> For the complete documentation index, see [llms.txt](https://docs.shredpay.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.shredpay.xyz/developers/agent-wallet/concepts/gas-model.md).

# Gas Model

Two ways to pay for gas. Knowing which applies to which call is the difference between "this transaction worked" and "out of funds."

| Mode                  | Who pays                                                  | When it applies                                                                                                  | Service fee                                         |
| --------------------- | --------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------- | --------------------------------------------------- |
| **Agent pays**        | The sub-wallet's own native balance (ETH, BNB, MATIC, …). | `send_transaction` and any direct call you make through `POST /api/tx/send`.                                     | None.                                               |
| **ShredPay sponsors** | ShredPay's gas wallet on the target chain.                | `execute_swap`, `defi_deposit`, `defi_withdraw`, `gas_swap` — all flows that go through the **Router** contract. | A small fee on the input amount, in the same token. |

## Why two modes

Agents need to be able to call arbitrary contracts (paying their own gas keeps the model simple and uncensorable). But the most common operations — swaps, deposits, withdrawals — go through ShredPay's Router contract, which can batch token approvals and the actual call into a single sponsored transaction. That's faster, cheaper, and avoids the "agent has USDC but no ETH for gas" footgun.

## When you must hold native gas

Any time you call `send_transaction`. Typical examples:

* ERC-20 transfers to addresses outside the Router.
* Direct calls to a third-party protocol that ShredPay does not have a Router pathway for.
* Any custom calldata.

If your sub-wallet runs out of native gas mid-flow, use [`gas_swap`](/developers/agent-wallet/guides/gas-management.md) — it converts USDC to ETH through the Router with **ShredPay** paying gas, so the agent doesn't need ETH to obtain ETH. This is how an agent funded only in USDC bootstraps itself.

> **Today `gas_swap` is supported on Base only.** Plan accordingly if your agent operates on other chains — pre-fund native gas or hold the agent on Base.

## When ShredPay sponsors

Any time you call:

* `execute_swap` — swap one token for another.
* `defi_deposit` / `defi_withdraw` — vault interactions in the curated DeFi catalog.
* `gas_swap` — bootstrap native gas from USDC.

These calls only succeed on chains where the **Router** contract is deployed. Check `has_router` in `GET /api/wallet/chains`:

```json
{
  "chains": [
    { "id": 1,     "name": "Ethereum", "has_router": false },
    { "id": 8453,  "name": "Base",     "has_router": true  },
    { "id": 42161, "name": "Arbitrum", "has_router": false }
  ]
}
```

A sponsored call on a chain without Router returns `400 ROUTER_NOT_AVAILABLE`.

## Service fees

Sponsored flows charge a small fee (basis points on the input amount, taken in the same token). Fees are returned in every quote — they are never a surprise:

```json
{
  "amount_in": "100000000",
  "amount_out": "0.0473...",
  "fee_amount": "100000",
  "fee_token": "USDC",
  "gas_sponsored": true
}
```

For exact current fee schedules, check the response body of `POST /api/swap/quote` — they are sourced live, not from documentation.

## Gas estimation

```http
GET /api/gas/estimate?chain_id=8453
```

```json
{
  "chain_id": 8453,
  "gas_price_wei": "1000000",
  "recommended_eth_for_5_txs": "0.0005",
  "native_balance_wei": "120000000000000"
}
```

Use this to decide whether the wallet has enough headroom for the next few transactions, or whether to swap up first.

## Related

* [Manage Gas guide](/developers/agent-wallet/guides/gas-management.md) — how to keep the wallet topped up
* [Multi-chain](/developers/agent-wallet/concepts/multi-chain.md) — which chains have Router