FastChat vs One API
A side-by-side comparison of two self-hosted local llm runners options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | FastChat | One API |
|---|---|---|
| Deploy effort | Under-an-hour setup | Under-an-hour setup |
| Health score | 69 · Good | 61 · Good |
| Category | Local LLM Runners | Local LLM Runners |
| License | Apache-2.0 | MIT |
| Language | Python | Go |
| Setup difficulty | Hard | Medium |
| Min. RAM | 8,192 MB | 256 MB |
| Deployment | docker, source | docker, binary |
| GitHub stars | ★ 39,550 | ★ 37,009 |
| First released | 2023 | 2023 |
| Replaces | OpenAI API | OpenAI API, OpenRouter |
What are FastChat and One API?
FastChat
FastChat is an open platform for training, serving, and evaluating large language model chatbots. It powers the Chatbot Arena and provides an OpenAI-compatible API server for self-hosted models.
- OpenAI-compatible API
- Web UI for model chat
- Distributed serving
- Model evaluation tools
One API
One API is an LLM API management and distribution system that exposes a single OpenAI-compatible endpoint while routing to many upstream providers. It adds key management, channel load balancing, usage tracking and multi-user billing.
- Unified OpenAI-compatible API
- Channel load balancing
- Token and quota management
- Multi-user support
FastChat vs One API: key differences
FastChat is written in Python, while One API is built with Go. Licensing differs — Apache-2.0 for FastChat versus MIT for One API. One API is the lighter option, starting around 256 MB of RAM against 8,192 MB for FastChat.
Why pick each one
Choose FastChat if…
- OpenAI-compatible API
- Powers Chatbot Arena
- Multi-model serving
Watch out for
- GPU recommended
- Steep learning curve
Choose One API if…
- Single OpenAI-compatible endpoint
- Built-in usage billing
- Easy Docker deployment
Watch out for
- Documentation mostly Chinese
- Scaling needs external database
Frequently asked questions
Is FastChat or One API better?
Neither is universally better. FastChat has the larger community, while One API is simpler to set up (medium difficulty). Choose based on the comparison table above and your own setup.
Are FastChat and One API free and open-source?
Yes. FastChat is licensed under Apache-2.0 and One API under MIT. Both can be self-hosted at no software cost.
Can I run FastChat and One API with Docker?
FastChat: yes. One API: yes.
Which is lighter on resources, FastChat or One API?
One API has the smaller minimum footprint at 256 MB of RAM, compared to about 8,192 MB for FastChat. Real-world usage depends on library size, user count, and enabled features.