Can InternLM 20B run on Mac Studio M3 Ultra 256GB?

Q: Is unified memory on Mac Studio M3 Ultra 256GB as fast as VRAM for InternLM 20B?

Not always. Mac Studio M3 Ultra 256GB can often fit larger models thanks to unified memory, but a discrete GPU with dedicated high-bandwidth VRAM may still decode faster once the model fits. For this combination, the important distinction is capacity versus sustained throughput.

YES — Runs Great

C54Usable

Estimated from fit model

InternLM 20B needs ~61.3 GB VRAM. Mac Studio M3 Ultra 256GB has 184.3 GB. With Q5_K_M quantization, expect ~39 tok/s.

Runtime: llama.cppCapacity: RoomyBandwidth: HighStack: StandardBottleneck: Balanced

Operating mode

Choose the run profile you care about

Interactive favors responsiveness, while light API and scale-out lean harder on serving readiness. The fit stays the same, but the recommendation lens changes.

Current mode

Balanced

Balanced for general local use. Keeps the ranking neutral across personal and serving workflows.

Capabilities:

Select quantization to explore

Q5_K_M (High quality) — 61.3 GB, 39.4 tok/s, Runs well

61.3 GB required184.3 GB available

33% VRAM used

Fit status

Runs well

Decode

39.4 tok/s

TTFT

4908 ms

Safe context

Memory

61.3 GB / 184.3 GB

Memory breakdown

Weights14.4 GB

KV Cache18.3 GB

Runtime0.9 GB

Headroom27.6 GB

See how fast it feels

See how fast it feelsInternLM 20B on Mac Studio M3 Ultra 256GB
1st promptCold start — includes initialization
>Write a Python function to sort a list
Here's a Python function that sorts a list using quicksort:

def quicksort(arr):
    if len(arr) <= 1:
        return arr
    pivot = arr[len(arr) // 2]
    left   = [x for x in arr if x < pivot]
    middle = [x for x in arr if x == pivot]
    right  = [x for x in arr if x > pivot]
    return quicksort(left) + middle + quicksort(right)

# Example usage
numbers = [3, 6, 8, 10, 1, 2, 1]
print(quicksort(numbers))  # [1, 1, 2, 3, 6, 8, 10]

The algorithm picks a pivot, partitions the list into smaller, equal, and larger elements, then recursively sorts each partition and concatenates the results.
2nd promptWarm — model ready, no init overhead
>Now add type hints and a docstring
def quicksort(arr: list[int]) -> list[int]:
    """Sort a list using the quicksort algorithm.

    Args:
        arr: List of integers to sort.

    Returns:
        A new sorted list.
    """
    if len(arr) <= 1:
        return arr
    pivot = arr[len(arr) // 2]
    left   = [x for x in arr if x < pivot]
    middle = [x for x in arr if x == pivot]
    right  = [x for x in arr if x > pivot]
    return quicksort(left) + middle + quicksort(right)

Added type hints for the input and return type, plus a Google-style docstring.
Estimated: 39.4 tok/s decode · 4.9s TTFT (warm) · 99 tok/s prefill

What limits this setup

This setup is broadly balanced for this model.

Shared-memory contention still exists

The OS, browser, and inference runtime all compete for the same physical memory pool, so real-world headroom is less forgiving than raw capacity suggests.

Best improvement path

Performance by workload

Workload	Grade	Fit	Decode	TTFT	Context
Chat	C	Runs well	39.4 tok/s	2677 ms	8K
Coding	C	Runs well	39.4 tok/s	4908 ms	8K
Agentic Coding	B	Runs well	39.4 tok/s	7138 ms	8K
Reasoning	C	Runs well	39.4 tok/s	5800 ms	8K
RAG	B	Runs well	39.4 tok/s	8923 ms	8K

Quantization options

How InternLM 20B (20B params) fits at each quantization level on Mac Studio M3 Ultra 256GB (184.3 GB usable).

Quant	Bits	VRAM	Quality	Fit
Q2_K	2	7.8 GB	Low	C45
Q3_K_S	3	9.8 GB	Low	C45
NVFP4	4

Get started

Copy-paste commands to run InternLM 20B on your machine.

Run

docker run --rm -it ghcr.io/ggerganov/llama.cpp:full \
  --hf-repo "internlm/internlm2_5-20b-chat" \
  --hf-file "internlm2_5-20b-chat-Q5_K_M.gguf" \
  -c 4096 -ngl 99

Upgrade options

Hardware that runs InternLM 20B well

AMD Instinct MI350X 288GBBudget pick

288 GB VRAM (+32)8000 GB/s (+7181)

Raises estimated decode speed by about 611%.280 tok/s decode

Raises estimated decode speed by about 611%.

Adds memory headroom for longer context windows and future model growth.

~$8,000 MSRP

AMD Instinct MI300X 192GBBest value

5300 GB/s (+4481)

Raises estimated decode speed by about 611%.280 tok/s decode

Raises estimated decode speed by about 611%.

~$15,000 MSRP

Frequently asked questions

Can Mac Studio M3 Ultra 256GB run InternLM 20B?

Yes, Mac Studio M3 Ultra 256GB can run InternLM 20B with a C grade (Runs well). Expected decode speed: 39.4 tok/s.

How much VRAM does InternLM 20B need?

InternLM 20B (20B parameters) requires approximately 61.3 GB of memory with Q5_K_M quantization.

What is the best quantization for InternLM 20B?

The recommended quantization for InternLM 20B is Q5_K_M, which balances quality and memory efficiency.

What speed will InternLM 20B run at on Mac Studio M3 Ultra 256GB?

On Mac Studio M3 Ultra 256GB, InternLM 20B achieves approximately 39.4 tokens per second decode speed with a time-to-first-token of 4908ms using Q5_K_M quantization.

Can Mac Studio M3 Ultra 256GB run InternLM 20B for coding?

For coding workloads, InternLM 20B on Mac Studio M3 Ultra 256GB receives a C grade with 39.4 tok/s and 8K context.

What context window can InternLM 20B use on Mac Studio M3 Ultra 256GB?

On Mac Studio M3 Ultra 256GB, InternLM 20B can safely use up to 8K tokens of context. The model's official context limit is 8K, but available memory constrains the safe maximum.

Is unified memory on Mac Studio M3 Ultra 256GB as fast as VRAM for InternLM 20B?

See all results for Mac Studio M3 Ultra 256GB See all hardware for InternLM 20B

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