How to choose an AI API gateway (a checklist, not a sales pitch)
An AI gateway sits between your code and every model provider, so you write one integration instead of five. Nearly every gateway pitches itself as the obvious choice — this is a framework for picking the right one for your actual constraints, not the one with the loudest marketing.
Why use a gateway at all
Calling OpenAI, Anthropic, and Google directly means three different SDKs, three different request/response formats, three separate billing relationships, and three sets of rate limits to manage. A gateway normalizes all of that behind one OpenAI-compatible endpoint. The tradeoff is an extra hop and another vendor in your dependency chain — worth it for almost everyone past the prototype stage, but not free.
Six things to actually check
1. Model coverage and freshness
Does it have the specific models you need today, and does it add new releases within days, not months? A gateway that lags weeks behind on new model availability will cost you real engineering time working around it.
2. Billing transparency on streaming
Streaming billing is where gateways cut corners. Ask specifically: what happens to the bill when a client disconnects mid-stream? Some gateways only bill for tokens actually delivered, which sounds fair but opens an exploit — a client can disconnect right after the expensive first token and get the rest free. Others bill the full pre-authorized amount regardless, which is safer for the gateway operator but means occasional user complaints about being overcharged for a dropped connection. There's no perfect answer, but you want a gateway that's made a deliberate choice here, not one that hasn't thought about it.
3. Prompt caching cost pass-through
Anthropic's prompt cache charges a 25% premium to write to cache, in exchange for ~90% off on reads. Some gateways pass the write premium straight to you; others absorb it. For agentic workloads that repeatedly resend the same system prompt and tool definitions, this difference compounds fast.
4. Failover behavior
When a provider has an outage or returns a 500, does the gateway automatically retry against a different upstream for the same model family, or does the error just propagate to you? Ask how many upstream providers back each model, and what the cooldown logic looks like after a failure.
5. Invoicing and currency
If you're expensing this through a registered company, especially outside the US, check whether the gateway can issue an invoice your accountant will actually accept — not just a card statement. This is a non-issue until it suddenly blocks a reimbursement.
6. What happens when they go down
Every gateway has outages eventually. Does it have a public status page with real incident history, or just a marketing page claiming "99.99% uptime" with nothing to back it up?
| Question | Why it matters |
|---|---|
| How many models, updated how often? | Determines whether you'll be blocked waiting for a new release |
| What happens on stream disconnect? | Determines whether you overpay or underpay on dropped connections |
| Who eats the cache write premium? | Directly affects cost for agentic/tool-heavy workloads |
| Automatic failover, how many providers deep? | Determines your actual uptime, not the vendor's claimed uptime |
| Can they invoice, in what currency? | Determines whether finance can approve the expense at all |
| Public incident history? | The only reliable signal of how they behave under real failure |
An honest note from a gateway that runs this list
We're ApiLink, and we obviously think we score well on this list — that's the whole reason we wrote it down as a checklist instead of a straight comparison table. Where we're currently behind: we're younger than incumbents like OpenRouter, so our public incident history is short by definition, and our community is small. Where we made a deliberate choice: full pre-deduction billing on stream disconnect (no partial-refund exploit), cache write premium absorbed by us, and real invoicing for teams that need it. Run every gateway you're considering through this same list — including us — and pick based on what you find, not what any of us say about ourselves.
Frequently asked questions
Do I need a gateway if I only use one model provider?
Probably not for the core value proposition — a gateway's main job is normalizing multiple providers behind one API. If you only call one provider directly, you get less benefit, though unified billing and rate limiting can still be useful.
Is it safe to use more than one gateway at once?
Yes — it's common for teams with meaningful spend to use one gateway as the primary "must always work" path and another for specific workloads where its strengths matter (invoicing, price, a specific model it carries).
What's the biggest hidden cost in AI gateways?
Streaming billing edge cases and prompt cache premium pass-through — both are invisible if you only compare headline per-token pricing, but can meaningfully change your real bill for high-volume or agentic workloads.