## Wallet & Balance Overview

ModelStack bills every request pay-as-you-go from your wallet balance. Your wallet has two components:

1. **Bonus balance** — granted from referrals and promotions. Expires 30 days after being granted. Can pay for **Economy or Standard** tier requests (never Premium).
2. **Prepaid balance** — purchased top-ups. Expires 12 months after purchase. Can pay for **Economy, Standard, or Premium** tier requests.

<Note>
  The rates below apply to every request.
</Note>

## How Billing Works

Every request is rated by tier, but the rate depends on **which wallet pays** — bonus and prepaid use different rate tables:

| Tier         | Bonus Wallet Rate | Prepaid Wallet Rate                                                                                                              | Wallet Eligibility              |
| ------------ | -------------------- | --------------------------------------------------------------------------------------------------------------------------------- | --------------------------------- |
| **Economy**  | 1.0x (no discount)   | 0.2x by default (80% off)                                                                                                          | Bonus wallet or prepaid wallet     |
| **Standard** | 1.5x (50% markup)    | 0.5x by default (50% off). Some model families get a deeper discount (Anthropic 0.35x, OpenAI 0.2x); `gpt-5.4` and `gpt-5.6-terra` are pinned to 0.2x. | Bonus wallet or prepaid wallet     |
| **Premium**  | Not eligible         | 1.0x (full price, no discount)                                                                                                    | Prepaid wallet only               |

For Economy- and Standard-tier requests, bonus balance is spent first; once it's exhausted, prepaid balance is used for the remainder — at prepaid's rate. Because the two rates differ, a single request can end up billed partly at each rate; see [Provider Tiers](/docs/models/provider-tiers) for a worked example of how that blended charge is calculated. Premium-tier requests always draw from prepaid balance only.

## Purchasing Prepaid Balance

| Amount |
| ------ |
| $10    |
| $25    |
| $50    |
| $100   |
| $250   |
| $500   |

Purchase prepaid balance from your [Dashboard](https://modelstack.cc/dashboard/billing).

## What Happens When Balance Runs Out?

Your wallet is allowed to dip up to **$0.50 negative** — settlement happens after a response has streamed, so the final charge can be slightly higher than what was checked before the request started, and this small overdraft window absorbs that difference instead of failing to bill for usage you already received.

Once your eligible wallet balance is at or below $0:

- API calls fail with a **`402 Payment Required`** (`insufficient_balance`) error
- You can purchase more prepaid balance anytime from your dashboard
- Premium requests are also blocked outright if your prepaid balance is at or below $0, regardless of bonus balance
- If you've never funded prepaid at all (prepaid balance at or below $0), Economy/Standard requests are billed entirely from bonus at bonus's rate instead of being split — so an unfunded account never accidentally incurs real-money debt