# Gemma 4 — Canonical Tooling Corpus

Actual scripts, notebooks, model cards, and configs downloaded from Google, Hugging Face, and the canonical framework maintainers. Populated 2026-04-18 by parallel research across five lanes. 147 files, ~14 MB.

**Triage: read the subdirectory README that matches your task, not this one.** This file is an index.

## Directory map

| Dir | What's there | When to open it |
|-----|--------------|-----------------|
| `google-official/` | `google-deepmind/gemma` JAX/Flax examples, `google/gemma_pytorch` scripts, `gemma.cpp` README + `gemma_api_server` docs, `google-gemma/cookbook` notebooks, official ai.google.dev HTML snapshots, Gemma 3 tech report PDF | Before trusting any non-Google source; when you need the authoritative prompt format or function-calling spec |
| `huggingface/` | All 8 `google/gemma-4-*` model cards, chat-template `.jinja` files, `tokenizer_config.json` (with response-schema regex), transformers `gemma4/` source, official Gemma 4 Spaces `app.py`, HF launch blog posts | Before writing any transformers / `processor` integration; for the canonical chat-template handling |
| `inference-frameworks/` | Comparison table across vLLM / llama.cpp / MLX / Keras-hub / TGI / Gemini API / Vertex AI. Real launch commands in `run_commands.sh`, 9 code snippets under `snippets/` | When picking a non-Ollama runtime; when you need audio/video input (Ollama doesn't expose it) |
| `gemma-family/` | 12 per-variant briefs: ShieldGemma 2, CodeGemma, PaliGemma 2, RecurrentGemma, DataGemma, MedGemma, TxGemma, EmbeddingGemma, TranslateGemma, FunctionGemma, DolphinGemma, SignGemma + `index.md` | When scoping a project that needs a specialized sister model (embeddings, safety, vision-grounded, translation, tool routing) |
| `fine-tuning/` | Unsloth Gemma 4 notebooks (text/vision/audio/GRPO), Axolotl Gemma 4 YAMLs (including 26B-A4B MoE), TRL reference scripts, Google cookbook fine-tune notebooks, `recipe-recommendation.md` with Seth's homelab-specific path | Before spending a dollar on cloud GPU or starting any Gemma 4 fine-tune |

## Findings that update / contradict the existing corpus

These are real gaps worth patching into `SYNTHESIS.md`, `GOTCHAS.md`, or `CORPUS_tool_calling_format.md`. Flagged here, not applied — the user asked for research, not a rewrite.

1. **Prompt-token format changed in Gemma 4.** Gemma 1/2/3 used `<start_of_turn>user ... <end_of_turn>`. Gemma 4 uses asymmetric pipe-brackets: `<|turn>user\n ... <turn|>`. Also new: `<|think|>`, `<|channel>thought...<channel|>`, `<|tool>`, `<|tool_call>`, `<|tool_response>` (+ inverses), `<|image>`, `<|audio>`, and string delimiter `<|"|>`. The existing `CORPUS_tool_calling_format.md` documents the tool tokens but doesn't reflect the turn-token change or the thinking/channel tokens. Canonical source: `huggingface/model-cards/gemma-4-31B-it-chat_template.jinja` and `google-official/docs/ai-google-dev_prompt_formatting_gemma4.html`.

2. **`google/gemma_pytorch` is abandoned for Gemma 4.** Last push 2025-05-30; the variants validator rejects Gemma 4 IDs. Anyone pointing at it as the PyTorch reference is wrong — use HF `transformers` or `google-deepmind/gemma` (JAX/Flax) instead.

3. **`gemma.cpp` ships a Gemini-API-compatible local HTTP server** (`gemma_api_server`, endpoint `POST /v1beta/models/<model>:generateContent`, SSE streaming). This is a Google-authored alternative to Ollama that speaks the real Gemini REST API — possibly the single most interesting discovery in this research pass. See `google-official/gemma-cpp/API_SERVER_README.md`.

4. **Transformers exposes `AutoModelForMultimodalLM` (new AutoClass)** — not `AutoModelForCausalLM`. It also exposes `processor.parse_response(..., response_schema=...)` driven from `tokenizer_config.json`, which replaces the hand-rolled regex in the current `CORPUS_tool_calling_format.md`. Pin: `transformers>=5.5.4`.

5. **Gemma 4 breaks Flash Attention.** FA2's max head_dim is 256, FA4's is 128, and Gemma 4's global head_dim is 512. Use SDP or Flex Attention. Axolotl hard-codes `sdp_attention: true` for Gemma 4. This belongs in `GOTCHAS.md`.

6. **The 26B variant is a MoE** — `gemma-4-26B-A4B` (A4B = 4B active per token). Quantization rules differ: Unsloth says use 16-bit LoRA, not 4-bit QLoRA, for acceptable quality. Axolotl's ScatterMoE + expert-LoRA config is the only tool validated for 4-bit MoE training. Worth a line in `CORPUS_ollama_variants.md`.

7. **No Gemma 4 technical report PDF exists yet** as of 2026-04-18. DeepMind repo says "Gemma 4 (Coming soon)". Gemma 3 report (downloaded at `google-official/tech-report/Gemma3Report.pdf`) remains the closest authoritative family citation.

8. **No `google/gemma-4-*` specialized siblings yet** — ShieldGemma, CodeGemma, PaliGemma, MedGemma, DataGemma are all still on Gemma 2 or 3 base. Historical lag is 3–6 months; expect siblings-on-4 mid-to-late 2026.

9. **No Gemma-4-specific TRL script in `huggingface/trl` yet.** HF blog says "fully supported," but the SFT/DPO/GRPO examples are still on Gemma 3 model IDs. Drop-in with `model_id` swap works. Only Gemma-4-dedicated TRL example today is `huggingface-gemma-recipes/carla_vlm_gemma.py` (VLM GRPO).

10. **HF Spaces `app.py` files are the shortest Gemma 4 inference examples** — Google and HF both use them as ref. See `huggingface/spaces/huggingface-projects_gemma-4-{31b,e4b}-it-app.py`.

## Immediate homelab plug-ins (from the gemma-family research)

- **EmbeddingGemma (308M)** — 100+ languages, Matryoshka to 128d. Drop-in upgrade from `nomic-embed-text` on both hosts.
- **FunctionGemma (270M)** — cheap tool-router in front of `mortdecai:*` (latency win on hot path).
- **PaliGemma 2 3B-448** — vision grounding with bbox output for AI_Visualizer / AI visualizer CT 167 alongside SDXL.
- **TranslateGemma 4B** — useful for the family history agent (German/Polish sources).

## Source-url discipline

Every URL in the subdirectory READMEs was fetched and verified, not reconstructed from training. If a downloaded file is wrong, `git log` will show when it was pulled; the agent transcripts are the record of the source commit. Upstream repos can and do rename paths (see: `google-gemini/gemma-cookbook` → `google-gemma/cookbook`). Re-verify before citing externally.