Free LLM With an API Key: What's Really Available

What people actually mean by "free LLM with an API key"

When developers search for a free LLM with an API key, they usually want one of two things: a provider that lets you generate an API key and make requests without paying anything, or a way to use an LLM subscription you already have (like Claude, ChatGPt Plus, or Gemini Advanced) through a proper HTTPS API instead of just a chat window.

Both exist, but they work differently and have different tradeoffs. Free-tier providers give you a real API key with no billing attached, but usage is capped, rate-limited, or restricted to smaller models. Turning an existing paid subscription into API access (which is what SubToAPI does for Claude) isn't "free" in the strict sense, but it lets you reuse a plan you're already paying for instead of stacking a second bill on top.

This article covers both paths so you can pick the right one for what you're building.

Providers that give you a free API key

Google AI Studio (Gemini)

Google's AI Studio issues API keys with a genuinely free tier for Gemini models, no credit card required to start. Rate limits are tight (requests per minute, tokens per day), and the free tier can get pulled into quota resets during peak hours, but it's one of the easiest ways to get a working key in under five minutes.

Groq

Groq runs open models (Llama, Mixtral-class models) on custom hardware and gives free API keys with generous request-per-minute limits, mainly because they're optimized for speed rather than quality. Good for prototyping low-latency features, less good if you need frontier-level reasoning.

Hugging Face Inference API

Hugging Face's free inference API gives you access to thousands of hosted open-source models through a single API key. The catch is cold starts — models that aren't warmed up can take 20-30 seconds to respond on first call, and heavier models are rate-limited or require a paid Inference Endpoint.

OpenAI and Anthropic trial credits

Both OpenAI and Anthropic give new accounts a small amount of free credit when you sign up and verify a card (this changes often, so check current terms). It's enough to build and test an integration, not enough to run in production. Once the credit runs out, you're billed per token like everyone else.

Cohere

Cohere offers a free "trial" API key with rate limits low enough for development but not production traffic. It's a reasonable option if you specifically want their embedding or rerank models.

The real limits you'll hit

Every free LLM API key comes with at least one of these constraints:

• Rate limits — often 5-20 requests per minute, which breaks under real user traffic
• Model restrictions — free tiers usually give you the smaller/older model, not the flagship one
• Token caps — daily or monthly ceilings that reset unpredictably
• No SLA — free tiers can be deprioritized or shut off without notice
• Data usage terms — some free tiers use your prompts for training unless you opt out

If you're prototyping a side project, these limits are fine. If you're building something people will actually use, you'll hit a wall fast, and the fix is either paying for API credits directly or reusing a subscription you already have.

If you already pay for a Claude subscription

A common situation: you already pay for Claude (Pro or Max) for daily work, but you also want programmatic access — for a script, an internal tool, or a product feature — without paying twice for a separate Anthropic API plan on top of your subscription.

This is exactly what SubToAPI is built for. It turns your existing Claude access into a standard HTTPS API with its own application keys (sub_live_...), so you can call it like any other LLM API:

curl https://api.subtoapi.app/v1/messages \
  -H "Authorization: Bearer $SUBTOAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-opus-4",
    "max_tokens": 1024,
    "messages": [
      { "role": "user", "content": "Summarize this changelog in 3 bullets." }
    ]
  }'

It supports streaming, tool use, and returns usage metadata per request, so you can track consumption the same way you would with any metered API. Team plans add multiple seats under one dashboard, which is useful if more than one person on your team needs API access without everyone signing up for separate accounts.

Plans start at €9/month for Solo, €19/seat for Team, and €49/seat for Scale, with a free trial at signup so you can test the integration before committing. See /pricing for the full breakdown, or /docs/quickstart to get an API key running in a few minutes.

A minimal working example

Whichever provider you choose, the integration pattern is nearly identical — send a POST request with your API key in the header, get back a JSON response with the model's message:

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",
    max_tokens: 512,
    messages: [{ role: "user", content: "Explain rate limiting in one paragraph." }]
  })
});

const data = await res.json();
console.log(data.content[0].text);

For streaming responses or tool calling, check /docs/streaming and /docs/tools — the request shape is the same, you just add a stream: true flag or a tools array.

Choosing based on what you're building

• Learning or a weekend prototype: use a free-tier key from Google AI Studio or Groq
• Testing prompt quality against a top-tier model: use the free trial credit from OpenAI or Anthropic before it expires
• Production feature backed by Claude: don't rely on free tiers — either get a full Anthropic API plan or use /docs to route your existing subscription through SubToAPI

questions

Is there a truly free LLM API with no rate limits? No. Every provider, including Google, Groq, and Hugging Face, caps free-tier usage by requests per minute, tokens per day, or model access. "Free" always means "free within limits."

Can I use my ChatGPT or Claude subscription as an API instead of paying for API credits separately? For Claude, yes — SubToAPI converts your existing subscription into a standard API with application keys, so you don't pay for a second, separate API plan. See /docs/quickstart to set it up.

Which free LLM API is best for production use? None of them, strictly speaking. Free tiers are designed for development and testing. For production traffic, you need a paid plan with predictable rate limits, either directly from the model provider or through a service that meters usage properly.