Microsoft 365 Copilot Semantic Index helps Copilot find relevant information in Microsoft Graph data using both keyword matching and meaning. It does not give users new access to company files: Copilot grounds answers in content each user is already authorised to view. For organisations, the practical priorities are accurate permissions, suitable content, and deliberate search governance—not a global switch to turn the index off.
What Semantic Index is
Microsoft describes Semantic Index as an advanced lexical and semantic index generated from Microsoft Graph data. The lexical layer helps find matches to words; the semantic layer helps identify material relevant to a concept or intent even when a question does not use the exact terms in a document. Together with Graph’s content relationships and permission context, it helps Copilot retrieve useful material from Microsoft 365.
This is retrieval and grounding, not training Copilot on an organisation’s files. Microsoft says prompts, responses, and data accessed through Microsoft Copilot are not used to train foundation large language models. Microsoft’s documentation also says requests use HTTPS encryption and customer data remains encrypted at rest.
How Copilot uses the index to answer a question
- A user submits a prompt in a Microsoft 365 app.
- Copilot accesses Microsoft Graph and Semantic Index to find relevant context.
- Copilot sends a modified prompt to the language model and receives a response.
- Copilot accesses Graph and Semantic Index again to post-process the response before returning an answer or taking an app action.
The index informs search and retrieval; it is not a separate chatbot or a guarantee that every relevant file will be found. Content must be supported, searchable, available to the user, and indexed for it to contribute.
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What content is indexed, and how quickly
Microsoft’s supported-content documentation lists user mailbox data and the following file or page types for user- and tenant-level scenarios where applicable:
- Word: DOC and DOCX
- PowerPoint: PPTX
- ASPX web pages
Microsoft states that files up to 512 MB are supported for PDF, PPTX, and DOCX extensions. That figure applies to those listed extensions; it should not be treated as a size allowance for every format.
For tenant-level SharePoint indexing, Microsoft says new documents on accessible SharePoint Online sites are indexed daily when the sites are accessible through inheritance by two or more users. Changes to documents that are already indexed are indexed immediately. This does not mean every newly uploaded SharePoint file is instantly searchable: permissions, site search settings, content type, and indexing eligibility still matter.
What Copilot can see: permissions and privacy
Permission trimming is the core access boundary. Microsoft says Copilot presents organisational data only when the individual user has at least view permission, and Semantic Index honours the user identity-based access boundary. It does not grant new rights or make a private document visible to someone who could not already access it under Microsoft 365 controls.
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That safeguard does not correct overly broad permissions. If a SharePoint site or file has been shared too widely, Copilot may retrieve it for users who already have access. Before deployment, review group membership, inherited permissions, external sharing, sensitivity labels, and applicable Microsoft Purview controls. These are governance measures for the underlying content and access model, not a substitute for permission trimming.
Can administrators turn Semantic Index off or exclude a site?
Microsoft describes semantic indexing as automatically enabled and as an improvement to Microsoft 365 Search; administrators cannot disable it globally. They can govern what is discoverable by managing permissions, applying Purview controls, and excluding a SharePoint Online site from search.
To exclude a site, set Allow this site to appear in search results to No. Microsoft says this excludes the site from both Microsoft Search and the tenant-level semantic index; there is no separate control to exclude it from only one of those systems. Consider this for especially sensitive payroll, HR, or financial sites where reduced discoverability is appropriate. Exclusion reduces search discovery, but it does not replace a permissions review.
How external company data reaches Copilot
Native Microsoft 365 content and external-system content follow different routes:
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| Approach | Where content comes from | Access and administration | Important boundary |
|---|---|---|---|
| Native Semantic Index | Microsoft Graph data, including supported Microsoft 365 content | Uses Microsoft 365 permissions; core semantic indexing is automatic, with SharePoint search exclusions and governance controls available to administrators | Searchability depends on supported content, indexing, and the user’s existing access |
| Copilot connectors | External services such as knowledge bases, ticketing systems, wikis, file stores, and CRM tools | An administrator decides which connectors are enabled; access to connector content depends on permissions in the underlying source | Ingestion and synchronization add a dependency and freshness can vary by connector |
| Copilot Search API | OneDrive for work or school | Requires the Microsoft 365 Copilot license add-on and supports path-based filtering while preserving existing security and compliance controls | The preview API does not currently support SharePoint or Copilot Connectors as data sources |
Using Copilot connectors
Microsoft Support describes connectors as a way to make content from services outside Microsoft 365 available in Copilot and Microsoft 365 search experiences. Copilot can summarise and cite connector content, but connector enablement is an administrator decision and the user must be permitted to access the information in the underlying system.
If expected material is missing, check that the connector is enabled, confirm the user has direct access in the source system, make the query specific, and account for the connector’s indexing or synchronization timing. A connector does not erase the source system’s permission model or guarantee that changes appear immediately.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What developers should know about the Copilot Search API
The Microsoft 365 Copilot Search API is a preview API for hybrid semantic and lexical search across OneDrive for work or school. Microsoft says it can interpret natural-language intent, return relevant files and metadata, filter by path, and leave data in place while respecting existing security and compliance controls. The supported source scope is narrower than Microsoft 365 Copilot itself: SharePoint and Copilot Connectors are not supported data sources in the API at this time.
Microsoft Learn’s API documentation, updated October 20, 2025, lists these limits:
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- Full keyboard experience. Features a full mechanical keyset, backlit keys, and a large trackpad for precise navigation and control. Optimal key spacing allows fast, fluid typing.
- Slim and compact Performs like a traditional, full-size keyboard.
- Clicks in place instantly Use in combination with the Surface Pro (11th Edition), Pro 9 and Pro 8* kickstand for a perfect laptop experience anywhere.
- Query parameter: up to 1,500 characters.
- Maximum page size: 100 results.
- Rate limit: up to 200 requests per user per hour.
The API documentation lists semantic-search support for these extensions: ASPX, DOCX, PPTX, PDF, ONEPART, DOC, HTML, EML, MP4, LOOP, ONE, FLUID, PNG, JPG, JSON, CSV, XML, and PPT. This API-specific list is broader than the file types listed in Microsoft’s general Semantic Index supported-content table; it should not be read as proof that every extension is supported in every Copilot search experience. Microsoft also says semantic search does not support nontextual content such as tables, images, and charts, and files above its documented size thresholds are unsupported.
Because the API is in beta, Microsoft warns that it may change and is not suitable for production applications unless the developer accepts that preview risk. Its current source scope, licensing requirement, and limits should be checked against the API documentation before designing an integration.
Licensing and availability
In a January 15, 2024 announcement, Microsoft said it removed the 300-seat minimum for Copilot for Microsoft 365, made the product broadly available to businesses, and extended Semantic Index to Office 365 users with a paid Copilot license. That announcement provides historical availability context, not a complete statement of every current plan’s eligibility.
For the Copilot Search API specifically, Microsoft Learn says it is available at no extra cost to users who have a Microsoft 365 Copilot license add-on; support for users without that add-on is not currently available. Do not assume that general Copilot availability and API access have identical licensing requirements.
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