> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ostium.com/llms.txt
> Use this file to discover all available pages before exploring further.

# POST /v1/pimlico/sponsor

> Default Pimlico-compatible sponsorship endpoints used by SDK gasless modes.

Gasless SDK modes use a Pimlico-compatible bundler/paymaster endpoint by default.

Mainnet:

```text theme={null}
https://builder.prod.bedrock.ostium.io/v1/pimlico/sponsor?chainId=42161
```

Testnet:

```text theme={null}
https://builder.prod.bedrock.ostium.io/v1/pimlico/sponsor?chainId=421614
```

## SDK usage

The default is applied when you create a gasless client without a custom `pimlicoUrl`.

```ts theme={null}
const client = await OstiumClient.createDelegatedAndGasless({
  delegatePrivateKey: process.env.DELEGATE_PRIVATE_KEY as `0x${string}`,
  traderAddress: '0xTraderAddress',
});
```

Override it when you want to use a different ERC-4337 bundler/paymaster endpoint.

```ts theme={null}
const client = await OstiumClient.createSelfAndGasless({
  traderPrivateKey: process.env.TRADER_PRIVATE_KEY as `0x${string}`,
  pimlicoUrl: 'https://your-bundler.example.com',
});
```

This endpoint is used internally by the SDK submitter for gasless UserOperations. Non-gasless modes do not call it.