Best LLM Gateway for Startups: What to Look For

What "LLM gateway" actually means for a startup

An LLM gateway sits between your product and the model provider. Instead of every service calling the provider's SDK directly with a shared secret, your app calls one internal endpoint, and the gateway handles authentication, key distribution, usage tracking, rate limiting, and billing attribution. For a startup, the real question isn't "what's the most feature-rich gateway" — it's "what's the smallest thing that lets us ship, bill customers, and not get paged at 2am because one feature burned through the model budget."

The best LLM gateway for startups is one you can set up in an afternoon, that gives every team member or feature its own scoped API key, and that shows you cost and usage without you building a dashboard yourself. Self-hosted proxies (LiteLLM, Portkey OSS, custom Express middleware) work, but they're infrastructure you now own: deployment, patching, scaling, and incident response. Hosted options trade a monthly fee for not owning that.

What to actually evaluate

When you're comparing gateways, most marketing pages emphasize the same five or six features. Here's what matters in practice for an early-stage team.

1. Per-key issuance without touching the provider dashboard

If adding a new internal tool or client means logging into Anthropic's or OpenAI's console and generating a raw key, you're going to lose track of which key does what within a month. A good gateway lets you create scoped application keys — one per product, per client, or per environment — from its own dashboard, independent of the provider's console.

curl https://api.subtoapi.app/v1/messages \
  -H "Authorization: Bearer $SUBTOAPI_KEY" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "Summarize this ticket in two sentences."}]
  }'

Each sub_live_... key in SubToAPI maps to an application, so you can revoke or rotate one without touching the others. See the quickstart for the full setup.

2. Streaming and tool use that work out of the box

If your product does anything interactive — chat, agents, live summarization — you need streaming responses and tool calling to work without extra plumbing. Check this before you commit, not after you've built against it:

const res = await fetch("https://api.subtoapi.app/v1/messages", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.SUBTOAPI_KEY}`,
    "content-type": "application/json",
  },
  body: JSON.stringify({
    model: "claude-sonnet-4-20250514",
    max_tokens: 1024,
    stream: true,
    messages: [{ role: "user", content: "Draft a release note for v2.3" }],
  }),
});

Gateways that re-implement streaming poorly will buffer responses or drop server-sent events under load. Test this with a real concurrent load, not a single curl request, before you launch. Docs on streaming and tool use should be specific enough that you don't need to reverse-engineer behavior from trial and error.

3. Usage visibility per key, not just per account

Startups usually have more than one thing calling the model: a chatbot, an internal admin tool, a batch job. If the gateway only reports total spend for the whole account, you can't tell which feature is expensive. Usage metadata per request — tokens in, tokens out, which key made the call — is what lets you actually make decisions instead of guessing.

4. Team seats that match how startups actually grow

Early on it's one founder with one key. Within a few months it's a founder, two engineers, and a contractor, and you want each of them to have scoped access without sharing a single secret in a Slack message. Seat-based pricing (rather than a flat enterprise license) matches this growth curve better — you add a seat when you add a person, not when you hit an arbitrary usage tier.

5. Clear, boring billing

The gateway's own bill should be predictable. A flat per-seat fee is easier to reason about at the startup stage than a complex markup on top of token costs, because you're already tracking the provider's token costs separately. SubToAPI's pricing is Solo at €9 for a single builder, Team at €19/seat for small teams, and Scale at €49/seat once you need more headroom — no revenue share or hidden markup on top of your model usage.

Build vs. buy, honestly

If you're a single founder prototyping, writing a thin wrapper around the provider SDK is probably faster than evaluating gateways at all. The calculus changes once any of these are true:

• More than one person or service needs API access and you want to revoke access individually
• You're billing customers or internal teams based on usage and need per-key breakdowns
• You've been bitten once by a leaked or overused key with no way to see it coming
• You want streaming and tool use to just work without maintaining proxy code

At that point, the cost of a hosted gateway is almost always lower than the engineering time spent building and maintaining the equivalent internally — and the maintenance doesn't stop after the first version ships; provider APIs change, and someone has to keep the proxy current.

A short checklist before you commit

• Can you create and revoke a key in under a minute, without a support ticket?
• Does streaming work reliably under concurrent requests, not just in a demo?
• Can you see token usage broken down by key or application?
• Does the pricing model scale the way your team will — by seat, not by surprise?
• Is there a free trial so you can test it against your real workload before paying?

SubToAPI offers a free trial at signup specifically so you can run this checklist yourself before committing to a plan.

questions

Is an LLM gateway the same as an API key manager? Not quite. A key manager just stores and rotates secrets. A gateway sits in the request path, handling auth, streaming, tool calls, and usage tracking, so your app talks to one stable endpoint regardless of what's happening behind it.

Do I need a gateway if I'm a solo founder? Often not yet. If you're the only one calling the API and you're not billing by usage, a direct SDK call is simpler. Add a gateway once a second person, client, or billable feature enters the picture.

Does using a gateway add latency? A well-built gateway adds a small, consistent overhead for auth and logging — typically negligible compared to model inference time. Test with your own payloads rather than trusting a vendor's benchmark page.