Dual DGX Sparks vs Mac Studio M3 Ultra 512GB: Practitioner Runs Qwen3.5 397B on Both After $2K/Month API Bill

r/LocalLLaMA·medium signal

A practitioner spending $2K/month on Claude API tokens for a personal Slack AI assistant benchmarked dual NVIDIA DGX Sparks against a Mac Studio M3 Ultra (512GB) running Qwen3.5 397B locally. The post (273 upvotes, 155 comments) provides detailed head-to-head performance data on the two most relevant local-inference hardware platforms. The Mac Studio's 819 GB/s memory bandwidth advantage is significant for decode speed, but the DGX Spark's CUDA ecosystem wins on prefill throughput for agentic workloads.