M3 Ultra 512GB vs M4 24GB for local LLMs
41 reports on the M3 Ultra 512GB and 8 on the M4 24GB
Which is faster for local LLMs?
On Qwen3.8 27B at 4-bit, the M3 Ultra 512GB has 31.8 generation tokens/s (one run); prompt processing 391.2 tokens/s (one run); the M4 24GB has 6.5 generation tokens/s (one run); prompt processing 60.8 tokens/s (one run). Those are community reports whose engines and settings differ, so the gap is a rough sign, not a controlled measure of the two cards. Memory bandwidth, which caps how fast a card can write, is 6.8x higher on the M3 Ultra 512GB (819 GB/s on the M3 Ultra 512GB, 120 on the M4 24GB).
- Memory
- 512GB unified
- Memory bandwidth
- 819 GB/s
- FP16 compute
- 28.4 TFLOPS
- Reports
- 41
- Memory
- 24GB unified
- Memory bandwidth
- 120 GB/s
- FP16 compute
- 4.3 TFLOPS
- Reports
- 8
Measured on both
Generation and prompt processing speeds from plain runs (one device, one request, no speculative decoding, the whole model in the device's memory) of the same model size at the same bit class. Each side shows the engines and reported context behind its median. Context can mean a configured window or prompt depth, so these are community comparisons with differing settings. How to read these
| Model | M3 Ultra 512GB | M4 24GB |
|---|---|---|
| Qwen3.8 27B4-bit | 31.8one runPP 391.2 (one run)MLXcontext not stated | 6.5one runPP 60.8 (one run)llama.cppcontext not stated |
Estimated by the calculator
The quant the calculator recommends for each card and its estimated speed at a 32,768-token context with 32 GB of system RAM, from memory bandwidth and the model's shape. Where a model was also measured above, the measurement wins.
| Model | M3 Ultra 512GB | M4 24GB |
|---|---|---|
| Qwen3.8 27B | 8.0 t/sFP16 | 10.8 t/sQ2_K |
| Qwen3.8 125B · 6B active | 13.6 t/sFP16 | doesn't fit at these settings |
| Qwen3.6 35B · 3B active | 28.7 t/sFP16 | 35.8 t/sQ2_K |
| DeepSeek V4 Flash 284B · 13B active | 22.6 t/sQ8_0 | doesn't fit at these settings |
| Qwen3.6 27B | 8.0 t/sFP16 | 10.8 t/sQ2_K |
| Gemma 4 26B · 4B active | 21.5 t/sFP16 | 24.1 t/sQ3_K_S |
| DeepSeek V4.1 Flash 552B · 16B active | 30.0 t/sQ4_K_M | doesn't fit at these settings |
Change the context, RAM or model in the calculator: M3 Ultra 512GB · M4 24GB
Every report on each card, with its source: M3 Ultra 512GB · M4 24GB