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

> ## Agent Instructions
> Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}.
> Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts.
> Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md.
> Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md.
> Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.
> Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.
> Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming.
> Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md.
> Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors.
> API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.
> Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes.
> When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records.
> Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md.

# Going to production

> Transition your Digital Asset Accounts integration from sandbox to production

## 1. Request production access

Contact your [Circle representative](mailto:sales@circle.com) to request
production API access. Production access requires a signed agreement with
Circle.

## 2. Replace sandbox URLs with production URLs

Update the base URL in your application from the sandbox endpoint to the
production endpoint.

| Environment | API host |
| :- | :- |
| Sandbox | `https://api-sandbox.circle.com` |
| Production | `https://api.circle.com` |

## 3. Replace your API key

Replace your sandbox API key with your production API key. Your production API
key is provided by Circle after your production access is approved.

<Warning>
  **Keep your production API key safe.** Because the production API key allows you
  to work with real funds, treat it with appropriate security protocols. Never
  expose it in client-side code or public repositories.
</Warning>

If you operate in an EU/EEA member state under MiCA, your entity also
authenticates to Circle with mutual TLS (mTLS). mTLS applies to all of your
entity's API traffic as the distributor, not per end user, and uses the regional
EU API endpoint. See
[How mTLS authentication works](/circle-mint/mtls-authentication).

## 4. Account for production settlement times

In sandbox, wire deposits and blockchain transactions settle instantly. In
production, be aware of the following differences:

| Operation | Sandbox behavior | Production behavior |
| - | - | - |
| Wire deposits | Instant | 1-2 business days |
| Wire withdrawals | Instant | 1-2 business days |
| Crypto deposits | Instant | Varies by blockchain (minutes to hours) |
| Crypto transfers | Instant | Varies by blockchain (minutes to hours) |
| Internal transfers | Instant | Instant (same as sandbox) |

Update your application's user interface to set the right expectations for your
end customers about processing times.

## 5. Verify KYB onboarding flow

In sandbox, KYB verification is automatically approved. In production, Circle
performs real KYB checks on your end customers. Ensure your integration handles
the following scenarios:

* **Pending verification**: The account is created but not yet active while
  Circle reviews the business entity
* **Rejected verification**: The business entity does not pass KYB checks and
  the account is not activated

## 6. Review transaction limits

Sandbox limits differ from production limits. Verify the applicable limits for
your end customers' risk tiers and ensure your integration handles limit errors
gracefully. See
[Limits and risk ratings](/digital-asset-accounts/concepts/limits-and-risk-ratings)
for details.

## 7. Set up webhook notifications

If you haven't already, configure
[webhook notifications](/api-reference/webhook-endpoints#v2-notifications) for
your production environment to receive real-time updates on deposits,
withdrawals, and transfers. Using webhooks reduces the need for polling and
ensures you respond quickly to account events.

## Production checklist

Before going live, confirm that you have completed each of the following items:

* Obtained a production API key from Circle
* Updated all API calls to use the production base URL
* Tested authentication with the production API key
* Handled KYB pending and rejected states in your onboarding flow
* Accounted for real-world settlement times in your user interface
* Configured webhook notifications for production
* Verified that transaction limit errors are handled gracefully