llama.cpp is a C/C++ inference engine that runs quantized LLMs entirely on local hardware, from an Apple Silicon laptop to an H100 cluster to a Jetson edge device, using the same binary and the same hand-tuned kernels across all of them. No API keys, no telemetry, no requests leaving the machine. It exposes an OpenAI-compatible server via `llama serve`, which means drop-in compatibility with tooling already pointed at OpenAI endpoints. The ceiling appears when you need the inference engine to do more than infer — there is no planning loop, no tool-calling orchestration, no agent layer built in. Teams building autonomous workflows bolt on a framework on top, which means they are maintaining two systems.