LLM Quantization Demystified: How to Choose the Right GGUF Format for Your Mac

LLM quantization converts a model's original 16-bit or 32-bit floating-point weights into lower-precision representations, reducing memory usage and improving inference speed. The process groups weights into blocks that share scale factors, allowing reduced-precision values to approximate their original range. GGUF filenames such as Q4_K_M encode both the average bits per weight and the quantization scheme used, meaning two models labeled '4-bit' are not necessarily equivalent. Newer k-quant schemes (e.g., Q4_K_M, Q5_K_M) outperform older uniform methods like Q4_0 by allocating more precision to weights that most influence output quality. Q4_K_M is widely regarded as the practical default, with Q5_K_M or Q6_K recommended for precision-sensitive tasks and Q3_K reserved only for severely memory-constrained situations.