> ## 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.

# USDC system events

> Reference for how Arc emits USDC balance-change events: the native system Transfer log (EIP-7708) and the ERC-20 USDC contract events, with emitter addresses, signatures, and decimals for indexers.

For a step-by-step indexing walkthrough, see
[Index Arc events](/integrate/infrastructure/indexing-events). For the
conceptual model behind USDC's native and ERC-20 interfaces, see
[Stablecoin native model](/arc/concepts/stablecoin-native-model).

## Two event streams

USDC movements surface as logs from two distinct emitters. The native system
emitter logs a `Transfer` for **every** USDC movement—native sends and ERC-20
transfers alike—so it is a single universal record of balance changes at
18-decimal precision. Filter by emitter address to tell the two streams apart.

| Source                             | Emitter address                              | Events     | Decimals |
| :--------------------------------- | :------------------------------------------- | :--------- | :------- |
| **Native USDC** (system, EIP-7708) | `0xfffffffffffffffffffffffffffffffffffffffe` | `Transfer` | 18       |
| **ERC-20 USDC** (NativeFiatToken)  | `0x3600000000000000000000000000000000000000` | `Transfer` | 6        |

<Warning>
  A single ERC-20 `transfer()` emits **two** logs: the ERC-20 contract's own
  `Transfer` (6 decimals, from `0x3600000000000000000000000000000000000000`) and
  the native system `Transfer` (18 decimals, from
  `0xfffffffffffffffffffffffffffffffffffffffe`). A plain native send emits only
  the system log. Match on the emitter address so you do not count the same
  movement twice, and never mix the 6-decimal and 18-decimal values.
</Warning>

## Native USDC system events (EIP-7708)

Native USDC movements emit a standard ERC-20 `Transfer` log from a designated
system address. This is Arc's implementation of
[EIP-7708](https://eips.ethereum.org/EIPS/eip-7708), an Amsterdam-track Ethereum
proposal that Arc ships ahead of upstream. Native movements can be indexed the
same way as ERC-20 transfers. (For the legacy events that testnet emitted before
this behavior was activated, see
[Historical events](#historical-events-before-zero5).)

The log covers native value transfers (`CALL`), contract creation with an
endowment (`CREATE`), `SELFDESTRUCT` balance transfers, and the
precompile-driven `mint`, `burn`, and `transfer` operations that back the ERC-20
USDC interface.

| Property | Value                                                                |
| :------- | :------------------------------------------------------------------- |
| Emitter  | `0xfffffffffffffffffffffffffffffffffffffffe`                         |
| Event    | `Transfer(address indexed from, address indexed to, uint256 value)`  |
| topic0   | `0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef` |
| Decimals | 18                                                                   |

Mint and burn are expressed as transfers involving the zero address:

* **Mint:** `Transfer(0x0, recipient, amount)`
* **Burn:** `Transfer(from, 0x0, amount)`

The following rules apply to the system `Transfer` log:

* The native `Transfer` log is emitted **first**, before any other logs in the
  transaction.
* Zero-value transfers emit no log.
* Self-transfers (`from == to`) emit no log.
* A native value transfer (`CALL`, `CREATE`, or `SELFDESTRUCT`) to or from the
  zero address reverts with `"Zero address not allowed"`. Mint and burn are the
  only paths that produce a `Transfer` involving `0x0`, and they go through the
  precompile.

## ERC-20 USDC contract events

The NativeFiatToken contract at
[`0x3600000000000000000000000000000000000000`](/arc/references/contract-addresses#usdc)
emits its own standard ERC-20 `Transfer` log (**6 decimals**) for activity on
the ERC-20 interface. As on any ERC-20 token, mint and burn surface here as a
`Transfer` to and from the zero address. These events are independent of the
native system events: an ERC-20 `transfer()` produces a log from both emitters.

| Property | Value                                                                |
| :------- | :------------------------------------------------------------------- |
| Emitter  | `0x3600000000000000000000000000000000000000`                         |
| Event    | `Transfer(address indexed from, address indexed to, uint256 value)`  |
| topic0   | `0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef` |
| Decimals | 6                                                                    |

## Historical events (before Zero5)

On testnet, before the Zero5 hard fork activated, native USDC movements emitted
custom events from the NativeCoinAuthority precompile at
`0x1800000000000000000000000000000000000000` (18 decimals) instead of the
standard `Transfer` log. These events are **no longer emitted** after
activation. Mainnet has used the EIP-7708 `Transfer` log since genesis, so this
only affects indexers that backfill pre-activation testnet history.

| Event                                                                             | topic0                                                               |
| :-------------------------------------------------------------------------------- | :------------------------------------------------------------------- |
| `NativeCoinTransferred(address indexed from, address indexed to, uint256 amount)` | `0x62f084c00a442dcf51cdbb51beed2839bf42a268da8474b0e98f38edb7db5a22` |
| `NativeCoinMinted(address indexed recipient, uint256 amount)`                     | `0xb049859d09b3a7d0189a07db4d4becee1a2aa269023205478b1360ab6fc12114` |
| `NativeCoinBurned(address indexed from, uint256 amount)`                          | `0xaaf1ef013644e67c5cea90217acdf0accd334f8437fc9a89a53cfc9b25fb5c25` |

If you backfill history across the hard fork boundary, read `NativeCoin*` from
`0x1800000000000000000000000000000000000000` for blocks before activation and
`Transfer` from `0xfffffffffffffffffffffffffffffffffffffffe` at and after
activation. For the exact activation time and node version requirements, see the
canonical `arc-node`
[CHANGELOG.md](https://github.com/circlefin/arc-node/blob/main/CHANGELOG.md) and
[BREAKING\_CHANGES.md](https://github.com/circlefin/arc-node/blob/main/BREAKING_CHANGES.md#v071),
and the [Run an Arc node](/arc/tutorials/run-an-arc-node) tutorial.

## Out of scope: gas fees and block rewards

Gas fees and block rewards are **not** emitted as `Transfer` events and are
unaffected by EIP-7708:

* **Gas fees** are derived from the receipt (`gasUsed × effectiveGasPrice`).
* **Block rewards** are attributed via `block.miner`.

## See also

* [Index Arc events](/integrate/infrastructure/indexing-events)—step-by-step
  indexing walkthrough with code
* [Stablecoin native model](/arc/concepts/stablecoin-native-model)—why USDC has
  native and ERC-20 interfaces
* [Contract addresses](/arc/references/contract-addresses)—USDC and other system
  contract addresses
* [EVM compatibility for developers](/arc/references/evm-differences)—interface-level
  guidance and EVM differences