Beginner's question: How does file upload and context work exactly?

Hello everyone, I've noticed a few recurring questions from newcomers about the mechanics of file handling in Kimi. As someone who thinks a lot about data movement and context management, I wanted to map out a clear, step-by-step guide on how this feature actually works under the hood. It's a powerful tool, but understanding its boundaries helps plan its use effectively, much like planning a small data migration.

Let's break down the "file upload and context" process into a numbered path. Think of each upload as creating a temporary, isolated data repository for your conversation.

**Step 1: The Upload & Processing Phase**
When you upload a file (a PDF, Word doc, TXT, PPT, Excel, or image), Kimi doesn't just "look at it." It performs an extraction, reading and converting the text content into a format it can process. This is similar to an ETL (Extract, Transform, Load) job. For images, it uses OCR (Optical Character Recognition) to pull out the text. This phase happens immediately after upload, and there's a brief processing "downtime" of a few seconds, depending on file size and complexity.

**Step 2: Context Injection into the Active Session**
The extracted text is then injected into the *context window* of *that specific chat*. It does not go into Kimi's general knowledge base. This context window is a rolling conversation memory. The new text from your file is added to the top of this memory stack, alongside your recent questions and its answers.

**Step 3: Working Within Limits – The Critical Constraint**
Here’s the most important part: the context window has a finite size, measured in tokens (roughly, pieces of words). Kimi's context is large, but it's not infinite. The text from your uploaded file consumes a portion of this budget. Once the combined total of your file's text, your questions, and Kimi's responses approaches the limit, the system starts to "forget" the oldest information in the chat to make room for the new. This means:
* If your file is very large, only the initial portions may remain in active context as the conversation progresses.
* You cannot directly reference content from a file uploaded in *Chat A* while you are in *Chat B*. Each chat session is a separate, ephemeral container.

**Step 4: Practical Implications for Your Workflow**
* **For long documents:** Consider breaking them into logical chunks (e.g., by chapter) and uploading them one at a time into a single chat when you are ready to discuss that specific section. This gives you the most relevant context for each deep-dive.
* **For data analysis:** Uploading an Excel sheet allows Kimi to reason about the structure and numbers it sees. However, for complex analysis across multiple sheets, you may need to guide it step-by-step, as the context limit may prevent it from holding the entire dataset in memory at once.
* **Persistence:** The file itself is not stored permanently on Kimi's servers for you to access later. The *conversation* is saved, but if you start a new chat tomorrow, you will need to re-upload the file to establish that context again.

In essence, file upload creates a powerful, yet temporary and sandboxed, knowledge pool for a single conversation thread. It's perfect for focused analysis sessions, much like spinning up a dedicated database for a particular reporting job. I hope this step-by-step explanation helps you plan your interactions more effectively! What specific file types or use cases are you all trying to tackle?