Files API
The Files API is a storage service built into the Anthropic API that lets you upload files once and reuse them across multiple API requests. Instead of sending the same PDF, image, or dataset as raw bytes every time you make a request, you upload it once and get back a unique file_id. You then pass that file_id in your Messages API calls wherever you would have included the file content directly.
The API supports a standard set of file management operations: upload (POST /v1/files), list (GET /v1/files), retrieve metadata (GET /v1/files/{file_id}), delete (DELETE /v1/files/{file_id}), and download for files generated by the code execution tool (GET /v1/files/{file_id}/content). Files you upload cannot be downloaded back; only files produced by Claude's code execution tool can be retrieved.
The Files API is currently in beta. It is designed around a create-once, use-many-times pattern that reduces bandwidth, latency, and token-transmission overhead for workflows that repeatedly reference the same documents, images, or datasets. File content used in Messages requests is billed as standard input tokens.
When you’d use it
- ◆Document summarization pipeline — A legal team uploads contracts and regulatory filings once. Multiple analysts submit different summarization or Q&A requests against the same file_id without re-uploading the PDF each time, saving bandwidth and reducing request latency.
- ◆Iterative data analysis — A data analyst uploads a 200 MB CSV of sales transactions. They run several analytical queries in sequence—regional breakdowns, trend detection, anomaly checks—all referencing the same file_id, avoiding repeated large uploads.
- ◆Code execution data pipeline — A developer uploads a raw dataset, instructs Claude to write and execute Python code that cleans and aggregates the data, then downloads the generated output file using the Files API download endpoint, completing a full ETL loop inside the API.
- ◆Multi-turn visual troubleshooting — An engineer uploads a system architecture diagram once at the start of a debugging session. Every follow-up question in the conversation references the same file_id, so the image is never retransmitted even across dozens of turns.
- ◆Dynamic enterprise knowledge pool — An enterprise application pre-uploads 50 corporate policy documents. When an employee submits a question, routing logic selects the 3 most relevant documents by file_id and includes only those in the Messages request, giving Claude high-context answers without rebuilding a full vector database.
What changed recently
- ◆2025-04-14 — Files API launched in beta with the required header anthropic-beta: files-api-2025-04-14. Supports upload, list, retrieve metadata, delete, and download (for code-execution-generated files). Available on direct Anthropic API only at launch.
- ◆2026-04-01 — Files API became available on Claude Platform on AWS (Anthropic-managed infrastructure accessible through AWS with AWS billing and IAM authentication).
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