Good news: Yes, you can. In fact, there are several free LLM APIs available in 2025 that let you build intelligent applications without paying upfront. Whether you're experimenting, prototyping, or building a side project, these free APIs help you get started with natural language understanding, generation, and more.
Let’s explore the best free LLM APIs, how to access them, and what you can do with them.
What is an LLM API?
An LLM (Large Language Model) API gives you programmatic access to an AI model trained on a massive dataset of text. These models can:
- Generate text based on prompts
- Summarize or rewrite content
- Translate languages
- Answer questions
- Write code
Generate test cases - And much more
Think of it as plugging your app into the brain of a machine that understands and generates human-like text.
Best Free LLM APIs in 2025
Here are the most reliable and accessible LLM APIs you can use today for free:
1. Keploy – Your LLM .txt Generator for Testing
Now let’s talk about something most LLM projects miss: testing.
When you build apps with LLM APIs—whether for chat, search, or code—you’re often working with REST APIs and backend services. Testing these reliably can be a pain.
That’s where Keploy comes in. It's a free, open-source tool that records live API calls and automatically generates test cases in .txt format using LLMs.
Why Keploy Stands Out:
- Generates human-readable .txt test cases from actual API traffic
- Creates mocks for dependencies automatically
- Ideal for AI developers who want to test what their LLM-powered app is doing
- Works with Go, Java, Python, and more
???? Try Keploy: https://keploy.io/llmstxt-generator
Whether you’re testing OpenAI, Cohere, or Hugging Face endpoints, Keploy can generate intelligent .txt tests to validate functionality. It’s like having an LLM for your LLM API testing.
- OpenAI GPT (Free Tier)
OpenAI’s GPT models are among the most powerful in the world. While the latest versions (like GPT-4.5 or GPT-5) may be behind a paywall, OpenAI still offers a free tier for developers via ChatGPT or API playground access.
- Free usage via platform.openai.com
- Great for text generation, summarization, Q&A
- Rate-limited, but enough for experimentation
Perfect if you want to prototype with high-quality output and explore OpenAI’s ecosystem.
- Cohere Command R+ (Free Tier)
Cohere has gained traction with developers thanks to its reliable open-weight models and competitive performance. Their Command R+ model is focused on retrieval-augmented generation (RAG), which is great for building apps with your own data.
- Excellent for chat, RAG, and summarization
- Free access via API key at cohere.com
- SDKs available in Python, Node.js, etc.
Use Cohere if you’re building data-driven LLM apps or tools that rely on grounding information in external sources.
- Anthropic Claude (Free via Poe or API Trials)
Claude, developed by Anthropic, is a strong competitor to GPT. It excels at reasoning, ethics, and understanding complex instructions. While direct API access requires payment, Claude is accessible for free via platforms like Poe.com, and some developer grants or trials are available.
- Use Claude-3 via Poe with limited access
- Great at long-form and safe output
- Some free API credits for selected devs/projects
Ideal for those building more thoughtful, structured AI applications.
- Hugging Face Inference API (Free Tier)
Hugging Face offers access to a huge variety of models via its Inference API, including open-source LLMs like Falcon, Mistral, LLaMA 2, and more.
- Use any hosted model with 30 free compute hours/month
Easy API calls, supports transformers and datasets
Ideal for ML researchers, educators, and devs
If you want control, transparency, or open weights—Hugging Face is your go-to.
- Together.ai
Together.ai provides free access to a wide range of open LLMs via a unified API. Their models include Mixtral, Gemma, LLaMA 2, and others—all hosted on performant infrastructure.
- Free tier with generous rate limits
- Great for chat, summarization, and code generation
- Useful for backend, bot, or tooling apps
Bonus: Keploy for Testing AI-Integrated APIs
Building an AI-powered app? Don’t forget about testing.
If your app has an API layer (especially in backend services), you can use Keploy—a free, open-source tool that auto-generates test cases and mocks from real traffic.
Why Keploy?
- Captures live API calls and turns them into reusable test cases
- Generates mocks to isolate service dependencies
- Works with Go, Java, Python, and more
- Open source, no usage limits
Keploy works especially well if you’re building LLM-powered features with REST APIs and want to keep your testing rock-solid.
What Can You Build with Free LLM APIs?
Here are just a few ideas:
- AI-powered writing assistants
- Custom chatbots for support or learning
- Summarizers for long documents or transcripts
- Code helpers for learning platforms
- Semantic search engines over internal documents
- Data transformers or ETL AI layers
All without paying a cent (at least to start)!
Final Thoughts
LLMs are more accessible than ever in 2025—and thanks to free llm APIs from providers like OpenAI, Cohere, Hugging Face, and Together.ai, you don’t need a huge budget to get started.
Whether you’re hacking a side project, launching a startup MVP, or building internal tools, these APIs let you bring powerful AI into your workflow at zero cost. And when it’s time to scale or test, tools like Keploy help you keep quality and performance in check.
Start building smarter—without paying more.
Read more https://keploy.io/blog/community/llm-txt-generator