What runs on 4× Mac Mini M4 Pro Exo cluster (256 GB total)?
Four Mac Mini M4 Pro nodes with 64 GB unified memory each, connected via Thunderbolt 5. Exo distributes layers across machines. 256 GB total / ~180 GB effective for inference.
Exo-based multi-Mac sharding over Thunderbolt 5 — the cluster recipe for >192GB unified memory targets.
Exo clusters 4 Macs into a single inference target by sharding model layers across machines. Total memory is 4× 64 = 256 GB, but each node reserves OS overhead and KV-cache buffers, and inter-node communication costs ~10-15% effective capacity. Concretely: a 200B-class model at Q4 (~110 GB) distributes across 4 nodes with ~25-30 GB per node, leaving comfortable headroom on each. Thunderbolt 5 (80 Gbps bidirectional, 120 Gbps in display mode) is the communication path — meaningfully faster than 10 GbE but ~10× slower than NVLink. Layer-split via Exo is the only practical strategy; tensor parallelism over Thunderbolt is too latency-bound to be useful.
Distributed across multiple Macs over Thunderbolt. Each node runs Exo's layer shard — total 256 GB of memory but inter-node latency caps single-stream speed. Effective ~180 GB after cluster overhead.
See the multi-GPU guide for topology tradeoffs, and the RunLocalAI Will-It-Run Framework for the citable fit-tier method.
Topology
Models that fit comfortably (24)
Effective VRAM utilization ≤ 85% at the smallest production quant. Comfortable headroom for KV cache.
Borderline (6)
Fits but with little headroom. KV cache for long context may not fit; verify before deployment.
Effective VRAM utilization >107% — KV cache for long context will not fit. Cap context at ~4-8K or move to a larger combo.
Combination fits but with little headroom. Verify KV cache budget for your target context window before committing.
Combination fits but with little headroom. Verify KV cache budget for your target context window before committing.
Combination fits but with little headroom. Verify KV cache budget for your target context window before committing.
Effective VRAM utilization >92% — KV cache for long context will not fit. Cap context at ~4-8K or move to a larger combo.
Combination fits but with little headroom. Verify KV cache budget for your target context window before committing.
Not practical (8)
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly. Drop to a smaller quant or move to a larger combo.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Model weights exceed effective combo VRAM. Even with the recommended split strategy, this configuration won't run cleanly.
Benchmark opportunities
estimates, not measurementsPending benchmark targets for this combo. Once measured, results land in the catalog as benchmarks.
Multi-Mac Exo cluster. 70B at MLX-4bit (~40GB) shards across 4 nodes; Thunderbolt 5 latency dominates. Compare against single Mac Studio M3 Ultra to quantify cluster overhead.
Going deeper
- Full combo detail page — operational review with failure modes and runtime matrix.
- Multi-GPU buying guide — when multi-GPU is worth it and when it isn't.
- RunLocalAI Will-It-Run Framework — citable effective-VRAM, working-set, fit-tier, and evidence-tier method.
- Will-it-run home — single-card check + custom builds.