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URL: https://platform.claude.com/docs/en/managed-agents/files

⇱ Adding files - Claude API Docs

Attach and download files
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You can provide files to your agent by uploading them through the Files API and mounting them in the session's sandbox.

All Managed Agents API requests require the managed-agents-2026-04-01 beta header. The SDK sets the beta header automatically.

Uploading files

First, upload a file using the Files API:

file = client.beta.files.upload(file=Path("data.csv"))
print(f"File ID: {file.id}")

Mounting files in a session

Mount uploaded files into the sandbox by adding them to the resources array when creating a session:

The mount_path is optional, but make sure the uploaded file has a descriptive name so the agent can identify it.

A new file_id is created that references the instance of the file in the session. These copies do not count against your storage limits.

Multiple files

Mount multiple files by adding entries to the resources array:

A maximum of 100 files is supported per session.

Managing files on a running session

You can add or remove files from a session after creation using the session resources API. Each resource has an id returned when it is added (or listed), which you use for deletes.

List all resources on a session with resources.list. To remove a file, call resources.delete with the resource ID:

Listing and downloading session files

Use the Files API to list files scoped to a session and download them.

Supported file types

The agent can work with any file type, including:

  • Source code (.py, .js, .ts, .go, .rs, and others)
  • Data files (.csv, .json, .xml, .yaml)
  • Documents (.txt, .md)
  • Archives (.zip, .tar.gz) - the agent can extract these using bash
  • Binary files - the agent can process these with appropriate tools

File paths

Files mounted in the sandbox are read-only copies. The agent can read them but cannot modify the original uploaded file. To work with modified versions, the agent writes to new paths within the sandbox.

  • Files are mounted at the exact path you specify
  • Parent directories are created automatically
  • Paths should be absolute (starting with /)

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session = client.beta.sessions.create(
 agent=agent.id,
 environment_id=environment.id,
 resources=[
 {
 "type": "file",
 "file_id": file.id,
 "mount_path": "/workspace/data.csv",
 },
 ],
)
resources = [
 {"type": "file", "file_id": "file_abc123", "mount_path": "/workspace/data.csv"},
 {"type": "file", "file_id": "file_def456", "mount_path": "/workspace/config.json"},
 {"type": "file", "file_id": "file_ghi789", "mount_path": "/workspace/src/main.py"},
]
resource = client.beta.sessions.resources.add(
 session.id,
 type="file",
 file_id=file.id,
)
print(resource.id) # "sesrsc_01ABC..."
listed = client.beta.sessions.resources.list(session.id)
for entry in listed.data:
 print(entry.id, entry.type)

client.beta.sessions.resources.delete(resource.id, session_id=session.id)
# List files associated with a session
files = client.beta.files.list(
 scope_id="sesn_abc123",
 betas=["managed-agents-2026-04-01"],
)
for f in files:
 print(f.id, f.filename)

# Download a file
content = client.beta.files.download(files.data[0].id)
content.write_to_file("output.txt")