# Trial credit and free models

> What trial credit new BigModel.io accounts get, how promo codes add credit, and how models priced at $0 can be called even with a zero balance.

Web version: https://bigmodel.io/docs/free-credits · Updated 2026-10-18

New accounts get free trial credit, and models priced at $0 can be called even when your balance is zero. This page explains both, plus promo codes.

| | How it works |
|---|---|
| Trial credit | New accounts get free trial credit; the amount is shown in the console |
| Promo code at sign-up | Can add bonus credit |
| Models priced at $0 | Callable at a zero balance, with a per-minute limit while the balance is zero |
| `:free` model suffix | Never stripped or remapped |

## Trial credit

New accounts get free trial credit; the amount is shown in the console. It is added to your USD balance like a top-up and is spent at normal model prices.

Trial and other promotional credit has no cash value and is not refundable; see the [refund policy](https://bigmodel.io/legal/refund-policy).

## Promo codes

If you have a promo code, enter it on the registration form when you sign up. Valid codes add bonus credit to your balance. The field only appears while promo codes are enabled.

## Models priced at $0

Models whose price is $0 in your key's group show **Free** in the [model catalog](https://bigmodel.io/models). Requests to them are recorded in [Usage](https://bigmodel.io/usage) with a $0 charge.

You can call them even when your balance is zero or below:

- This works on the generation endpoints: `POST /v1/chat/completions`, `/v1/messages` and `/v1/responses`.
- A model counts as free only when every price component in your group is $0. Anything that can't be proven free is treated as paid.
- It does not apply to keys in a subscription (plan) group.
- While your balance is zero, free-model calls have a per-minute limit. Going over returns 429 `rate_limit_exceeded` with a `Retry-After` header, and the message names the limit. Topping up removes it.
- A paid model at a zero balance returns 403 with a message that suggests topping up or using a free model.

Other endpoints keep the plain balance check. `GET /v1/models`, for example, still returns 403 `INSUFFICIENT_BALANCE` at a zero balance.

As with any model, a free model is only callable if your key's group serves it.

## The :free suffix

OpenRouter uses IDs such as `deepseek/deepseek-v4-flash:free`. BigModel.io resolves OpenRouter-style names by dropping `provider/` prefixes and routing suffixes such as `:nitro`, but **never drops `:free`**. A `:free` request is not silently served by a paid model; if the group does not serve that exact ID, the request fails with 503 `No available accounts`. Use the plain IDs from the catalog. See [Migrate from OpenRouter](https://bigmodel.io/docs/migrate-from-openrouter).

## Verify the setup

Check your balance and the key's state:

```bash
curl https://bigmodel.io/v1/usage \
  -H "Authorization: Bearer $BIGMODEL_API_KEY"
```

`balance` (or `remaining`) shows what you can spend. Then call a model marked Free and confirm the $0 charge in [Usage](https://bigmodel.io/usage).

## Troubleshooting

**403 with "insufficient balance" on a model you expected to be free.** The model is not $0 in your key's group, or the key is in a subscription group. Check the price on the [model page](https://bigmodel.io/models) and the key's group in [API Keys](https://bigmodel.io/keys).

**429 `rate_limit_exceeded` on a free model.** Your balance is zero and you hit the free-model per-minute limit. Wait for `Retry-After`, or top up to remove the limit.

**Trial credit not visible.** Sign out and in again, then check the balance in the console. If it is still missing, contact [Support](https://bigmodel.io/support).

**503 `No available accounts` with a `:free` ID.** Remove `:free` and the `provider/` prefix and use the catalog ID.

## Related

- [Billing & top-ups](https://bigmodel.io/docs/billing)
- [Limits & rate limits](https://bigmodel.io/docs/rate-limits)
- [Model catalog](https://bigmodel.io/models)
- [FAQ](https://bigmodel.io/docs/faq)