Microsoft Copilot Context Window Explained: token limits, memory behavior

The context window of Microsoft Copilot determines how much text, how many pages, and how many documents the system can process during a single request or workflow. In late 2025, Copilot uses a combination of token-based limits for its underlying language models and document-based limits in Microsoft 365 apps, where Word, Excel, PowerPoint, Outlook, and Teams rely on retrieval pipelines that break files into chunks before feeding them to the model. This creates a layered system where theoretical capacity, practical behavior, and policy rules differ depending on the surface. Copilot’s context system is shaped by model architecture, Microsoft Graph integration, and enterprise governance settings that define what Copilot can remember, retain, or use across sessions.

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Copilot applies surface-specific context rules: token windows for model-level chat and page/word limits for Microsoft 365 documents.

In Copilot Chat, GitHub Copilot, and Studio-based environments, the system uses model-level token windows that fall around 64 000 to 128 000 tokens for newer builds. These are the sessions where the model’s raw context window is most visible. In Microsoft 365 applications, Copilot uses a different method: instead of loading entire documents into the token window, it retrieves relevant sections using the Microsoft Graph, breaks files into segments, and passes only selected parts into the model. This allows Copilot to handle extremely large documents—hundreds of pages—without exceeding token limits, though the system will only reference sections considered relevant.

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Surface-Based Context Behavior — Copilot (late 2025)

Surface	Effective Context Handling	Underlying Mechanism	Typical Workload
Copilot Chat	64k–128k token windows	Direct prompt loading	Research, Q&A
GitHub Copilot	64k+ tokens depending on model	Code-based context	Multi-file coding
Word/Excel/PowerPoint	Page and section retrieval	Microsoft Graph chunking	Long documents
Outlook	Thread and attachment retrieval	Email/thread detection	Email drafting
Teams	Meeting notes and chat history	Conversation segmentation	Collaboration tasks

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Copilot can process extremely long documents through retrieval mechanisms, even when the model’s token window is smaller than the full document size.

Microsoft documentation and partner reports indicate that Copilot can summarize documents up to approximately 1.5 million words (~300 pages) in Word or PowerPoint by segmenting files and retrieving relevant chunks. The system does not load full documents into context; instead, it uses retrieval augmentation to extract only the needed portions. This creates a hybrid system where the theoretical context window is maintained, but the effective usable context is extended using indexing.

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Document-Length Capacity — Copilot (Microsoft 365)

Document Type	Approx. Maximum Length	Context Handling	Behavior
Word (.docx)	~300 pages	Retrieval-based	Full-document summaries
PowerPoint	Large decks with many slides	Slide chunking	Topic summaries
Excel	Multiple sheets (limited depth)	Table extraction	Cell/column-focused
PDF imports	Hundreds of pages	OCR + segmentation	Extractive summaries

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Rewriting, editing, and long-form generation operate under smaller practical limits compared to summarization and analysis.

Although Copilot can summarize hundreds of pages, rewriting tasks require smaller sections to maintain coherence. Microsoft guidance indicates that for rewriting, restructuring, or multi-step editing, users should operate within ~3 000 words, allowing the system to preserve logical consistency. This practical limit reflects how the context window is consumed during generation, as rewriting tasks require simultaneous access to larger parts of the input than summarization tasks do.

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Practical Limits for Writing and Rewriting

Task Type	Recommended Input Size	Reason	Effect
Summarization	Very large (hundreds of pages)	Retrieval-based	Accurate top-level synthesis
Rewriting	~3 000 words	Requires deeper context	Higher coherence
Paragraph editing	Short sections	Local context	Good for detailed revisions
Multi-document Q&A	Multiple files	Cross-retrieval	Relies on Graph

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File size limits differ across Copilot surfaces, with enterprise tiers supporting up to 512 MB per file.

Microsoft’s file-handling rules vary depending on licensing and environment. Enterprise Microsoft 365 Copilot allows users to upload files up to 512 MB each, supporting workflows with large PDFs, heavy PowerPoint decks, and multi-sheet spreadsheets. Standard consumer or lightweight Copilot versions—such as Copilot Chat for personal accounts—have more restrictive file sizes, historically ranging from 1 MB to 10 MB but currently scaling upward depending on feature rollout.

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File Size Constraints — Copilot (late 2025)

Tier or Environment	File Size Limit	Typical Behavior	Use Case
Microsoft 365 Enterprise	Up to 512 MB	Handles large documents	Corporate workflows
Standard Microsoft 365	Moderate limits	Reliable across Word/Excel	Mid-size files
Copilot Chat (free)	Lower limits	Restrictive for PDFs	Personal tasks
Developer tools	Varies by platform	Optimized for code contexts	Multi-file coding

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Memory behavior depends on licensing: enterprise memory is persistent, while consumer and lightweight tiers have reduced or no memory features.

Microsoft’s “Copilot Memory” is not uniform across surfaces. In enterprise settings, memory can store user preferences, recurring tasks, or contextual patterns, though administrators may enable or disable the feature. For personal accounts or consumer-facing versions of Copilot Chat, memory functionality may be disabled or limited. Memory does not store full conversations; instead, it registers user intentions, formatting preferences, and frequently used prompts to guide future responses. Policy settings determine how long memory persists and what the model may recall.

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Memory Behavior Across Copilot Surfaces

Environment	Memory Features	Retention	Notes
Microsoft 365 Enterprise	Full memory	Persistent	Admin-controlled
Microsoft 365 Personal	Partial/limited	Varies	Not all apps supported
Copilot Chat (free)	No memory	None	Stateless
GitHub Copilot	Code-context memory	Session-based	Does not store personal data

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Policy rules introduced in 2025 govern tool-use limits, image generation caps, and retrieval behavior across Microsoft 365 applications.

By 2025, Microsoft introduced stricter caps for image generation and tool usage in Copilot Chat when accessed without a full Microsoft 365 Copilot license. Similar restrictions apply to file analysis: although large files may be readable, only a portion of their content will enter the model’s effective context during any single request. Administrators in enterprise settings can disable memory, restrict attachment processing, or modify what Copilot may access through Graph permissions. This establishes a governance layer that controls data exposure and ensures compliance across organizations.

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2025 Policy Rules — Microsoft Copilot

Policy Area	Behavior	Impact	Notes
Image generation	Daily caps in light tiers	Restricted creativity tools	Full access with Microsoft 365
File analysis	Retrieval-limited	Only relevant chunks loaded	Helps with large docs
Admin controls	Enable/disable memory	Enterprise governance	24h propagation
Attachment access	Permission-based	Limits email/file usage	Graph-driven constraints

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Copilot’s context window in late 2025 combines direct token limits, retrieval augmentation, and enterprise governance to create a flexible but tier-dependent system.

Users working with long documents or multi-file workflows benefit from retrieval-based context expansion, while coding and chat surfaces depend more on strict token windows. Enterprise customers access larger files, broader memory features, and more consistent cross-application context. Across all surfaces, Copilot’s context system reflects a structure optimized around Microsoft Graph and governed by licensing and administrative rules.

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