> ## Documentation Index
> Fetch the complete documentation index at: https://docs.privy.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Overview
> Sponsor transaction fees across all wallets using the Privy gas sponsorship engine.
Sponsor transaction fees across all wallets using the Privy gas sponsorship engine. Powered by [Alchemy](https://www.alchemy.com/docs/wallets).
Privy's **gas sponsorship** engine gives you flexible control over how transaction fees are paid across your wallets. Privy supports two modes:
* **App pays** — your app's gas credits cover fees for all users. Users transact without ever needing to hold ETH or native tokens.
* **User pays** — gas fees are covered using the wallet's USDC or USDT balance, with no ETH required. Your app's gas credits are not charged.
Ready to get started? See the [setup guide](/wallets/gas-and-asset-management/gas/setup).
## Supported networks
App pays sponsorship is available on all of the networks below.
**Mainnets:**
* Ethereum
* Base
* Optimism
* Polygon
* Arbitrum
* BNB Smart Chain
* Unichain
* Gnosis
* Plasma
* Berachain
* Warden
* Flow
* Fluent
* Edge
* Monad
* World Chain
* Story
* Ronin
* MegaETH
* Ink
* Shape
**Testnets:**
* Sepolia
* Base Sepolia
* OP Sepolia
* Polygon Amoy
* Arbitrum Sepolia
* Unichain Sepolia
* MegaETH Testnet
* Ronin Saigon
* Monad Testnet
* Ink Sepolia
* Fluent Testnet
* Edge Testnet
* Robinhood Testnet
* Shape Sepolia
**Mainnets:**
* Tempo
**Testnets:**
* Tempo Testnet
**Mainnets:**
* Solana
**Testnets:**
* Solana Devnet
Want support for more networks? [Reach out to us!](mailto:sales@privy.io)
User pays (token gas) is supported on the following EVM chains only. Solana is not supported.
| Chain | USDC | USDT | EURC | USDG | USDC.e |
| :------------------------- | :--: | :--: | :--: | :--: | :----: |
| Ethereum | ✓ | ✓ | ✓ | ✓ | — |
| Base | ✓ | ✓ | ✓ | — | — |
| Tempo | — | — | — | — | ✓ |
| Optimism | ✓ | ✓ | — | — | — |
| Arbitrum | ✓ | ✓ | — | — | — |
| Polygon | ✓ | ✓ | — | — | ✓ |
| Sepolia (testnet) | ✓ | ✓ | ✓ | ✓ | — |
| Base Sepolia (testnet) | ✓ | ✓ | ✓ | — | — |
| OP Sepolia (testnet) | ✓ | — | — | — | — |
| Arbitrum Sepolia (testnet) | ✓ | — | — | — | — |
| Polygon Amoy (testnet) | ✓ | — | — | — | — |
Tempo also accepts PathUSD and USDT0. On Tempo, user pays mode is supported through the [transfer
API](/wallets/actions/transfer/overview) only.
## How it works
### Ethereum and EVM chains
Privy leverages [EIP-7702](https://eip7702.io/) with **paymasters** to sponsor gas fees:
* User wallets are upgraded to smart contracts
* Paymasters cover gas costs automatically
* Users can transact immediately without holding ETH or native tokens
**Native gas sponsorship vs smart wallets**
Our [smart contract wallets](/wallets/using-wallets/evm-smart-wallets/overview) offering
creates a separate 4337-compatible contract account, where the embedded wallet is the signer.
Native gas sponsorship lets you:
* Sponsor gas for embedded wallets without creating a separate contract account
* Get set up without managing extra bundler or paymaster providers
* Use a simpler developer experience — just pass `sponsor: true`
*If you already have users with funds in smart contract wallets, we recommend continuing to
use smart contract wallets.*
### Tempo networks
For Tempo transactions (type 118), Privy uses Tempo's native fee-payer signature flow:
* Privy adds `fee_payer_signature` to the Tempo transaction before broadcast when `sponsor: true`
* This flow is native to Tempo and does not use ERC-4337 user operations, EIP-7702 wallet upgrades, or EVM paymasters, reducing overhead for faster transactions
Learn more about Tempo's native fee sponsorship in the [Tempo transaction
specification](https://docs.tempo.xyz/protocol/transactions/spec-tempo-transaction#fee-payer-signature-details).
### Solana and SVM chains
Privy uses a **fee payer wallet** to cover transaction costs:
* A Privy-managed fee payer wallet funded with SOL covers fees
* The fee payer updates the transaction's `feePayer` field and latest blockhash
* Users transact without needing to hold SOL
### Calculating gas fees
Privy automatically handles gas fee calculation and optimization. Gas sponsorship includes the
actual network gas cost plus a convenience fee for the managed service.
Looking for more granular control over gas pricing? Consider exploring [custom
setup](/wallets/gas-and-asset-management/gas/ethereum) options.
When a user initiates a transaction, Privy:
1. **Gets a gas quote** from the Alchemy ERC-20 paymaster to estimate the maximum fee
2. **Checks the wallet balance** — verifies the wallet holds enough to cover both the transaction amount and the estimated gas fee
3. **Submits the transaction** — a paymaster approval is bundled atomically with the call or calls, as an ERC-4337 user operation
4. **Paymaster collects the fee** — after execution, the paymaster collects the exact gas fee from the wallet's configured token balance
Through the [transfer API](/wallets/actions/transfer/overview), the gas token is always the token
being transferred. For example, when a user sends USDC on Base, the gas fee is also deducted in
USDC — no ETH is required. Through the
[`eth_sendTransaction`](/api-reference/wallets/ethereum/eth-send-transaction) and
[`wallet_sendCalls`](/api-reference/wallets/ethereum/wallet-send-calls) RPC methods, the gas token
is named explicitly with `sponsor_options`.