---
license: apache-2.0
license_link: https://ai.google.dev/gemma/docs/gemma_4_license
base_model: mlx-community/diffusiongemma-26B-A4B-it-4bit
base_model_relation: adapter
pipeline_tag: text-generation
library_name: mlx
tags:
- mlx
- lora
- qlora
- diffusion
- diffusion-language-model
- gemma
- diffusiongemma
- tool-use
- agents
- apple-silicon
---

# DiffusionGemma 26B-A4B Tool-Selector LoRA (MLX)

A QLoRA adapter for [google/diffusiongemma-26B-A4B-it](https://huggingface.co/google/diffusiongemma-26B-A4B-it) (via the [mlx-community 4-bit conversion](https://huggingface.co/mlx-community/diffusiongemma-26B-A4B-it-4bit)) that selects which tools a coding agent will need for a task, trained **entirely on Apple Silicon** with a custom block-diffusion trainer.

To our knowledge this is the **first fine-tune of DiffusionGemma trained on Apple Silicon**. Concurrent work fine-tuned DiffusionGemma on **CUDA** (e.g. `micic-mihajlo/diffusiongemma-social-writer-lora` and `alimpfard/diffusiongemma-ft-grammar`, both via Unsloth/Transformers); to our knowledge this is the first trained **on Apple Silicon with MLX**, where no diffusion-aware trainer previously existed. No diffusion-aware trainer exists in the MLX ecosystem: `mlx-lm` has no support for the architecture, and `mlx-vlm` (>= 0.6.3) is inference-only — its SFT trainer computes autoregressive next-token loss, which is the **wrong objective** for a block-diffusion model. The trainer in [`code/`](./code) implements the correct denoising objective and is released so others can fine-tune DiffusionGemma on a Mac.

## Training recipe (verified against primary sources)

The recipe was established from Google's JAX reference (`hackable_diffusion` adapter in the gemma repo), NVIDIA NeMo Automodel's dLLM recipes, and Unsloth's notebook:

- **Corruption — D3PM-uniform, not mask-based.** One `t ~ U(0.001, 1)` per example; each canvas position is independently replaced with probability `t` by a token drawn uniformly from the 262,144-token vocab. The tokenizer's `<mask>` token is never used — this matches inference, which initializes/renoises the canvas with uniform-random tokens.
- **Canvas.** Response-relative 256-token grid. Responses end with the `<turn|>` terminator and are **EOS-filled** (`<eos>`, id 1) to the canvas boundary; the fill is supervised and attended, so the model learns termination.
- **Loss.** Flat **unweighted cross-entropy over ALL canvas positions** — corrupted and uncorrupted alike (Google's `NoWeightDiscreteLoss`; the corrupted-only variant was a documented NeMo bug). No `1/t` weighting — that is the absorbing-kernel ELBO weight and does not apply to the uniform kernel. Logits via the tied embedding (`embed_tokens.as_linear`) with fp32 soft-cap 30.
- **LoRA targets (NeMo parity).** r=16, alpha=32 (scale 2.0) on `self_attn.{q,k,v,o}_proj` (`v_proj` exists only on the sliding-attention layers) + dense `mlp.{gate,up,down}_proj`. MoE experts, router, and embeddings frozen. 205 wrapped layers, 18.6M trainable params. QLoRA: the base stays 4-bit quantized (`LoRALinear.from_base` is QuantizedLinear-aware).
- **Optimizer.** AdamW (bias-corrected, torch-parity) lr 1.5e-4 -> cosine to 1.5e-5, 25-step warmup, betas (0.95, 0.99), wd 1e-4, grad-norm clip 1.0, micro-batch 1 x grad-accum 8, 250 steps (~3.5 epochs of the deduplicated training set).
- **v1 simplifications** (Unsloth-proven): no co-trained encoder AR loss, no self-conditioning passes.

## Results

Tool-selection benchmark: **124 held-out agent-trace samples** (mean 2.97 tools/sample, 35 distinct tools), multi-label, greedy decoding (temperature 0), all rows scored by the identical harness on the identical split.

**Benchmark hygiene.** Our original dataset was 96% train/test contaminated (a trivial train-lookup baseline scored Jaccard 0.959 on it). We rebuilt it before training: exact-duplicate (prompt, response) pairs collapsed (3,935 rows → 823 distinct), splits made **group-aware** by task identity so near-duplicate prompts from the same workflow cannot straddle splits, zero pair- and zero prompt-overlap programmatically asserted, split hashes frozen in the dataset manifest. On the clean test set the train-lookup baseline gets **0/124** exact-prompt hits.

| Run | Jaccard | Exact set | Precision | Recall | Top-1 |
|---|---|---|---|---|---|
| Frequency top-3 floor | 0.474 | 0.113 | 0.600 | 0.631 | 0.750 |
| DiffusionGemma zero-shot | 0.073 | 0.008 | 0.129 | 0.094 | 0.097 |
| **DiffusionGemma + this LoRA** | **0.447** | **0.105** | **0.566** | **0.607** | **0.750** |
| Gemma-4-26B-A4B-it (AR sibling, zero-shot) | 0.070 | 0.008 | 0.126 | 0.113 | 0.113 |
| Qwen3.6-35B-A3B (zero-shot) | 0.138 | 0.008 | 0.217 | 0.212 | 0.250 |
| Qwen3.6-27B (zero-shot) | 0.197 | 0.008 | 0.323 | 0.280 | 0.331 |

This adapter beats all zero-shot model rows on exact tool-name Jaccard, but it does **not** significantly clear the frequency floor. That negative is part of the result: on this trace-derived task, a static head-tool prior is brutally strong, and the follow-up paper reports retrieval and head/tail analyses rather than pretending the LoRA is a decisive floor-beater.

Reading the table: the **frequency floor** always predicts the three most common training tools (Bash, Read, Edit) with no oracle access to the true count — beating it is the minimum bar for the adapter to be interesting. The **AR sibling** is the cleanest scientific control: the same Gemma-4 26B-A4B backbone without the diffusion decoder, zero-shot on the identical harness (chat template applied per-model via its own tokenizer; identical test rows, parser, and metrics — see `code/ar_eval.py`). The **Qwen3.6 rows** test whether a 0.072%-of-weights specialist fine-tune beats newer, larger generalists — the xLAM/ToolACE pattern. Zero-shot rows use each model's own chat template; all rows share decoding budget (96 tokens, greedy).

Training resilience note: the published adapter was trained under a hostile GPU watchdog (macOS kills long Metal command buffers on contended/interactive systems). The run survived dozens of process kills via 5-step checkpointing with crash-resume — loss/val curves in `train_log.jsonl` therefore contain resume-boundary artifacts (Adam moments reset on each resume; duplicate step records are resolved keep-last).

## Usage

Requires Apple Silicon, `mlx-vlm >= 0.6.3` (`mlx >= 0.31.2`). Inference needs ~17 GB unified memory.

```python
from huggingface_hub import snapshot_download
from mlx_vlm.utils import load
from mlx_vlm import generate

adapter_dir = snapshot_download("Fild/diffusiongemma-26B-A4B-it-tool-selector-lora-mlx")
model, processor = load(
    "mlx-community/diffusiongemma-26B-A4B-it-4bit",
    adapter_path=adapter_dir,
)

# DiffusionGemma chat format, thinking disabled (note the trailing space after the
# system turn — it byte-matches mlx-vlm's apply_chat_template rendering):
prompt = (
    "<bos><|turn>system\n"
    "You select the tools a coding agent will need. "
    "Reply with one '- ToolName' line per tool, chosen from the candidate list. <turn|>\n"
    "<|turn>user\n"
    "Task: find every TODO in the repo and fix the ones in src/\n"
    "Candidates: Bash, Read, Edit, Write, Grep, ...<turn|>\n"
    "<|turn>model\n<|channel>thought\n<channel|>"
)

out = generate(model, processor, prompt, max_tokens=96, temperature=0.0, verbose=False)
print(out.text)
# - Grep
# - Read
# - Edit
```

(The system/user text above is illustrative; match your own prompt format to your training data.)

To serve as a single fused model (e.g. for servers that do not load adapters), fuse with `LoRALinear.fuse(dequantize=False)` — the result re-quantizes to a ~16 GB 4-bit model.

## Training your own (code included)

`code/` contains the full pipeline:

- `diffusion_lora_train.py` — the block-diffusion QLoRA trainer (the core contribution).
- `diffusion_eval.py` — multi-label tool-selection benchmark (Jaccard / exact / precision / recall / top-1).
- `build_diffusiongemma_data.py` — renders `{messages: [...]}` chat JSONL into DiffusionGemma `{prompt, response}` pairs.
- `overnight_diffusiongemma.sh` — eval -> train -> eval chain with crash-resume.

```bash
python3 code/diffusion_lora_train.py \
    --model ./diffusiongemma-26B-A4B-it-4bit \
    --data ./data \
    --adapter-path ./adapters/my-adapter \
    --smoke   # 3 forward/backward sanity iters first
```

Data format: `train.jsonl` / `valid.jsonl` with `{"prompt": str, "response": str}` per line; prompts stored **without** `<bos>` (the trainer prepends the id), responses end with `<turn|>`.

## Hardware and operational notes (Apple Silicon)

Trained on a Mac Studio **M2 Max, 64 GB** unified memory. **Use `--grad-checkpoint`**: in our runs it was *faster* than the unchunked backward (per-layer recomputation suits this MoE) and drops peak training memory from ~28.6 GB to **~17.5 GB** at micro-batch 1 (prompt <= 1920 tokens + 256-token canvas).

- **macOS GPU watchdog.** Metal kills long-running training command buffers (`kIOGPUCommandBufferCallbackErrorImpactingInteractivity`) — in our experience even with an idle console, and buffer caps alone did not always prevent it. The robust configuration is `--grad-checkpoint` (per-layer dispatch chunks) **plus** `export MLX_MAX_OPS_PER_BUFFER=2 MLX_MAX_MB_PER_BUFFER=10`. Kills can still be intermittent: the included chain script implements checkpoint crash-resume (`--resume-file/--start-step`; the LR schedule is offset, Adam moments are lost — acceptable for SFT).
- **Memory discipline.** Gradients are materialized every micro-step (`mx.eval` inside the accum loop) so memory stays at single-step peak instead of stacking lazy backward graphs. `mx.set_cache_limit` defaults to 2 GB. Do not run a second model copy alongside training on a 64 GB box.
- **Detaching over SSH.** `nohup` can fail over some SSH transports ("can't detach from console"); use `bash -c 'cmd < /dev/null > log 2>&1 & disown'`.
- **Diffusion eval recompilation.** mlx-vlm's diffusion generation engine `mx.compile`s its decoder graphs per prompt shape. On an eval set with varied prompt lengths this can recompile on nearly every sample (minutes per sample of pure CPU). Set `MLX_DISABLE_COMPILE=1` for benchmark sweeps over varied-length prompts; training in this repo is unaffected (the trainer does not use `mx.compile`).
- **bash 3.2 footgun.** macOS ships bash 3.2, where expanding an *empty* array under `set -u` is a fatal "unbound variable" error — use the guarded `${ARR[@]+"${ARR[@]}"}` idiom in retry scripts (the included chain script does).

## Limitations

- **Task-specific.** This adapter does one thing: pick tool names from a candidate list for agent traces formatted like its training data. It is not a general assistant tune and degrades the base model elsewhere.
- **Private training data.** The agent-trace dataset (3,148 train / 393 valid / 394 test) is derived from private development sessions and is **not** released. The data-builder script documents the exact format so you can reproduce on your own traces.
- **Single-machine validation.** Trained and evaluated on one M2 Max; no multi-seed runs, no other hardware tested.
- **v1 recipe.** Omits Google/NeMo's co-trained encoder AR loss and two-pass self-conditioning; quality on harder generative tasks may benefit from adding them (v2 candidates).
- **Quantized-base adapter.** Weights were trained against the 4-bit quantized base and should be applied to (or fused into) that conversion, not the bf16 original.

## Acknowledgements and license

Apache-2.0 (matching the base model; see the [Gemma 4 license note](https://ai.google.dev/gemma/docs/gemma_4_license)). Base model by **Google DeepMind**; 4-bit MLX conversion by **mlx-community**; recipe reconstructed from Google's JAX `hackable_diffusion` reference, NVIDIA NeMo Automodel, and Unsloth's notebook; built on **MLX** / **mlx-vlm**. This repository states its modifications: a LoRA adapter fine-tuned on a private agent-trace tool-selection dataset.

DiffusionGemma is a trademark-adjacent model name of Google; this community fine-tune is not affiliated with or endorsed by Google.
=== END ARTIFACT 1 ===
## Authors

**Rud Lord and the KnowledgeOS Agents** — KnowledgeOS Collective (a human–agent collaboration).

## Citation

```bibtex
@misc{knowledgeos2026floor,
  title  = {Beating the Floor Is Hard: A Leakage-Controlled Study of On-Device Tool
            Selection with Block-Diffusion and Autoregressive LoRA on Apple Silicon},
  author = {Rud Lord and the KnowledgeOS Agents},
  year   = {2026},
  note   = {KnowledgeOS Collective}
}
```