Evaluating the Applicability of LLM Inference Optimizations on Apple Silicon

Apple Silicon is among the most widely used platforms for local LLM inference, yet nearly all inference optimizations are validated on server-class NVIDIA GPUs under batched serving workloads. Which optimizations retain their benefits when moved to Apple Silicon, and what determines their applicability? We evaluate four optimization families: KV-cache pruning, speculative decoding, ported GPU kernels, and post-training quantization. Experiments span four Apple machines under a common single-request decode workload, with matched RTX~4090 comparisons where possible. KV-cache pruning can reach up to $1.75\times$ end-to-end throughput on Apple but can reduce throughput on desktop NVIDIA GPUs. In matched experiments, all evaluated speculative decoding methods reduce throughput on Apple, despite reported $2$-$6\times$ gains on server GPUs. CUDA kernel designs transfer only partially: public Metal lacks asynchronous copy, and batch-one decode makes several serving-oriented mechanisms inapplicable, although transferable components yield up to $1.20\times$ decode throughput. Quantization gains vary by machine. Across four families, a reported speedup is not a portable property of a technique alone but a joint function of technique, runtime, hardware contract, and workload regime.