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

# App Kit SDK: Unified Balance

> Create a chain-agnostic USDC balance and spend it instantly on any blockchain with the App Kit SDK's Unified Balance capability.

The [App Kit SDK](/app-kit) includes the Unified Balance capability that
combines USDC from multiple blockchains into a single, instantly spendable
balance. It is built on top of
[Circle Gateway](https://developers.circle.com/gateway) and handles the Gateway
workflow for deposits and spends across EVM and non-EVM blockchains.

## How it works

Unified Balance works by depositing funds held across multiple blockchains into
a single, chain-agnostic Unified Balance. Those funds are then available to
spend instantly on any blockchain.

The process is illustrated below:

```mermaid theme={null}
flowchart LR
  A[Chain A wallet] -->|"deposits funds"| UB[(Unified Balance)]
  B[Chain B wallet] -->|"deposits funds"| UB
  C[Chain C wallet] -->|"deposits funds"| UB
  UB -->|"spends funds"| D[Chain D wallet]
```

### What to know about wallet models

* Some wallet models cannot sign their own Unified Balance spends, including
  Circle Wallets SCAs and Privy server wallets. Use the
  [delegate workflow](/app-kit/quickstarts/unified-balance-delegate-deposit-and-spend):
  the wallet remains the depositor, and an authorized EOA signs each spend.

* Circle Wallets are chain-specific. For Unified Balance flows that draw from
  multiple source blockchains, use the wallet address for each source
  blockchain.

* For Unified Balance spends, create one source per wallet and chain as needed.
  The Circle Wallets adapter is stateless, so you can reuse the same adapter
  configuration and pass the wallet address in each operation context.

* Circle Wallets smart contract account (SCA) deposits require
  `allowanceStrategy: "approve"`. USDC permit signatures use `ecrecover`, which
  does not accept the SCA's ERC-1271 signature, so the SDK uses an onchain
  `approve`.

<Info>
  Unified Balance is built on Circle Gateway. For production considerations
  related to deposits, spends, and fund removal, see the
  [Gateway implementation checklist](https://developers.circle.com/gateway/references/technical-guide#implementation-considerations).
</Info>

## Quick look

This code snippet creates a Unified Balance by depositing funds from two
blockchains to spend on a third:

```typescript TypeScript theme={null}
// Deposit 1.00 USDC into the Unified Balance from Base
const depositBase = await kit.unifiedBalance.deposit({
  from: { adapter: viemAdapter, chain: "Base_Sepolia" },
  amount: "1.00",
  token: "USDC",
});
// Deposit 1.00 USDC into the Unified Balance from Arbitrum
const depositArb = await kit.unifiedBalance.deposit({
  from: { adapter: viemAdapter, chain: "Arbitrum_Sepolia" },
  amount: "1.00",
  token: "USDC",
});
// Spend 1.50 USDC from the Unified Balance on Arc
const spendResult = await kit.unifiedBalance.spend({
  amount: "1.50",
  from: { adapter: viemAdapter },
  to: {
    adapter: viemAdapter,
    chain: "Arc_Testnet",
    recipientAddress: "0xRecipientAddress",
  },
});
```

For a complete end-to-end flow, follow the quickstart for your scenario:

* [Deposit and spend a Unified Balance](/app-kit/quickstarts/unified-balance-deposit-and-spend)
* [Use a delegate to deposit and spend a Unified Balance](/app-kit/quickstarts/unified-balance-delegate-deposit-and-spend)

## Installation

[Install the App Kit SDK](/app-kit/tutorials/installation) to use Unified
Balance. If you only need Unified Balance and don't want to install the full App
Kit SDK, follow the steps below to install the standalone Unified Balance Kit.

<Steps>
  <Step title="Install Unified Balance Kit">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/unified-balance-kit
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/unified-balance-kit
      ```
    </CodeGroup>
  </Step>

  <Step title="Install adapters">
    Use the [adapter setup guide](/app-kit/tutorials/adapter-setups) to choose the
    right wallet model for your app, including browser wallets and Circle Wallets.

    <Tabs>
      <Tab title="Viem">
        <CodeGroup>
          ```bash npm theme={null}
          npm install @circle-fin/adapter-viem-v2 viem
          ```

          ```bash yarn theme={null}
          yarn add @circle-fin/adapter-viem-v2 viem
          ```
        </CodeGroup>
      </Tab>

      <Tab title="Ethers">
        <CodeGroup>
          ```bash npm theme={null}
          npm install @circle-fin/adapter-ethers-v6 ethers
          ```

          ```bash yarn theme={null}
          yarn add @circle-fin/adapter-ethers-v6 ethers
          ```
        </CodeGroup>
      </Tab>

      <Tab title="Solana">
        <CodeGroup>
          ```bash npm theme={null}
          npm install @circle-fin/adapter-solana-kit @solana/kit @solana/web3.js
          ```

          ```bash yarn theme={null}
          yarn add @circle-fin/adapter-solana-kit @solana/kit @solana/web3.js
          ```
        </CodeGroup>
      </Tab>

      <Tab title="Circle Wallets">
        <CodeGroup>
          ```bash npm theme={null}
          npm install @circle-fin/adapter-circle-wallets
          ```

          ```bash yarn theme={null}
          yarn add @circle-fin/adapter-circle-wallets
          ```
        </CodeGroup>
      </Tab>
    </Tabs>
  </Step>
</Steps>