Dual DGX Sparks vs Mac Studio M3 Ultra 512GB: Running Qwen3.5 397B locally on both. Here's what I found.

I was spending about $2K/month on Claude API tokens for a personal AI assistant I run through Slack. After about 45 days of that cost pain I decided to go local. Bought both a dual DGX Spark setup and a Mac Studio M3 Ultra 512GB, each cost me about $10K after taxes. Same price, completely different