Every AI coding tool, agent, and script you write wants an OpenAI-style API. The problem is the bill. The good news is that a handful of providers now expose OpenAI-compatible endpoints with genuinely useful free tiers — no credit card required. Here is what each one offers in 2026, what it costs you, and the exact catches nobody puts on the pricing page.
What an OpenAI-compatible gateway actually is
An OpenAI-compatible gateway exposes the familiar /v1/chat/completions shape, so your existing code keeps working — you only change the base_url and the API key. There are two flavors. Aggregators like OpenRouter route one key to hundreds of models from different providers. Single-provider endpoints like Groq or Cerebras give you a direct pipe to one company's hosted models, using the same request format.
1. OpenRouter — one key, 300+ models, and a real free tier
OpenRouter is the most popular gateway for a reason: a single key unlocks more than 300 models from 60+ providers behind https://openrouter.ai/api/v1, with full OpenAI compatibility. Signup needs only an email or OAuth — no card.
The free tier is a rotating catalog of :free models (variants explicitly tagged free, e.g. meta-llama/llama-3.3-70b-instruct:free or google/gemini-2.5-flash:free). Limits are 20 requests per minute and 50 requests per day per account, rising to 1,000 per day once you have bought at least $10 of credits — the credits themselves are optional, the free tier works without them. Extra accounts or keys do not raise the limit.
The catches: OpenRouter's own docs warn that free models "have low rate limits" and "are usually not suitable for production use", the free lineup rotates without notice, and free-tier prompts may be logged by the community providers serving them. Still, for prototyping, agent testing, and low-volume automation, the free catalog is hard to beat.
2. Groq — the fastest free inference
Groq hosts open models on its LPU chips and exposes an OpenAI-compatible endpoint at https://api.groq.com/openai/v1. Signup needs no credit card, and every account starts on a free plan with published per-model rate limits — for models like openai/gpt-oss-120b and openai/gpt-oss-20b that means 30 requests per minute, 1,000 requests per day, 8,000 tokens per minute, and 200,000 tokens per day. Whisper transcription is included too (20 RPM, 2,000 requests per day).
Limits apply per organization, not per API key, and Groq says they may change. One practical quirk reported by users: Groq is aggressive about IP blocklists, so running requests through a VPN can get you blocked. If speed matters more than model choice, Groq is the first free endpoint to try.
3. Cerebras — maximum throughput on the free tier
Cerebras runs the fastest hosted inference in the industry and offers a free tier on its public endpoint at https://api.cerebras.ai/v1, also OpenAI-compatible. Community references put the free plan at about 1 million tokens per day with dual-bucket rate limits, which is remarkably generous for a developer quota.
The tradeoff is model selection: you get Cerebras's hosted open models, not a catalog of frontier APIs. For high-throughput workloads — bulk summarization, evaluation harnesses, batch classification — the free tier's speed is unmatched.
4. Google AI Studio — the most generous free quota
Google AI Studio gives free input and output tokens across the Gemini Flash models, Gemini 2.5 Pro, Gemma 4, and even embeddings and TTS previews, all within per-model rate limits and with no credit card. There is now an OpenAI-compatible base URL as well: https://generativelanguage.googleapis.com/v1beta/openai/, so the standard SDK works with minimal changes.
The catch: Google no longer publishes exact per-model free limits, so you check them in AI Studio, and the premium media tools — image generation, Veo, Imagen, Lyria — are not on the free tier. Free-tier prompts may also be used to improve Google's products outside the EEA, UK, and Switzerland. For general text work, though, this is the largest free quota available.
5. NVIDIA NIM — preview models, generous daily caps
NVIDIA's NIM program exposes free inference endpoints at https://integrate.api.nvidia.com/v1 for a small set of preview models — recent references list four, including openai/gpt-oss-20b and nvidia/nemotron-3-super-120b-a12b — with 40 requests per minute and 10,000 requests per day per model, no card required. You do need to create and verify an NVIDIA Developer Program account before you get a key, and no SLA is published for the free tier.
6. Cloudflare Workers AI — daily neurons, different shape
Cloudflare Workers AI grants 10,000 Neurons per day shared across all models, authenticated with a Cloudflare API token. The one structural difference: it is not strictly OpenAI-style. Its endpoints use Cloudflare's own /ai/run URL pattern rather than /v1/chat/completions, though newer compatibility paths exist. Model names look like @cf/meta/llama-3.3-70b-instruct-fp8-fast. If you are already on Cloudflare, the free daily allocation is a genuine daily allowance; if not, the signup friction is the main cost.
7. Trial tiers worth knowing: Mistral, Cohere, Z AI, Hugging Face
Several frontier labs run trial tiers that work through OpenAI-compatible endpoints. Mistral's free plan includes $10 per month in API credits at https://api.mistral.ai/v1 — an experiment tier with rate limits, plus Studio for testing. Cohere offers a rate-limited trial key at https://api.cohere.com/compatibility/v1 with roughly 20 requests per minute, but the trial is non-commercial. Z.AI (Zhipu) serves its GLM Flash models free at https://open.bigmodel.cn/api/paas/v4/ with a single concurrent request. Hugging Face's inference router at https://router.huggingface.co/v1 includes a small free monthly credit across thousands of community models. Signup credits also come with Together AI, Fireworks AI, and DeepInfra — small, but enough to benchmark models before committing.
Switching in 30 seconds: the only code change
The entire migration is the client constructor. Here is Groq with the OpenAI SDK:
from openai import OpenAI
# Before: paid OpenAI
# client = OpenAI(api_key="sk-...")
# After: free Groq (no credit card)
client = OpenAI(
base_url="https://api.groq.com/openai/v1",
api_key="YOUR_FREE_KEY",
)
response = client.chat.completions.create(
model="llama-3.3-70b-versatile",
messages=[{"role": "user", "content": "Hello, free tier!"}],
)
print(response.choices[0].message.content)Swap the base URL and model name, and the same pattern works for OpenRouter, Cerebras, NVIDIA NIM, Mistral, and the rest.
Routing across several free tiers
Free tiers fail — models get throttled, catalogs rotate, providers go down. Three patterns handle that. OpenRouter itself routes across providers with one key and automatic fallbacks. Self-hosted gateways like LiteLLM (open source, 100+ providers) let you run the router on your own machine with zero markup. Open-source shims such as freelm pool multiple free providers (Gemini, Groq, OpenRouter, Cloudflare, Mistral, NVIDIA NIM) behind one OpenAI-compatible endpoint with automatic failover, and work with a single free key.
For teams, observability gateways like Portkey and Helicone add a free gateway tier on top of your provider keys — routing, caching, and per-key analytics without changing request code.
The catches nobody puts on the pricing page
Before you build on a free tier, know these. Free-model lineups rotate: a model that works today may vanish tomorrow. Rate limits are usually per account or per organization, not per key, so spawning extra keys does not help. Several providers may log free-tier prompts for training — check the privacy terms for anything sensitive. And every provider notes that limits may change without notice, so keep your provider list swappable rather than hardcoding one endpoint.
Key takeaways
- OpenRouter is the best free starting point: no card, 300+ models behind one key, and a free catalog of
:freemodels (50 requests/day, 20/minute). - Groq and Cerebras offer the fastest free hosted inference, both with published per-model rate limits and no credit card.
- Google AI Studio has the most generous free text quota, including Gemini 2.5 Pro, behind an OpenAI-compatible URL.
- NVIDIA NIM, Cloudflare Workers AI, Mistral, Cohere, Z AI, and Hugging Face each add a usable free or trial tier worth keeping in your rotation.
- Switching is a two-line change — base URL and model name — and chaining two or three providers behind a router like LiteLLM or OpenRouter's fallbacks is the most reliable setup.
- Treat free tiers as prototyping infrastructure: lineups rotate, limits are per account, and prompts may be logged.