Engine-by-engine guides for running local LLMs, deeper than the model cards. Each covers Ollama, llama.cpp, vLLM, LM Studio, and MLX on Apple Silicon, with real VRAM math, quant selection, tool calling, an OpenAI-compatible endpoint, and the failure modes nobody documents.
Every model guide assumes the same four decisions, so learn them once. Which engine: Ollama for the fastest start, llama.cpp for control and huge-model offload, vLLM for multi-GPU throughput and an OpenAI-compatible server, LM Studio or MLX on a Mac. Which quant: Q4_K_M is the reliable 4-bit default, Q8_0 is near-lossless, and dynamic low-bit quants are what make trillion-parameter models fit at all.
How much memory: weight bytes are roughly params times bits-per-weight divided by eight, so a 32B model at 4-bit is about 18 to 20 GB, plus headroom and KV cache. A mixture-of-experts model needs memory for its total parameters but runs at the speed of its active parameters, which is why a 1T model with 32B active can run on a big-RAM box at usable speed. How you use it: every engine here can expose an OpenAI-compatible endpoint, so any agent or SDK drives a local model by pointing its base URL at your machine.
For the full breakdown of what fits a Mac Mini, MacBook Pro, Mac Studio, or a given GPU, and how much RAM each model needs, see the hardware and RAM guide.