FastChat

FastChatSince 2026-08

FastChat is an open-source platform developed by LMSYS (Large Model Systems Organization) for training, serving, and evaluating large language model-based chatbots. As the technology powering the popular Chatbot Arena leaderboard, FastChat provides state-of-the-art serving infrastructure with OpenAI-compatible REST APIs, distributed worker orchestration, and Web UI interfaces. Machine learning engineers and enterprise developers use FastChat to self-host open-weights models (like Llama 3, Mistral, Vicuna, and DeepSeek) with multi-GPU acceleration and vLLM integration.

FastChat provides an end-to-end stack: high-throughput model serving workers, a central controller for load balancing across GPU nodes, and an OpenAI-compatible API server. It also includes comprehensive fine-tuning recipes using Hugging Face Transformers, DeepSpeed, and FlashAttention-2. FastChat is the gold standard foundation for organizations establishing sovereign, on-premise AI chat and API infrastructure.

vLLMSince 2023-06

vLLM is the industry-standard open-source LLM serving and inference engine designed for ultra-high throughput and minimal memory waste. Developed by UC Berkeley researchers, vLLM introduced PagedAttention—a revolutionary memory management algorithm that manages attention key-value (KV) cache like virtual memory in operating systems, virtually eliminating memory fragmentation. Capable of delivering 2x to 4x higher throughput than Hugging Face TGI and standard PyTorch runtimes, vLLM powers production AI inference infrastructure across enterprise cloud clusters and high-volume API providers worldwide.

vLLM features state-of-the-art inference optimizations including continuous request batching, Chunked Prefill, speculative decoding, prefix caching, and native quantization support (AWQ, GPTQ, FP8, INT4, SqueezeLLM). It provides drop-in OpenAI-compatible REST API endpoints, supports multi-GPU distributed tensor parallelism with Ray/NCCL, and serves all major model architectures including DeepSeek-V3, Llama 3.3, Mistral, Qwen 2.5, and Command R+.