---
title: CreateMultipartUpload · S3 API
description: Starts a multipart upload and returns its upload ID.
doc_version: 0.1.0-preview
last_updated: 2026-09-14
---

# CreateMultipartUpload

`POST /{bucket}/{key}?uploads`

Starts a multipart upload and returns its upload ID.

A multipart upload writes a large object in parts. Start it here, send each part with UploadPart, then join the parts with CompleteMultipartUpload.

- Role: Editor or higher.
- Support: supported.
- Auth: AWS Signature Version 4 with your API key. See [S3 API](/api/s3.md).
- Starts an upload. aws s3 cp uses multipart for large files.
- Storage keeps only Content-Type from this request. The object gets no metadata, tags, or other stored headers.

## Example request

```http
POST /support-tickets/big.bin?uploads HTTP/1.1
Host: wspq7ws2np5l8z4.storage.beta.graphon.sh
x-amz-date: 20261007T093000Z
x-amz-content-sha256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
Authorization: AWS4-HMAC-SHA256 Credential=<ACCESS_KEY_ID>/20261007/us-east-1/s3/aws4_request, SignedHeaders=host;x-amz-content-sha256;x-amz-date, Signature=<SIGNATURE>
```

## Path parameters

- `bucket` (string, required): The bucket name.
- `key` (string, required): The object key. Keep each `/` as it is. Percent-encode the other reserved characters.

## Query parameters

- `uploads` (flag, required): Selects this operation. Send it with no value.

## Headers

- `Content-Type` (string, optional): The media type of the object. Default: `application/octet-stream`.
- `x-amz-expected-bucket-owner` (string, optional): The workspace ID that must own the bucket. Another owner returns `403 AccessDenied`.

## Responses

### 200 · OK

The upload started.

Response body:

- `InitiateMultipartUploadResult` (object, required): The root element.
  - `Bucket` (string, optional): The bucket name.
  - `Key` (string, optional): The object key.
  - `UploadId` (string, optional): The ID that the other multipart calls take.

```http
HTTP/1.1 200 OK
Content-Type: application/xml
x-amz-request-id: 4F8A2C7D1E6B4093A5C2D8E1F7B3A960

<?xml version="1.0" encoding="UTF-8"?>
<InitiateMultipartUploadResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
  <Bucket>support-tickets</Bucket>
  <Key>big.bin</Key>
  <UploadId>VXBsb2FkIGZvciBiaWcuYmlu</UploadId>
</InitiateMultipartUploadResult>
```

## Errors

Any request can also get the common errors on [S3 API](/api/s3.md).

### 404 · `NoSuchBucket`

No bucket has this name, or the bucket was deleted.

Check the bucket name. ListBuckets shows the buckets of the workspace.

### 403 · `AccessDenied`

The key does not have the role for this operation, or the bucket is in another workspace.

Use a key of the workspace that owns the bucket, with the role above.

## Other request languages

### aws CLI

```bash
# The graphon profile from the S3 API overview.
export AWS_PROFILE=graphon

aws s3api create-multipart-upload --bucket support-tickets --key big.bin
```

### Python (boto3)

```python
# Replace wspq7ws2np5l8z4 with your workspace ID.
import os

import boto3
from botocore.config import Config

api_key = os.environ["GRAPHON_API_KEY"]
access_key_id = api_key.split("_", 1)[1].split(".")[0]

s3 = boto3.client(
    "s3",
    endpoint_url="https://wspq7ws2np5l8z4.storage.beta.graphon.sh",
    region_name="us-east-1",
    aws_access_key_id=access_key_id,
    aws_secret_access_key=api_key,
    config=Config(signature_version="s3v4", s3={"addressing_style": "path"}),
)

response = s3.create_multipart_upload(
    Bucket="support-tickets",
    Key="big.bin",
)
print(response["UploadId"])
```

### JavaScript (AWS SDK)

```javascript
// Replace wspq7ws2np5l8z4 with your workspace ID.
import { S3Client, CreateMultipartUploadCommand } from '@aws-sdk/client-s3';

const apiKey = process.env.GRAPHON_API_KEY;
if (!apiKey) throw new Error('Set GRAPHON_API_KEY.');
const accessKeyId = apiKey.split('_')[1].split('.')[0];

const s3 = new S3Client({
  endpoint: 'https://wspq7ws2np5l8z4.storage.beta.graphon.sh',
  region: 'us-east-1',
  forcePathStyle: true,
  credentials: { accessKeyId, secretAccessKey: apiKey },
});

const response = await s3.send(new CreateMultipartUploadCommand({
  Bucket: 'support-tickets',
  Key: 'big.bin',
}));
console.log(response.UploadId);
```

## Sitemap

See the full [sitemap](/sitemap.md) for all pages.