When you ask Copilot a question, it sometimes generates an answer even when it lacks supporting data from your documents or the web. This behavior, known as speculation, produces responses that are not grounded in verified information. The root cause is Copilot’s default fallback to its language model when it cannot find relevant sources. This article explains how to configure Copilot to stop speculating and only answer when it can cite a source.
You will learn the specific settings in Microsoft 365 and Windows that control grounded responses. The instructions cover Copilot in Microsoft 365 apps, the Copilot side pane in Windows, and the web interface at copilot.microsoft.com. By the end, you can enforce a strict source-only policy for every Copilot interaction.
Key Takeaways: Configuring Copilot to Require Sources
- Microsoft 365 admin center > Copilot > Data sources: Restricts Copilot to only use Microsoft Graph data and disables fallback to the base model.
- Copilot pane > Settings > Plugins: Disabling web search plugins prevents Copilot from pulling unverified online data.
- Copilot in Windows 11 > Group Policy > Turn off grounded responses without sources: Forces Copilot to refuse answers when no document, email, or web source is available.
Why Copilot Speculates Without Sources
Copilot is built on a large language model that can generate text from patterns in its training data. When you ask a question, Copilot first searches for relevant sources in your Microsoft Graph data, SharePoint sites, OneDrive files, and web content if plugins are enabled. If it finds no matching source, it falls back to generating a response from its language model alone. This fallback is what causes speculation.
The fallback behavior is intentional. Microsoft designed Copilot to always try to answer rather than remain silent. For business users who need fact-based answers, this default is problematic. Speculation can produce plausible but incorrect information, leading to decisions based on false premises. The fix involves changing configuration settings that tell Copilot to stop when no source is found.
How the Fallback Works in Detail
When Copilot receives a query, it executes a search across connected data sources. The search returns snippets and documents ranked by relevance. If the relevance score of the top result falls below a threshold, the system treats the search as unsuccessful. At that point, Copilot switches to generative mode, using only the language model to compose an answer. This mode is not grounded in any source you can verify.
The threshold for treating a search as successful is not adjustable through user-facing settings. However, you can disable the fallback entirely through policy controls. The sections below explain how.
Steps to Stop Copilot From Speculating in Microsoft 365
The most effective method is to configure Copilot in the Microsoft 365 admin center. This setting applies to Copilot in Word, Excel, PowerPoint, Outlook, Teams, and the web interface.
- Open the Microsoft 365 admin center
Go to admin.microsoft.com and sign in with a Global Admin or Copilot Admin role. - Navigate to Copilot settings
Select Settings in the left navigation, then Org settings. Find Copilot in the list and click it. - Restrict data sources
Under Data sources, check the box Only use Microsoft Graph data. This tells Copilot to use only your organization’s data from SharePoint, OneDrive, and Exchange. Uncheck Allow Copilot to use web data if it is selected. - Disable the fallback model
Scroll to Generative fallback. Set the toggle to Off. This is the critical step. When off, Copilot will not generate a response if it cannot find a source in the selected data sources. - Save and test
Click Save. Open a document in Word and ask a question that has no matching content in your tenant. Copilot should respond with a message like “I couldn’t find relevant information in your organization’s data.”
Steps to Stop Copilot From Speculating in Windows 11
If you use Copilot in Windows 11, you can enforce the same behavior through Group Policy or the registry. This method applies to the Copilot side pane launched from the taskbar.
- Open Group Policy Editor
Press Win + R, type gpedit.msc, and press Enter. This tool is available in Windows 11 Pro, Enterprise, and Education editions. - Find the Copilot policy
Navigate to Computer Configuration > Administrative Templates > Windows Components > Copilot. - Enable the grounded responses policy
Double-click Turn off grounded responses without sources. Select Enabled. This policy tells Copilot to refuse to answer any query for which it cannot find a source in the configured data sources. - Apply the policy
Click OK. Run gpupdate /force in a Command Prompt window to apply the change immediately. - Test in Copilot
Press Win + C to open Copilot. Ask a question unrelated to your files, such as “What is the capital of a country I never mentioned?” Copilot should reply that it cannot find a source.
If Copilot Still Speculates After Configuration
Sometimes the settings do not take effect immediately or are overridden by other configurations. The following issues are the most common.
Copilot in Microsoft 365 still speculates
The generative fallback toggle in the admin center may not apply to all Copilot surfaces. Check whether the setting propagated to all users. It can take up to 24 hours for changes to replicate. Also verify that no conflicting policy exists in the Microsoft 365 apps admin center under Customization > Copilot settings. If a policy there allows web search, it can override the admin center setting.
Copilot in Windows 11 ignores the Group Policy
Group Policy settings require the Copilot app to be version 1.2.0 or later. Check your Copilot version by opening Copilot, clicking the three-dot menu, and selecting About. If the version is older, update Windows 11 to the latest release. Also confirm that the policy is not disabled by a higher-priority policy from your organization’s domain.
Copilot web interface at copilot.microsoft.com still speculates
The web version of Copilot does not use the same data source settings as the Microsoft 365 apps. To stop speculation on the web, you must use the Work tab and sign in with your work account. Then click the settings gear icon and select Data sources. Choose Only my organization’s data. This prevents the web interface from falling back to the public web or the base model.
Copilot Settings Comparison: Source-Only vs Default
| Item | Source-Only Configuration | Default Configuration |
|---|---|---|
| Data sources used | Microsoft Graph data only (SharePoint, OneDrive, Exchange) | Microsoft Graph data plus web data and base model |
| Generative fallback | Disabled | Enabled |
| Response when no source found | Refuses to answer with a source-not-found message | Generates a speculative answer from the language model |
| Administration method | Microsoft 365 admin center or Group Policy | No change needed |
| Best for | Business users who need fact-based answers only | General users who prefer an answer even if unverified |
You can now configure Copilot to refuse to speculate when no source is available. Start by applying the data source restriction in the Microsoft 365 admin center, then enforce the Group Policy on Windows 11 devices. For a comprehensive approach, also set the web interface to use only organizational data. As an advanced step, create a PowerShell script that applies the Group Policy to all domain-joined machines using the Set-ItemProperty cmdlet on the registry path HKLM\Software\Policies\Microsoft\Windows\Copilot.