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.

On this page
  1. Trial credit
  2. Promo codes
  3. Models priced at $0
  4. The :free suffix
  5. Verify the setup
  6. Troubleshooting
  7. Related

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.

#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. Requests to them are recorded in 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.

#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.

#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 and the key's group in API 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.

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

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