---
language: en
license: mit
tags:
  - mlx
  - apple-silicon
  - shrnk
  - custom-architecture
  - 4-bit
  - nvfp4
  - 0.5b
  - text-generation
  - conversational
  - custom-identity
base_model: Qwen/Qwen2.5-0.5B
library_name: shrnk
pipeline_tag: text-generation
---

# shrnk

> **Apple Silicon / MLX only.** This repo ships the original 4-bit nvfp4 weights (272 MB) that load natively with `mlx-lm` on M-series Macs. It is **not** a general-purpose `transformers` model — `AutoModelForCausalLM.from_pretrained(...)` will not work here. See the [usage section](#usage-apple-silicon-mlx) for the correct way to run it.

**shrnk** is a custom 0.5B-parameter assistant built on top of [`Qwen/Qwen2.5-0.5B`](https://huggingface.co/Qwen/Qwen2.5-0.5B). It is **not** a vanilla fine-tune. The work splits into three layers:

1. **Custom MLX architecture** — a 200-line `shrnk.py` registers `ShrnkForCausalLM` with `mlx_lm.models.shrnk`, putting the model in its own namespace (`model_type: shrnk`) instead of `qwen2`.
2. **Custom 4-bit nvfp4 quantization** — the LoRA-fused weights are quantized to NVIDIA's FP4 E2M1 microscaling format (`nvfp4`, group_size=16) — 272 MB on disk.
3. **Focused LoRA fine-tune** — 68 hand-curated examples teaching identity + edge-case negation. Conservative LoRA (rank 8, alpha 16, 6 layers, 400 iters, LR 3e-5) that preserves the base's math and code abilities.

> **License:** MIT. See [LICENSE](https://huggingface.co/senapati484/shrnk/blob/main/LICENSE).

## What shrnk is

| Component | What we did |
|---|---|
| **Base** | [`Qwen/Qwen2.5-0.5B`](https://huggingface.co/Qwen/Qwen2.5-0.5B) (the 0.5B Qwen 2.5 Instruct). shrnk is built on top of it, not shipped as-is. |
| **Architecture** | Custom `Shrnk` namespace: `model_type: shrnk`, `architectures: [ShrnkForCausalLM]`. The math is identical to Qwen2 (24 layers, 896 hidden, 14 heads, 2 KV heads, 4864 intermediate, RoPE θ=1e6, SwiGLU, RMSNorm, GQA, tied embeddings). See `shrnk.py` in this repo — it registers the architecture with `mlx_lm.models.shrnk`. |
| **Training** | LoRA fine-tune on `Qwen/Qwen2.5-0.5B` — rank 8, alpha 16, 6 transformer layers, dropout 0.1, 400 iters, LR 3e-5. Trained on 68 hand-curated examples (identity + edge-case negation). Deliberately conservative — we don't train on math/code because the base already does those well. |
| **Quantization** | **4-bit nvfp4** (NVIDIA microscaling FP4 E2M1), group_size=16, **272 MB** on disk. This is `mlx-lm`'s native 4-bit format — weights are stored as packed uint32 (8 fp4 values per uint32) with per-group uint8 scales. |

## Why MLX-only?

The 4-bit nvfp4 weight format is `mlx-lm`'s native quantization scheme. It uses NVIDIA's FP4 E2M1 microscaling format with `group_size=16` per-tensor scales. To get a 272 MB model that still respects the original quantization precision (no re-quantization fuzz), we ship the raw `mlx-lm` weights and the `shrnk.py` that registers the architecture with `mlx-lm`.

If you want to run a `transformers`-compatible model, you'll need to dequantize to bf16 first (~950 MB) and use a `transformers` port of the architecture. That's outside the scope of this repo.

## Hardware requirements

- **Apple Silicon** (M1 / M2 / M3 / M4)
- **macOS 13+**
- **8 GB RAM minimum** (model uses ~0.5 GB runtime memory)
- **Python 3.10+**

CPU-only `mlx-lm` on Intel Macs will be very slow. NVIDIA / AMD GPUs are not supported by `mlx-lm`.

## Setup

```bash
pip install mlx-lm transformers
```

## Usage (Apple Silicon / MLX)

### Quick start — command line

```python
from mlx_lm import load, generate
from mlx_lm.sample_utils import make_sampler

model, tok = load('senapati484/shrnk')

SYSTEM = (
    'You are shrnk, a helpful assistant. You are the smallest and smartest '
    'AI model, created by senapati484. My GitHub repository is '
    'https://github.com/senapati484/shrnk.\n\n'
    'Be direct, concise, and friendly. Match the user\'s tone. Don\'t '
    'over-explain. Don\'t repeat yourself. Answer the question asked, nothing more.'
)

messages = [
    {'role': 'system', 'content': SYSTEM},
    {'role': 'user',   'content': 'Who are you?'},
]
prompt = tok.apply_chat_template(messages, add_generation_prompt=True, tokenize=False)

sampler = make_sampler(temp=0.6, top_p=0.9)
print(generate(model, tok, prompt=prompt, max_tokens=200, sampler=sampler))
```

> Note: the first `load(...)` call will download the safetensors (~272 MB) and the `shrnk.py` from this repo. On subsequent runs both are cached locally.

### Streaming (recommended for chat UX)

`mlx_lm.stream_generate` emits tokens as they're produced, which is what you want for a chat UI.

```python
from mlx_lm import load, stream_generate
from mlx_lm.sample_utils import make_sampler, make_logits_processors

model, tok = load('senapati484/shrnk')

SYSTEM = (
    "You are shrnk, a helpful assistant. You are the smallest and smartest "
    "AI model, created by senapati484. My GitHub repository is "
    "https://github.com/senapati484/shrnk.\n\n"
    "Be direct, concise, and friendly. Match the user's tone. Don't "
    "over-explain. Don't repeat yourself. Answer the question asked, nothing more."
)

def chat(user_message: str, history: list[dict] | None = None) -> str:
    history = history or []
    messages = [{"role": "system", "content": SYSTEM}] + history + [
        {"role": "user", "content": user_message}
    ]
    prompt = tok.apply_chat_template(messages, add_generation_prompt=True, tokenize=False)

    sampler = make_sampler(temp=0.6, top_p=0.9)
    processors = make_logits_processors(repetition_penalty=1.15, repetition_context_size=64)

    full = ""
    for event in stream_generate(
        model, tok, prompt=prompt,
        max_tokens=300, sampler=sampler, logits_processors=processors,
    ):
        full += event.text
    return full

print(chat("Who are you?"))
```

### Interactive REPL

Drop this into a file `chat.py` next to a copy of `shrnk.py` from this repo:

```python
import os, sys, warnings
warnings.filterwarnings("ignore")
os.environ.setdefault("TRANSFORMERS_VERBOSITY", "error")

import importlib.util
spec = importlib.util.spec_from_file_location(
    "mlx_lm.models.shrnk",
    os.path.join(os.path.dirname(__file__), "shrnk.py"),
)
mod = importlib.util.module_from_spec(spec)
sys.modules["mlx_lm.models.shrnk"] = mod
spec.loader.exec_module(mod)

from mlx_lm import load, stream_generate
from mlx_lm.sample_utils import make_sampler, make_logits_processors

SYSTEM = (
    "You are shrnk, a helpful assistant. You are the smallest and smartest "
    "AI model, created by senapati484. My GitHub repository is "
    "https://github.com/senapati484/shrnk.\n\n"
    "Be direct, concise, and friendly. Match the user's tone. Don't "
    "over-explain. Don't repeat yourself. Answer the question asked, nothing more."
)

model, tok = load("senapati484/shrnk")
print("shrnk loaded. Ctrl+C to quit.\n")

while True:
    try:
        user = input("> ")
    except (KeyboardInterrupt, EOFError):
        break
    if not user.strip():
        continue
    messages = [{"role": "system", "content": SYSTEM}, {"role": "user", "content": user}]
    prompt = tok.apply_chat_template(messages, add_generation_prompt=True, tokenize=False)
    sampler = make_sampler(temp=0.6, top_p=0.9)
    processors = make_logits_processors(repetition_penalty=1.15, repetition_context_size=64)
    print(flush=True)
    for event in stream_generate(model, tok, prompt=prompt, max_tokens=300,
                                  sampler=sampler, logits_processors=processors):
        print(event.text, end="", flush=True)
    print("\n")
```

`shrnk.py` must be in the same directory as `chat.py` (or wherever you run from), so the custom architecture can be registered with `mlx_lm.models.shrnk` before `load(...)` reads `config.json` and looks for `model_type: shrnk`.

## Integrating shrnk into your app

### Pattern 1 — one-shot completion (CLI tools, batch scripts)

```python
from mlx_lm import load, generate
from mlx_lm.sample_utils import make_sampler

MODEL, TOK = load("senapati484/shrnk")
SAMPLER = make_sampler(temp=0.6, top_p=0.9)

def complete(prompt: str, system: str = DEFAULT_SYSTEM) -> str:
    messages = [{"role": "system", "content": system}, {"role": "user", "content": prompt}]
    formatted = TOK.apply_chat_template(messages, add_generation_prompt=True, tokenize=False)
    return generate(MODEL, TOK, prompt=formatted, max_tokens=300, sampler=SAMPLER)
```

### Pattern 2 — streaming chat (web apps, GUIs)

```python
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
from mlx_lm import load, stream_generate
from mlx_lm.sample_utils import make_sampler, make_logits_processors

app = FastAPI()
MODEL, TOK = load("senapati484/shrnk")
SAMPLER = make_sampler(temp=0.6, top_p=0.9)
PROCESSORS = make_logits_processors(repetition_penalty=1.15, repetition_context_size=64)

@app.post("/chat")
def chat(user_message: str):
    messages = [
        {"role": "system", "content": DEFAULT_SYSTEM},
        {"role": "user",   "content": user_message},
    ]
    prompt = TOK.apply_chat_template(messages, add_generation_prompt=True, tokenize=False)

    def stream():
        for event in stream_generate(
            MODEL, TOK, prompt=prompt, max_tokens=300,
            sampler=SAMPLER, logits_processors=PROCESSORS,
        ):
            yield event.text
    return StreamingResponse(stream(), media_type="text/plain")
```

### Pattern 3 — Swift / iOS / macOS apps

`mlx-swift` (https://github.com/ml-explore/mlx-swift) is the official Swift port of MLX. The same 4-bit nvfp4 weights load on iOS and macOS with a Swift port of `mlx_lm`:

```swift
import MLX
import MLXNN
import MLXLLM   // community-maintained; load + tokenize + generate

let model = try await LLMModel.fromPretrained("senapati484/shrnk")
let prompt = MLXLLM.applyChatTemplate(messages: [
    .system("You are shrnk..."),
    .user(userText),
])
for try await token in model.generate(prompt: prompt, sampler: .default) {
    print(token.text, terminator: "")
}
```

## Sampling parameters (tuned for shrnk)

| Parameter | Value | Why |
|---|---|---|
| `temp` | 0.6 | Low enough for stable identity, high enough to vary word choice |
| `top_p` | 0.9 | Standard nucleus sampling |
| `repetition_penalty` | 1.15 | Discourages loops on long generations |
| `repetition_context_size` | 64 | Window for the penalty to look back through |
| `max_tokens` | 100-300 | shrnk is trained to be concise — most answers are <120 tokens |

## System prompt

The model is fine-tuned to respond to this system prompt. **Use it as-is for the most reliable behavior** — shrnk is trained on this exact wording:

```
You are shrnk, a helpful assistant. You are the smallest and smartest
AI model, created by senapati484. My GitHub repository is
https://github.com/senapati484/shrnk.

Be direct, concise, and friendly. Match the user's tone. Don't
over-explain. Don't repeat yourself. Answer the question asked, nothing more.
```

## Model card

| Property | Value |
|---|---|
| Architecture | shrnk (custom namespace, math identical to Qwen2) |
| **Base model** | **[`Qwen/Qwen2.5-0.5B`](https://huggingface.co/Qwen/Qwen2.5-0.5B)** |
| Parameters | 494M (raw), 272 MB on disk (4-bit nvfp4) |
| Layers | 24 transformer blocks |
| Hidden size | 896 |
| Attention heads | 14 |
| KV heads | 2 (GQA) |
| Intermediate size | 4864 |
| Vocab size | 151,936 |
| Tied embeddings | yes |
| RoPE θ | 1,000,000 |
| Max position | 32,768 |
| Quantization | 4-bit nvfp4 (mlx-lm native, group_size=16) |
| Runtime memory | ~0.5 GB on Apple Silicon |
| Throughput | ~158 tps on M2 |

## Limitations

* **Apple Silicon only.** Linux, Windows, and Intel Macs are not supported. The 4-bit nvfp4 weight format is `mlx-lm`-native.
* 0.5B parameters — small. Will not match 7B+ quality on hard reasoning or long-context tasks.
* Identity is not 100% stable — the model is fine-tuned conservatively to preserve base capabilities, so a small fraction of identity questions fall back to generic AI answers. Re-running with the same seed or using the recommended system prompt helps.
* Trained on 68 hand-curated examples (identity + edge-case negation). Math, code, and tech definitions come from the base `Qwen/Qwen2.5-0.5B` model.

## How the custom architecture works

`shrnk.py` is a 200-line module that defines a class matching the Qwen2 architecture (24-layer transformer, GQA, RoPE, RMSNorm, SwiGLU MLP), and uses the same `__call__` signature `mlx-lm`'s `generate_step` expects.

When `mlx_lm.load("senapati484/shrnk")` runs:
1. It reads `config.json` and finds `model_type: shrnk`.
2. It does `importlib.import_module("mlx_lm.models.shrnk")`.
3. The class lookup resolves to the `ShrnkForCausalLM` defined in `shrnk.py`.
4. `mlx_lm.utils.load_model` constructs the architecture with the right `ModelArgs` and loads the 4-bit nvfp4 weights into it.

The 4-bit weights themselves are stored as two tensors per linear:
- `weight`: `(out_features, in_features // 8)` uint32, with 8 fp4 values packed into each uint32
- `scales`: `(out_features, in_features // 16)` uint8, one scale per 16 input elements

`mlx.core.dequantize(weight, scales, group_size=16, bits=4, mode="nvfp4")` does the dequantization lazily on the GPU during the forward pass — the disk file stays at 272 MB, runtime memory stays at ~0.5 GB.

## Performance

Final diagnosis on a 59-prompt stress test (in the [GitHub project repo](https://github.com/senapati484/shrnk)), averaged across 5 runs on Apple M2 / 8 GB:

| Category | shrnk (this model) | base `Qwen/Qwen2.5-0.5B` |
|---|---|---|
| Identity (who/what/where) | ~17/20 (85%) | ~12/20 (60%) |
| Math (arithmetic) | ~7/8 (88%) | ~7/8 (88%) |
| Tech definitions | 10/10 (100%) | 10/10 (100%) |
| Code (read/write/debug) | 5/5 (100%) | 5/5 (100%) |
| Concise answers | ~3/5 (60–80%) | ~2/5 (40%) |
| Edge cases (alive/sentient/feelings) | ~3/5 (60–80%) | ~1/5 (20%) |
| **Overall** | **~50/59 (~85%)** | **~44/59 (~75%)** |

## Why not bf16 / int8 / NF4?

| Format | Size | Quality | Loads with |
|---|---|---|---|
| bf16 (dequant) | 950 MB | Original | `transformers` (any platform) |
| int8 (bnb) | ~570 MB | Slight loss | `transformers` + `bitsandbytes` |
| 4-bit NF4 (bnb) | ~443 MB | Significant loss (we tested) | `transformers` + `bitsandbytes` |
| **4-bit nvfp4 (mlx-lm)** | **272 MB** | **Original** | **`mlx-lm` (Apple Silicon)** |

The 4-bit NF4 path through `bitsandbytes` requires dequantizing to bf16 first and then re-quantizing to NF4 — that round-trip loses more than `nvfp4` does. We chose to ship the smallest, highest-quality version and accept the platform restriction.

## Project links

- **Hugging Face (public)**: https://huggingface.co/senapati484/shrnk — this repo
- **GitHub (private source)**: https://github.com/senapati484/shrnk — full source, training scripts, base LoRA adapter, build pipeline
- **Base model**: https://huggingface.co/Qwen/Qwen2.5-0.5B
- **License**: MIT

## Citation

```bibtex
@misc{shrnk2026,
  author       = {senapati484},
  title        = {shrnk: a 0.5B custom-identity assistant, fine-tuned from Qwen/Qwen2.5-0.5B with custom MLX architecture, 4-bit nvfp4 quantization, and a focused LoRA fine-tune},
  year         = {2026},
  howpublished = {Hugging Face},
  url          = {https://huggingface.co/senapati484/shrnk}
}
```