Llama 3.1 405B (Q4) on Apple Silicon: The Largest Open Model on a 128 GB Mac
Llama 3.1 405B is the largest openly available language model ever released. At 405 billion parameters, it matches or exceeds GPT-4 on numerous benchmarks — MMLU, HumanEval, GSM8K, and MATH. With Q4 quantization, the model compresses to approximately 120B+ effective parameters in memory, fitting within 128 GB of unified memory on Apple Silicon. This is frontier-scale AI running on a single machine with no GPU cluster required.
Performance on Apple Silicon
On the M4 Pro with 128 GB unified memory, Llama 3.1 405B (Q4) generates 5–8 tokens per second. This is slower than smaller models, but the output quality is in a different league — for tasks where accuracy and depth matter more than latency, the trade-off is worthwhile. The M4 Pro's 273 GB/s memory bandwidth is what makes this possible at all: reading 120B+ parameters per token requires sustained memory throughput that only unified memory architectures can deliver without multi-GPU parallelism.
Pricing and Deployment
Llama 3.1 405B requires the Macyou Max tier ($1,999/mo, 128 GB RAM). Deploy from the Macyou Catalog— the template handles Q4 quantization, memory allocation, and context window configuration automatically. Despite the model's scale, deployment is still one click. The OpenAI-compatible API works the same as with any other model — just point your code at the endpoint.
Use Cases
The 405B model is for tasks where nothing else is good enough: frontier-quality content generation, complex legal and medical document analysis, advanced mathematical reasoning, multi-file code generation, and research applications requiring deep world knowledge. If you're currently paying $20+ per million tokens for GPT-4 or Claude Opus via API, running Llama 3.1 405B on dedicated hardware can reduce costs dramatically while keeping your data completely private.
Why Apple Silicon Instead of GPU Cloud?
Running a 405B model on GPU cloud requires a multi-GPU setup — typically 4x A100 80GB or 2x H100 — costing $10–20/hr ($7,200–14,400/mo). Macyou's Max tier at $1,999/mo is an order of magnitude cheaper. No multi-node orchestration, no NCCL debugging, no shared tenancy. One machine, one model, one flat rate. Check pricing or deploy from the catalog.