# Prepare a file

POST /v1/sessions/{session_id}/files: Prepare file metadata before uploading bytes.

POST<code>/v1/sessions/&#123;session_id&#125;/files</code>

Prepare file metadata before uploading bytes. Check `session_files_supported` on the session first. The response carries an opaque `id` and a `content_url`; upload exactly `size_bytes` bytes there. File routes return `404` when attachments are disabled for the environment, and prepare and content transfer return `409` when this agent version lacks file support.

Generated from the Platform API specification on 2026-09-04.

## Path parameters

| Parameter | Type | Description |
|---|---|---|
| `session_id` | string | The session, as returned by Create a session. |

## Headers

| Header | Required | Description |
|---|---|---|
| `Authorization` | yes | `Bearer` plus a short-lived OAuth access token issued for the Tanomis API audience. Backends obtain tokens with an [organization automation client](/guides/run/authenticate-your-backend); the CLI's human login is not an application credential. |
| `X-Organization-ID` | yes | The `organization_id` from the workspace projection you selected in `GET /v1/me/workspaces`. |
| `X-Workspace-Tenant-ID` | yes | The nested `tenant_id` from the same projection. A header cannot widen what the token grants. Some single-workspace or self-hosted environments take `X-Tenant-ID` instead, as supplied by their administrator. |

## Request body

| Field | Type | Required | Description |
|---|---|---|---|
| `filename` | string | required |  |
| `media_type` | string | required |  |
| `size_bytes` | integer | required |  |
| `sha256` | string | required | Hex digest of the bytes you will upload. |
| `idempotency_key` | string | optional | Replays the same prepared file for the same request. |

## Responses

| Status | Meaning |
|---|---|
| `201` | The prepared file. |
| `404` | File attachments are disabled for the environment, or no such session. |
| `409` | The deployed agent version does not support files. |

## Request

```bash
curl -X POST "https://api.tanomis.com/v1/sessions/ses_7d4f9c/files" \
  -H "Authorization: Bearer $TANOMIS_TOKEN" \
  -H "X-Organization-ID: $TANOMIS_ORG" \
  -H "X-Workspace-Tenant-ID: $TANOMIS_WORKSPACE" \
  -H "Content-Type: application/json" \
  -d '{
    "filename": "case-summary.pdf",
    "media_type": "application/pdf",
    "size_bytes": 48213,
    "sha256": "83e0ef2f426dfad68f9b420304fc19414f8451a6bf24667f7e61c50e9ca57f14",
    "idempotency_key": "case-summary-v1"
  }'
```

```python
import httpx

response = httpx.post(
    f"https://api.tanomis.com/v1/sessions/{session_id}/files",
    headers={
        "Authorization": f"Bearer {token}",
        "X-Organization-ID": organization_id,
        "X-Workspace-Tenant-ID": tenant_id,
    },
    json={
        "filename": "case-summary.pdf",
        "media_type": "application/pdf",
        "size_bytes": 48213,
        "sha256": "83e0ef2f426dfad68f9b420304fc19414f8451a6bf24667f7e61c50e9ca57f14",
        "idempotency_key": "case-summary-v1",
    },
)
response.raise_for_status()
result = response.json()
```

```typescript
const response = await fetch(`https://api.tanomis.com/v1/sessions/${sessionId}/files`, {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${token}`,
    "X-Organization-ID": organizationId,
    "X-Workspace-Tenant-ID": tenantId,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "filename": "case-summary.pdf",
    "media_type": "application/pdf",
    "size_bytes": 48213,
    "sha256": "83e0ef2f426dfad68f9b420304fc19414f8451a6bf24667f7e61c50e9ca57f14",
    "idempotency_key": "case-summary-v1"
  }),
});
if (!response.ok) throw new Error(`${response.status} ${await response.text()}`);
const result = await response.json();
```

## Response

```json title="201 Created"
{
  "id": "file_b172c9",
  "filename": "case-summary.pdf",
  "media_type": "application/pdf",
  "size_bytes": 48213,
  "sha256": "83e0ef2f426dfad68f9b420304fc19414f8451a6bf24667f7e61c50e9ca57f14",
  "status": "prepared",
  "content_url": "https://api.tanomis.com/v1/sessions/ses_7d4f9c/files/file_b172c9/content",
  "created_at": "2026-09-02T11:45:00Z"
}
```