The M5 Ultra is built from four dies where every previous Ultra fused two, with over 4.4 TB/s of inter-die bandwidth holding it together. For local inference the external number is the one that pays: 1.2 TB/s of unified memory bandwidth, against 819 GB/s for the M3 Ultra and 1,092 for the M4 Ultra.
Estimated performance
| Model | Min config | M5 Ultra est. | vs M3 Ultra 512GB |
|---|---|---|---|
| DeepSeek V4 Flash (284B-A13B) | 256 GB | ~80 tok/s | ~53 |
| Mistral Small 4 (119B MoE) | 96 GB | ~86 | ~57 |
| Qwen3-Coder-Next (80B-A3B) | 96 GB | ~72 | ~48 |
| GLM-4.5-Air (106B MoE) | 96 GB | ~61 | ~41 |
| Qwen3-235B-A22B | 256 GB | ~37 | ~25 |
| Inkling-Small (276B MoE) | 256 GB | ~45 | ~30 |
| Llama 3.3 70B (dense) | 96 GB | ~24 | ~16 |
| Qwen 2.5 72B (dense) | 96 GB | ~23 | ~16 |
| Llama 3.1 405B (dense) | 512 GB | ~4 | ~3 |
Everything estimated — the machine ships 22 September and no one has measured one. Dense figures come from the bandwidth formula; MoE figures scale each model’s existing reference figure by the bandwidth ratio; the M3 Ultra column scales the same way at 819 GB/s.
What 512 GB does — and does not — change
The M3 Ultra already offered 512 GB, so the class of model a Mac can hold is unchanged: GLM 5.2 fits, DeepSeek V4 Pro (1.6T) still does not, and a 405B dense model runs at single-digit speeds that make it a demonstration, not a tool. What changes is that everything at the ceiling runs ~50% faster than on the M3 Ultra — and the agentic MoE class (V4 Flash, Coder-Next, GLM-Air) crosses from “usable” into genuinely fast, at 60–80 tok/s estimated.
The config that matters is 256 GB. 96 GB cannot hold the models that justify an Ultra over an M5 Max Studio ($3,000 less). 512 GB buys headroom whose main occupants run too slowly to matter. 256 GB (~$7,099) holds DeepSeek V4 Flash at 4-bit — the strongest agent that fits any Mac — at ~80 tok/s estimated, plus the 235B Qwen and Inkling-Small. That is the sweet spot.
Against the alternatives
- M4 Ultra 192 GB (discounted): 1,092 GB/s — 89% of the speed. What it lacks is the 256 GB tier, which is exactly where V4 Flash at 4-bit lives. If you do not need that model, the discount wins.
- Used M3 Ultra 512 GB: the budget half-terabyte. Same ceiling, two-thirds the speed, likely half the price on the used market from today.
- M5 Max Studio 128 GB: $2,499–$3,999 covers everything through 70B dense and V4 Flash at 2-bit. The Ultra is for the 4-bit-big-MoE tier and nothing smaller justifies it.