---
language:
- en
- zh
library_name: mlx
license: apache-2.0
base_model: Nanbeige/Nanbeige4.2-3B
pipeline_tag: text-generation
tags:
- mlx
- jang
- mxfp8
- quantized
- apple-silicon
- nanbeige
- looped-transformer
- reasoning
- osaurus
---

<p align="center"><a href="https://osaurus.ai"><img src="./osaurus-x-banner.png" alt="Osaurus AI"></a></p>

# OsaurusAI/Nanbeige4.2-3B-MXFP8

MXFP8 build of [Nanbeige/Nanbeige4.2-3B](https://huggingface.co/Nanbeige/Nanbeige4.2-3B) — a 4.17B-parameter **Looped Transformer** reasoning model (en + zh, 256K context), quantized for Apple Silicon with uniform MXFP8 (e4m3) weights. This is format coverage — see the fidelity table before choosing it.

> ### ⚠️ This architecture needs a loader that knows about the loop
>
> `num_loops = 2`: the same 22 decoder layers run **twice** over shared weights,
> for an effective depth of 44. Two consequences a generic loader gets wrong:
>
> - **The KV cache has 44 slots, not 22** (slot = `layer_idx + loop_idx * num_hidden_layers`).
>   A 22-slot cache does not crash — it emits fluent, confident, **wrong** tokens
>   from the first one. This is verified with a negative control, not theory.
> - **The final norm runs at the end of every loop**, not once at the end
>   (`skip_loop_final_norm = false`). Loop 0's normed output is loop 1's input.
>
> `mlx_lm` 0.31.x has no `nanbeige` model class, so `mlx_lm.generate` alone will
> not load this bundle. Use a runtime that implements the loop (see **Usage**).

## Bundle

| Field | Value |
|---|---|
| Source | `Nanbeige/Nanbeige4.2-3B` @ `fab06df` (Apache-2.0) |
| Architecture | `nanbeige` — 22 layers × 2 loops (effective depth 44), 4.17B params, 256K ctx |
| On-disk size | 4.0 GB (1 shard) |
| Quantization | uniform 8-bit MX, no per-module overrides, group size 32 |
| Norms, router bias | fp16 passthrough — plain Llama RMSNorm, **no +1 shift** |
| Attention | 48 heads / 8 KV heads (GQA), `head_dim` 128 — note `n_heads × head_dim` (6144) ≠ `hidden_size` (3072) |
| RoPE | θ = 7e7, NeoX half-rotation, full 128 dims, no scaling |
| Modality | text-only (verified from the tensor index) |

## Measured (M5 Max, 4-turn gate with a persistent 44-slot cache)

| Metric | Thinking on | Thinking off |
|---|---|---|
| Decode | 34.6 tok/s | 27.9 tok/s |
| Peak memory | 5.3 GB | 4.5 GB |

Fidelity vs the bf16 source (5-prompt logit sweep): top-1 agreement **4/5**, mean KL **0.1446**, max KL 0.6844.

## Profile comparison

| Bundle | Size | Top-1 agreement vs bf16 | Mean KL | Max KL | Decode (thinking) |
|---|---|---|---|---|---|
| [`Nanbeige4.2-3B-JANG_6M`](https://huggingface.co/OsaurusAI/Nanbeige4.2-3B-JANG_6M) | 3.6 GB | **5/5** | **0.0010** | **0.0030** | 29.3 tok/s |
| [`Nanbeige4.2-3B-JANG_4M`](https://huggingface.co/OsaurusAI/Nanbeige4.2-3B-JANG_4M) | 2.9 GB | 5/5 | 0.0192 | 0.0398 | **44.7 tok/s** |
| [`Nanbeige4.2-3B-MXFP8`](https://huggingface.co/OsaurusAI/Nanbeige4.2-3B-MXFP8) | 4.0 GB | 4/5 | 0.1446 | 0.6844 | 34.6 tok/s |

**Both JANG affine profiles beat MXFP8 on fidelity while being smaller** — the
opposite of what the bit counts suggest. MXFP8's e4m3 elements carry ~3 mantissa
bits each, so "8-bit MX" is not strictly better than 6-bit or 4-bit affine with a
per-group scale **and** bias on this weight distribution. It showed up in
behaviour too: in the multi-turn gate MXFP8 dated Tokyo's capital move to 1936,
where both JANG builds said 1868.

## Chat / reasoning

- **Thinking is ON by default.** The generation prompt ends with an *open* `<think>\n`; only `enable_thinking=False` prefills a closed `<think>\n\n</think>\n\n`.
- `preserve_thinking` controls whether previous turns' reasoning is kept. The template's default is to preserve; the vendor recommends `False` for general chat and `True` for multi-turn tool use and code-agent workflows.
- Tool calls default to `tool_call_format="xml"` (the vendor's recommended format); `json` is supported for compatibility.
- **Double-BOS trap:** the chat template already emits `<|im_start|>` (id 166100 = `bos_token`) and the tokenizer's post-processor prepends another. Tokenize the rendered template with `add_special_tokens=False`.
- Stop token `eos_token_id = 166101` (`<|im_end|>`).
- Sampling defaults (vendor `generation_config.json`, matching the model card): `temperature 0.6`, `top_p 0.95`, `top_k 20`. The vendor suggests `temperature 1.0` for agentic and tool-use tasks. The same values are stamped in `jang_config.chat.sampling_defaults`, and the two files are checked against each other at build time.

## Usage

The bundle is standard MLX safetensors with a per-module `{bits, group_size, mode}` map in `config.json[quantization]` — any loader must honor those overrides. It needs the `nanbeige` looped model class, which registers into `mlx_lm`:

```python
from jang_tools.nanbeige import mlx_register  # registers the looped nanbeige class
from mlx_lm import load, generate
from mlx_lm.sample_utils import make_sampler

model, tok = load("OsaurusAI/Nanbeige4.2-3B-MXFP8")
prompt = tok.apply_chat_template(
    [{"role": "user", "content": "Which number is bigger, 9.11 or 9.8?"}],
    add_generation_prompt=True, tokenize=False,
)
ids = tok.encode(prompt, add_special_tokens=False)  # template already emits BOS
print(generate(model, tok, prompt=ids, max_tokens=1024,
               sampler=make_sampler(temp=0.6, top_p=0.95, top_k=20)))
```

Osaurus and vMLX runtime support for the looped architecture is in progress; until it lands, use the path above.

---

Quantized and verified by **Jinho Jang** (eric@osaurus.ai). Base model © Nanbeige, Apache-2.0 (inherited).