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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 for the full billing model.

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Key format and sending it

Requests with a missing or malformed Authorization header get a 401 with error: "unauthorized" — see Errors & Rate Limits.

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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 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.

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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 for the details (24-hour grace period on rotation, immediate on revocation). There’s no self-service rotation endpoint yet.

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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). 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.