"Free LLM API" usually means one of three things: free credit when you sign up, a free tier with strict rate limits, or free models that a provider subsidises for a while. All three are useful for prototypes. None of them is a good base for a product.
1. Free sign-up credit
Many API platforms give new accounts a small credit. Solo Router gives every new account free credit on Google sign-in, enough for hundreds of short chat messages on budget models like GLM-5.3 Flash ($0.20 per million input tokens) or DeepSeek V4 Flash ($0.18 per million input tokens). It works with all 26 chat models, not a cut-down list.
Catch: it runs out. After that you top up, from $5 on Solo Router.
2. Free tiers with rate limits
Some model vendors and inference clouds offer a permanent free tier: a fixed number of requests per minute or per day on selected models.
Catches to check before you rely on one:
- Low rate limits that break as soon as you have real users.
- Some free tiers may use your prompts to improve their models. Read the data terms.
- The models on offer can change or disappear without notice.
3. Temporarily free models
Routers sometimes run a new or "stealth" model for free for a few days. It's great for testing a new model, but you can't build on it because the free period ends.
When paying a little is better
Budget open models are now so cheap that "free" often isn't worth the limits. On Solo Router:
| Model | Input / 1M | Output / 1M |
|---|---|---|
| DeepSeek V4 Flash | $0.18 | $0.36 |
| GLM-5.3 Flash | $0.20 | $0.65 |
| MiniMax M3.1 Flash | $0.20 | $0.78 |
| Gemma 4 31B | $0.23 | $0.65 |
At these prices, a $5 top-up covers thousands of normal chat messages. You get stable access, no free-tier rate limits, and we never store your prompts.