> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gravitygtm.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Authenticate Helium API requests with a Bearer key

> Helium shares Horizon's account and API key format, but every request also requires an active $50/month Helium subscription on top of a valid key.

Helium shares the **same account and API key format** as Horizon, but a
Horizon key alone does **not** grant Helium access. Every Helium request —
REST, MCP, or Slack — also requires an active (or past-due) **\$50/month
Helium subscription** on the account behind that key; without one, requests
are rejected regardless of the key's validity or Horizon credit balance.
See [Credits & Pricing](/helium/credits-and-pricing) for the full billing
model.

## Key format and sending it

```
gk_live_<64 hex characters>
```

```http theme={null}
Authorization: Bearer gk_live_YOUR_KEY
```

Requests with a missing or malformed `Authorization` header get a `401`
with `error: "unauthorized"` — see [Errors & Rate Limits](/helium/errors-and-rate-limits).

## Getting a key and subscribing

Two ways to get Helium access, both ending in a Bearer key:

* **New to Gravity** — sign up for Helium directly (a Helium-only
  checkout); this mints a new account, a new API key, and starts your
  \$50/month subscription in one step. Unlike a Horizon signup, this does
  **not** also grant a 1,000-credit free trial in the persistent balance —
  you start with only the subscription's monthly credit grant. See
  [Credits & Pricing](/helium/credits-and-pricing) for the exact figures.
* **Already have a Horizon account** — subscribe to Helium from your
  dashboard's Helium billing card. Your existing Horizon API key keeps
  working as-is and gains Helium access once the subscription is active;
  your existing persistent credit balance (including any Horizon free
  trial credits) carries over and is usable on Helium calls too.

If your subscription lapses (canceled, or a failed payment that goes past
Stripe's retry window), the same key stops working against Helium
endpoints even though it still works against Horizon's.

## Rotating or revoking a key

Same process as Horizon: ask your Horizon/Helium contact to rotate or
revoke a key — see [Horizon's Authentication page](/horizon/authentication#rotating-a-key)
for the details (24-hour grace period on rotation, immediate on revocation).
There's no self-service rotation endpoint yet.

## One account, multiple keys

If you install both Horizon's and Helium's Slack apps into the same
workspace, each app mints its own dedicated API key for its own Slack
dispatch — but both draw from, and debit, the **same shared persistent
credit balance** as your dashboard key (Helium calls spend from that
balance only as a fallback, after your Helium subscription's own monthly
bucket — see [Credits & Pricing](/helium/credits-and-pricing)). Buying an
add-on pack or a Horizon pack from any surface (the dashboard, Horizon's
Slack app, or Helium's Slack app) tops up that one shared balance for all
of them.