Microsoft Copilot Notebook Source Limit: Maximum Files and Token Budget

When you use Copilot Notebook in Microsoft 365, you can attach multiple files to ground the AI response in your specific data. However, there are hard limits on how many files you can attach and how much text the system can process at once. Exceeding these limits causes Copilot to truncate the input, ignore additional files, or return incomplete answers. This article explains the exact maximum file count and token budget for Copilot Notebook, how the system allocates tokens across files, and what happens when you hit these limits.

Copilot Notebook Source Limits: File Count and Token Budget

Copilot Notebook is a feature within Microsoft 365 Copilot that lets you upload local files, SharePoint documents, or OneDrive files to serve as context for a single conversation. The feature is designed for deep analysis of multiple documents, such as comparing contract clauses across several PDFs or synthesizing data from quarterly reports. To maintain performance and cost predictability, Microsoft enforces two primary limits: a maximum file count and a token budget.

Maximum File Count

You can attach up to 20 files to one Copilot Notebook session. This limit applies regardless of the file type. If you try to attach a 21st file, Copilot displays an error message stating that the maximum number of sources has been reached. The count includes files uploaded directly from your device, files linked from SharePoint, and files selected from OneDrive. Each file counts as one source, even if the file is empty or contains only a few bytes.

Token Budget

The token budget for a single Copilot Notebook session is 128,000 tokens. Tokens are units of text that the AI model processes. A token is roughly four characters or 0.75 words in English. The budget includes the text content of all attached files plus your prompt. Copilot truncates the combined input to fit within 128,000 tokens. If your files contain more text than the budget allows, Copilot processes only the first 128,000 tokens and ignores the rest. This truncation can lead to missing data in the AI response.

File Size Limit

Individual files must be 512 MB or smaller. Files larger than 512 MB are rejected immediately, and Copilot does not attempt to tokenize them. This limit applies to all file types, including PDF, DOCX, XLSX, TXT, and image files. Note that image files are not converted to text for token processing. Only the text extracted from images using OCR counts toward the token budget, and the image itself is not analyzed.

How Token Allocation Works Across Attached Files

When you attach multiple files, Copilot concatenates the text from each file in the order they appear in the attachment list. The system then applies the 128,000-token limit to this concatenated text plus your prompt. Files attached earlier in the list get priority. If the total exceeds the budget, Copilot truncates the later files first. For example, if you attach three files with a combined text of 150,000 tokens, Copilot keeps the first 128,000 tokens and discards the remaining 22,000 tokens from the third file.

The prompt you type also consumes tokens. A long prompt reduces the budget available for file content. A short prompt leaves more tokens for the attached files. To maximize the amount of file content that Copilot processes, keep your prompt under 500 tokens. This gives the full 127,500 tokens to the attached files.

Configuring Copilot Notebook Limits in Microsoft 365 Admin Center

Administrators cannot change the file count or token budget limits. These limits are hard-coded by Microsoft. However, administrators can control which users have access to Copilot Notebook through licensing. Only users with a Copilot for Microsoft 365 license can use the Notebook feature. To verify or assign licenses, follow these steps.

1. Open the Microsoft 365 admin center
   Go to admin.microsoft.com and sign in with a Global Admin or Billing Admin account.
2. Navigate to Billing > Licenses
   In the left navigation pane, select Billing, then select Licenses.
3. Select the Copilot for Microsoft 365 license
   Find the product named Copilot for Microsoft 365 and click on it.
4. Assign licenses to users
   Select the users who should have access to Copilot Notebook, then click Assign. Users must also have a Microsoft 365 E3 or E5 license.

Common Issues When Hitting Source Limits

Copilot Ignores Files Beyond the 20th

If you attach more than 20 files, Copilot displays a warning and does not include the extra files. To work around this limit, split your analysis into multiple Notebook sessions. For example, analyze the first 20 files in one session, then start a new session for the next set of files.

Copilot Returns Incomplete Answers Due to Token Truncation

When the combined token count exceeds 128,000, Copilot silently truncates the input. The AI response may reference data that was cut off, leading to missing or incorrect conclusions. To avoid this, check the total token count of your files before attaching them. Use a tokenizer tool or estimate by multiplying the word count by 1.33. If the total exceeds 128,000 tokens, remove the least important files or shorten the files themselves.

Large Files Cause Slow Performance

Files close to the 512 MB limit take longer to upload and tokenize. Copilot may appear unresponsive for several seconds while processing a large file. To improve performance, split a large file into smaller chapters or sections before attaching it to Notebook.

Copilot Notebook Limits vs Copilot Chat Limits: Comparison

Item	Copilot Notebook	Copilot Chat
Maximum files per session	20	3
Token budget	128,000 tokens	16,000 tokens
Individual file size limit	512 MB	10 MB
File types supported	PDF, DOCX, XLSX, TXT, image files for OCR	PDF, DOCX, XLSX, TXT, image files for OCR
Prompt length impact	Reduces file token budget	Reduces file token budget
Administrator override	Not available	Not available

Copilot Notebook offers significantly higher file and token limits compared to standard Copilot Chat. This makes Notebook the better choice for analyzing large document sets. Use Copilot Chat for quick queries with one or two small files.

You can now identify the maximum file count and token budget for Copilot Notebook. To avoid truncation, keep your total input under 128,000 tokens and attach no more than 20 files. For deep multi-document analysis, split your work into separate Notebook sessions. As an advanced tip, pre-process your files by removing redundant sections or compressing images to reduce the token count before attaching them to Notebook.