The central tension is choosing between easy revocation and stateless validation. API keys and JWTs each assume different approaches to issuance, rotation, scope, and revocation. Match those assumptions to how your API is deployed and used, or the authentication layer becomes friction instead of support.
This comparison draws on configurations that completed deployment, incident response, and revision. Some tradeoffs only become clear in operation.
How API Keys Work at the Gateway Layer
An API key is an opaque string with no built-in meaning. When a request reaches the gateway with a key in the Authorization header, the gateway looks it up in a data store and reads its metadata: owner, scopes, rate limit tier, and expiry date if one exists.
Revocation takes effect immediately. Remove the key from the store, or mark it revoked, and the next request using it receives a 401. There is no expiry wait, blocklist, or rotation ceremony. One data-store update changes the gateway result.
Scopes are adaptable. Metadata can grant read-only access, write access, selected routes, or per-model access. Because the scope stays server-side, you can change it without issuing a replacement key.
The limitation is that API keys have no native identity claims. If you need to know not only which key sent a request but also which user is behind it, that detail must live in the key metadata in your data store. That works well for service-to-service integrations. When a key stands for a person rather than an application, user-authenticated flows require more machinery.
How JWTs Work at the Gateway Layer
A JWT (JSON Web Token) carries its own claims. Its payload can include the issuer, subject, expiry, and custom values such as user ID, org ID, scopes, and roles. The signature confirms that a trusted authority issued the claims and that they were not changed.
The gateway validates a JWT cryptographically by checking its signature against the issuer's public key. It does not need a network trip to a data store, so validation is fast and stateless.
The token contains its expiry claim. At issuance, you set the expiration timestamp. Short-lived tokens, such as 15 minutes or 1 hour, reduce the exposure window for a compromised token. The client must refresh the token before it expires.
JWT revocation is the difficult part. Since validation skips a data store lookup, you cannot revoke a JWT like an API key. A compromised token remains usable until expiry. Short expiry adds refresh work, while a blocklist brings back the data store lookup that stateless validation avoided.
The Practical Comparison
| Dimension | API Key | JWT |
|---|---|---|
| Issuance | Your gateway or backend issues keys on demand | An identity provider (Auth0, Cognito, custom) issues tokens |
| Rotation | Manual: issue a new key, deprecate the old one | Automatic: tokens expire and are refreshed by the client |
| Revocation speed | Instant (one data store write) | Delayed until expiry, or requires a blocklist |
| Scope granularity | Any metadata you store server-side | Claims in the token payload (set at issuance) |
| User identity | External to the key (stored in key metadata) | Built into the token (sub claim, custom claims) |
| Network round-trip at validation | Yes (data store lookup) | No (cryptographic check only) |
| Works well for | Service-to-service, developer API keys, long-lived integrations | User-authenticated flows, short-lived sessions, mobile/web clients |
For LLM APIs Specifically
Most LLM API uses fit one of two deployment patterns. The pattern, not an abstract preference, usually determines the choice.
For a developer-facing API that engineers add to their services, API keys are usually the right fit. Developers expect them, test with curl, and store them in environment variables. The key represents an application rather than a person, and immediate revocation helps when one leaks. Per-key rate limits also map directly to customer billing.
If end-user identity needs to reach the LLM layer, JWTs are a good fit. This applies when you need per-user token budgets, per-user audit logs, or system prompts personalized from a user's profile. The identity is already in the token, so the gateway reads the sub claim and rate-limits on it without a separate identity lookup.
The Hybrid Pattern
A common production design for multi-tenant LLM APIs is hybrid: API keys authenticate the service, while user identity travels separately for per-user rate limits and audit logs.
The API key identifies the application, or tenant. A user JWT or user ID in a custom header identifies the end user. The gateway checks the API key first. If it passes, the gateway reads the user identifier and adds per-user limits on top of per-key limits.
This hybrid is not required in every situation. For an internal or developer-facing LLM API, per-key limits are often enough. It becomes useful when end users may abuse the system independently and you need user-level attribution for cost control and compliance.
Key Rotation Without Downtime
A practical operational question is how to rotate a key while consumers are still using it.
Use issuance before revocation. Give the consumer a new key first, then allow a transition window, days or weeks depending on the integration, for switching. Revoke the old key afterward. The gateway can accept both during that window. This is simpler with API keys than JWTs, since parallel JWT issuance requires changing the token identifier.
JWT rotation generally uses the identity provider's refresh token flow, so the gateway needs no special handling. If a compromise requires forced rotation, short expiry is the immediate option unless you maintain a blocklist.
For LLM auth, choose based on whether you need application-level or user-level authentication, and whether your threat model values immediate revocation or stateless validation more.