> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hubra.app/llms.txt
> Use this file to discover all available pages before exploring further.
# USDC Earn
> Stablecoin yield from the Hubra validator operator. Voltr-routed, audited venues, instant withdraws.
USDC Earn is Hubra's stablecoin route. You deposit USDC; the vault routes it across audited Solana lending venues for blended yield. You can withdraw any amount at any time, no cooldown, no fee.
This page is the **feature reference**: how the vault is wired, what the on-chain accounts look like, and what the deposit / withdraw transactions actually do.
***
## Architecture
```
┌──────────────────────────────┐
│ Hubra Earn (UI / API) │
└──────────────┬───────────────┘
│
Builds unsigned tx via
│
▼
┌──────────────────────────────┐
│ Voltr API (api.voltr.xyz) │
│ /vault/{vault}/deposit │
│ /vault/{vault}/direct- │
│ withdraw │
└──────────────┬───────────────┘
│
On-chain call
│
▼
┌──────────────────────────────┐
│ Voltr Vault Program │
│ 3maCu...6gNQ (vault PDA) │
└──────────────┬───────────────┘
│
Whitelisted adapters route to
│
┌──────────────────┼──────────────────┐
▼ ▼ ▼
Kamino Jupiter (other)
lending lending whitelisted
```
Hubra never holds USDC. The vault is a Solana program account governed by audited contracts; deposits and withdraws happen by the user's wallet calling the vault program directly.
***
## Vault metadata
The full machine-readable metadata for the Hubra Earn USDC vault:
```json theme={null}
{
"name": "Hubra Earn USDC",
"vaultAddress": "3maCuTJVPteZ2dFA8dADxz2EbpJHfoAG5txYhXDs6gNQ",
"underlyingName": "USD coin",
"assetSymbol": "USDC",
"assetMint": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
"assetTokenProgram": "TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA",
"assetIcon": "/images/tokens/usdc.png",
"receiptSymbol": "raUSDC",
"receiptMint": "53fZaJGDMHcfku8pzZak5obVFUUjVxwqRTF63M3SQiSS",
"icon": "https://7tjb2jhu6znbujvdbauzmsyhqtp42yedjgncsnsdphwtje7ukszq.arweave.net/_NIdJPT2WhomowgplksHhN_NYINJmik2Q3ntNJP0VLM",
"decimals": 9
}
```
| Field | Value | Notes |
| ------------------- | ------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `name` | Hubra Earn USDC | Display name. |
| `vaultAddress` | `3maCu...6gNQ` | The Voltr vault PDA. The on-chain account that holds USDC and routes it to whitelisted adapters. |
| `underlyingName` | USD coin | Long-form asset name. |
| `assetSymbol` | USDC | The asset deposited and ultimately withdrawn. |
| `assetMint` | `EPjFW...Dt1v` | Circle's USDC SPL mint on Solana mainnet. |
| `assetTokenProgram` | `Tokenk...5DA` | Standard SPL Token program. The vault uses the classic SPL Token interface, not Token-2022. |
| `assetIcon` | `/images/tokens/usdc.png` | Icon for the underlying asset. |
| `receiptSymbol` | raUSDC | Symbol of the share token minted on deposit. |
| `receiptMint` | `53fZa...QiSS` | The raUSDC SPL mint. Owned by the vault program. |
| `icon` | Arweave URL | Icon for the receipt token. Hosted on Arweave for permanence. |
| `decimals` | 9 | **raUSDC decimals.** Voltr vaults mint shares at 9 decimals regardless of the underlying asset's decimals (USDC is 6). The vault handles the unit conversion internally. |
USDC has 6 decimals on-chain (`1.50 USDC = 1_500_000` base units). raUSDC has 9 decimals. When reading raUSDC balances directly from the chain, scale by `10^9`, not `10^6`. The Hubra app and API surface USDC-denominated values to hide this asymmetry.
All four addresses are verifiable on Solscan.
The vault is built on the **Voltr** vault program. The receipt token (raUSDC) is minted by the vault when you deposit, and burned by the vault when you withdraw. Hubra does not control the mint; the vault program does.
***
## Deposit flow (technical)
### What happens
1. Hubra's API calls `POST https://api.voltr.xyz/vault/3maCu...6gNQ/deposit`.
2. Voltr returns an unsigned base64 transaction. Hubra normalizes it to standard base64 and forwards.
3. The transaction includes:
* SPL Token transfer instruction: USDC from your associated token account to the vault.
* Voltr vault deposit instruction: mints raUSDC at the current share price.
* (If needed) Associated token account creation for raUSDC.
4. Your wallet signs.
5. The transaction is broadcast. On confirmation, USDC is in the vault, raUSDC is in your wallet.
### Request shape (Voltr API, called server-side)
```json theme={null}
{
"userPubkey": "",
"lamportAmount": "",
"assetMint": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
"assetTokenProgram": "TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA"
}
```
`lamportAmount` is the USDC amount in base units. With USDC decimals = 6, `1.50 USDC = 1_500_000` base units. Hubra's API takes a decimal string from the caller and converts to base units server-side.
### Share-price math
raUSDC is minted at the current share price:
```
raUSDC_minted = USDC_deposited / share_price
```
Share price climbs over time as the vault's underlying allocations earn yield. Read it via Voltr's `/vault/{vault}/share-price` endpoint, surfaced through Hubra's [`GET /api/v1/strategies/usdc-earn`](/developer/endpoints/get-strategy).
### Programmatic deposit
```bash theme={null}
curl -X POST https://hubra.app/api/v1/stake \
-H 'Content-Type: application/json' \
-d '{
"strategy": "usdc-earn",
"wallet": "",
"amount": "100"
}'
```
Response:
```json theme={null}
{
"strategy": "usdc-earn",
"transaction": "",
"hubra_token": "",
"route": "voltr",
"signers": [""]
}
```
Sign the transaction locally and broadcast via [`POST /api/v1/broadcast`](/developer/endpoints/broadcast) with `route: "rpc"`. There is no Sanctum involvement; plain RPC handles the broadcast.
***
## Withdraw flow (technical)
USDC Earn supports **direct withdraw** only. Other Voltr vaults can have queued withdraws with a `withdrawalWaitingPeriod`; this one does not.
### Direct withdraw
`POST https://api.voltr.xyz/vault/3maCu...6gNQ/direct-withdraw` returns an unsigned transaction that:
1. Burns your raUSDC.
2. Transfers USDC from the vault to your associated USDC token account.
3. Settles in a single transaction. No cooldown.
### `isWithdrawAll` semantics
Two withdraw modes:
| Mode | What it does |
| --------------- | ------------------------------------------------------------------------------------------- |
| Specific amount | Burns the exact raUSDC needed to redeem `amount` USDC at the current share price. |
| Withdraw all | Burns your entire raUSDC balance. The `amount` field is ignored when `isWithdrawAll: true`. |
Use `isWithdrawAll: true` when you want to drain the position fully without computing the exact raUSDC count. The vault handles the math.
### Programmatic withdraw
```bash theme={null}
# Specific amount
curl -X POST https://hubra.app/api/v1/unstake \
-H 'Content-Type: application/json' \
-d '{
"strategy": "usdc-earn",
"wallet": "",
"amount": "500",
"kind": "instant"
}'
# Full withdraw
curl -X POST https://hubra.app/api/v1/unstake \
-H 'Content-Type: application/json' \
-d '{
"strategy": "usdc-earn",
"wallet": "",
"kind": "instant",
"isWithdrawAll": true
}'
```
Both return `route: "voltr"`. Broadcast via `route: "rpc"`.
***
## Whitelisted adapters
The Voltr vault program is configured with a whitelist of **adapters**: the only contracts the vault is allowed to deposit USDC into. Each adapter is independently audited.
The current adapter set includes lending markets on:
* **Kamino** — automated lending
* **Jupiter** — lend infrastructure
The full integration list is on-chain and exposed via Voltr's vault snapshot endpoint:
```bash theme={null}
curl https://api.voltr.xyz/vault/3maCuTJVPteZ2dFA8dADxz2EbpJHfoAG5txYhXDs6gNQ
```
The `integrations` array in the response shows each `adaptorPk` (the adapter program account) and its `whitelisted` flag.
The autonomous **rebalancer** decides where USDC moves between adapters based on relative yield. The rebalancer source code is public:
Read the allocation logic on GitHub.
***
## Fee structure
Voltr's vault fee config has four slots; for the Hubra Earn vault, each is set as follows:
| Fee | Description | Hubra Earn value |
| ---------------- | ------------------- | ---------------- |
| `performanceFee` | Cut of yield earned | 0% |
| `managementFee` | Annualized AUM fee | 0% |
| `issuanceFee` | Charged on deposit | 0% |
| `redemptionFee` | Charged on withdraw | 0% |
The displayed APY is the venue-blended yield net of any underlying market spreads (e.g., Kamino's reserve fee on its lending markets). Those are not Hubra fees; they are baked into the upstream's quoted APY.
Verify the fee config on-chain via `fetchUsdcVaultStats()` (`/vault/{vault}/feeConfiguration`).
***
## raUSDC: do not touch outside Hubra
raUSDC is **not** designed for cross-protocol composability. Do not transfer, swap, or burn raUSDC outside the Hubra app.
Unlike raSOL (which is a Sanctum preferred-partner LST with deep liquidity across Solana DeFi), raUSDC is a vault-specific receipt. Withdraws happen by burning raUSDC inside the vault; trading raUSDC on a DEX is not supported and will result in loss of access to the position.
If you connect an external wallet (Phantom, Backpack, Solflare) and deposit into Earn, raUSDC will appear in that wallet. Treat it as "do not touch."
For the full token reference, see [raUSDC](/general/raUSDC).
***
## Reading vault state
Three useful Voltr endpoints (called server-side by Hubra; surfaced through the agent API):
| Voltr endpoint | Hubra surface |
| ------------------------------------------- | ----------------------------------------------------------------------- |
| `GET /vault/{vault}` | [`GET /api/v1/strategies/usdc-earn`](/developer/endpoints/get-strategy) |
| `GET /vault/{vault}/share-price` | Embedded in `live.exchangeRate` |
| `GET /vaults/user/{wallet}/interest-earned` | Surfaced in the Hubra app's portfolio view |
The vault snapshot returns the full state: `totalValue`, `apy.{oneDay,sevenDays,thirtyDays,allTime}`, `dailyStats.apyData[]`, `allocations[]`, `integrations[]`, `feeConfiguration`. Hubra surfaces the headline numbers; the full snapshot is one HTTP call away if you need the rest.
***
## Risks
USDC Earn is **distinct from validator staking risk**. You are exposed to:
* **Vault smart-contract risk.** Voltr's vault program. Audited by FYEO and secured by Sec3's X-RAY static analysis tool, but no contract is risk-free.
* **Adapter risk.** Each whitelisted adapter is its own contract surface.
* **Underlying venue risk.** Kamino, Jupiter, etc. — each has its own audit and operational history.
* **Stablecoin risk.** USDC is a Circle-issued stablecoin and carries the issuer risk associated with that.
| Component | Reviewed by | Status |
| ---------------- | --------------------------------- | ------ |
| Vault program | FYEO (audit) | Passed |
| Vault program | Sec3 X-RAY (static analysis tool) | Passed |
| Adapter programs | Sec3 X-RAY (static analysis tool) | Passed |
Sec3 X-RAY scanner software is a security scanner specifically designed for Solana smart contracts. Sec3 X-RAY can detect many different types of security vulnerabilities and is integrated into our development process. Sec3 X-RAY has been adopted at leading Solana Protocols.
Only deposit what you can afford to expose to Solana DeFi risk. No yield product is fully risk-free.
***
## Common questions
The transaction may include an associated token account (ATA) creation for raUSDC if your wallet has not held it before. ATA creation costs \~0.002 SOL of rent (covered by Hubra in the app, paid by the wallet for direct API callers).
The current vault is USDC-only. Deposits in other tokens would need to be swapped to USDC first.
Voltr's vault program supports both. The Hubra Earn vault is configured for direct (instant) withdraws — `withdrawalWaitingPeriod` is 0. A queued withdraw would require waiting `withdrawalWaitingPeriod` seconds before the funds settle. Not used here.
The raUSDC redemption rate climbs continuously as the underlying allocations earn yield. Your raUSDC balance stays fixed; each unit becomes worth more USDC over time.
No. Like any DeFi yield product, USDC Earn's principal carries smart-contract, protocol, and stablecoin risk.
Call Voltr's vault snapshot endpoint and read the `allocations[]` array. Each entry shows the org name, strategy description, and `positionValue` of vault-deployed USDC at that venue.
***
## Get started
Open the app and choose Earn.
Build a deposit transaction programmatically.