture means that it comes with additional cost and operational requirements. Eligibility must be validated, infrastructure runs within Azure Government, and access controls are more restrictive. To use Teams Phone, you’ll need Direct Routing and compliant voice providers.

These additional requirements mean longer planning cycles, more coordination across IT, compliance, and telecom teams, and higher ongoing operational costs compared to GCC. It’s important to keep in mind that this complexity reflects the controls needed to support defense-regulated and export-controlled workloads.

In the long run, any organization that requires GCC High but chooses a lower-cost environment like GCC will pay for it further down the line due to compliance gaps, audit findings, or disruptive migrations. These outcomes are typically far more expensive than deploying the correct environment from the start.

How to Decide: GCC or GCC High?

If you’re still unsure which environment you need, the decision usually comes down to a few practical and compliance-driven factors. The points below can help you quickly determine which cloud aligns with your organization’s obligations.

Choose GCC if:

• Your organization does not handle DoD-controlled unclassified information (CUI) or ITAR-regulated data
• Your contracts and compliance requirements are clearly defined and stop short of defense or export-control obligations
• Teams Phone is limited to administrative or non-defense use cases

Choose GCC High if:

• You are part of the Defense Industrial Base (DIB) or support DoD programs
• Your contracts reference ITAR, DFARS, or CMMC requirements
• Teams Phone and PSTN calling support or touch-regulated workflows
• You want to avoid the risk of migrating environments later as compliance needs expand
  
  

The most important thing about this decision is that it’s best make it before deployment, when architectural changes are still straightforward, and compliance boundaries are easier to enforce.

How Atlantech Helps Organizations Navigate GCC vs GCC High

Choosing between GCC and GCC High often requires understanding their different eligibility rules, compliance obligations, and voice architecture to know whether an environment is viable long term. Atlantech works with government agencies and contractors to help align cloud, voice, and compliance requirements before deployment decisions are locked in.

Atlantech guides eligibility and compliance alignment, and helps organizations validate whether GCC is sufficient or whether GCC High is required based on contract language, data types, and regulatory scope. We help reduce the risk of selecting an environment that later proves noncompliant once workloads expand.

For organizations operating in or moving to GCC High, Atlantech delivers GCC High–compliant Teams Phone and PSTN calling using Direct Routing, which is the only supported calling model in that environment. The solution is designed specifically for Azure Government and supports compliance-driven requirements such as U.S.-only infrastructure and regulated data handling.

Atlantech also brings hands-on expertise with Direct Routing architecture and government voice deployments, helping organizations design, deploy, and operate Teams Phone in a way that aligns with GCC and GCC High constraints.

Choose the Environment That Matches Your Risk

When choosing a government cloud environment, your priority should be risk tolerance and regulatory obligation. GCC and GCC High exist to support different compliance thresholds, and Teams Phone often exposes those differences faster than collaboration workloads alone.

Choosing the correct environment upfront helps avoid compliance gaps, audit issues, and disruptive migrations later. The more regulated your data, contracts, and communications become, the more important it is that your cloud architecture reflects those realities from day one.

If you want help validating whether GCC or GCC High is the right environment for your organization’s compliance, security, and Teams calling requirements, request a consultation with one of our government cloud and voice experts before you commit at scale.