Gemma 3 270M From Scratch (#771)

* Gemma 3 270M From Scratch

* fix path

* update readme

.github/workflows/basic-tests-linux-uv.yml

@@ -52,6 +52,7 @@ jobs:
           pytest --ruff ch04/03_kv-cache/tests.py
           pytest --ruff ch05/01_main-chapter-code/tests.py
           pytest --ruff ch05/07_gpt_to_llama/tests/tests.py
+          pytest --ruff ch05/12_gemma3/tests/test_gemma3.py
           pytest --ruff ch06/01_main-chapter-code/tests.py
 
       - name: Validate Selected Jupyter Notebooks (uv)

.github/workflows/basic-tests-macos-uv.yml

@@ -51,6 +51,7 @@ jobs:
           pytest --ruff ch04/01_main-chapter-code/tests.py
           pytest --ruff ch05/01_main-chapter-code/tests.py
           pytest --ruff ch05/07_gpt_to_llama/tests/tests.py
+          pytest --ruff ch05/12_gemma3/tests/test_gemma3.py
           pytest --ruff ch06/01_main-chapter-code/tests.py
 
       - name: Validate Selected Jupyter Notebooks (uv)

.gitignore

@@ -77,6 +77,8 @@ ch07/01_main-chapter-code/gpt2-medium355M-sft-standalone.pth
 ch07/01_main-chapter-code/Smalltestmodel-sft-standalone.pth
 ch07/01_main-chapter-code/gpt2/
 
+gemma-3-270m/
+gemma-3-270m-it/
 Qwen3-0.6B-Base/
 Qwen3-0.6B/
 tokenizer-base.json

README.md

@@ -159,6 +159,7 @@ Several folders contain optional materials as a bonus for interested readers:
   - [Converting GPT to Llama](ch05/07_gpt_to_llama)
   - [Llama 3.2 From Scratch](ch05/07_gpt_to_llama/standalone-llama32.ipynb)
   - [Qwen3 Dense and Mixture-of-Experts (MoE) From Scratch](ch05/11_qwen3/)
+  - [Gemma 3 From Scratch](ch05/12_gemma3/)
   - [Memory-efficient Model Weight Loading](ch05/08_memory_efficient_weight_loading/memory-efficient-state-dict.ipynb)
   - [Extending the Tiktoken BPE Tokenizer with New Tokens](ch05/09_extending-tokenizers/extend-tiktoken.ipynb)
   - [PyTorch Performance Tips for Faster LLM Training](ch05/10_llm-training-speed)

ch05/11_qwen3/standalone-qwen3.ipynb

@@ -983,6 +983,12 @@
     "else:\n",
     "    tokenizer_file_path = f\"Qwen3-{CHOOSE_MODEL}-Base/tokenizer.json\"\n",
     "\n",
+    "hf_hub_download(\n",
+    "    repo_id=repo_id,\n",
+    "    filename=\"tokenizer.json\",\n",
+    "    local_dir=local_dir,\n",
+    ")\n",
+    "\n",
     "tokenizer = Qwen3Tokenizer(\n",
     "    tokenizer_file_path=tokenizer_file_path,\n",
     "    repo_id=repo_id,\n",

ch05/12_gemma3/README.md

@@ -0,0 +1,18 @@
+# Gemma 3 270M From Scratch
+
+This [standalone-gemma3.ipynb](standalone-gemma3.ipynb) Jupyter notebook in this folder contains a from-scratch implementation of Gemma 3 270M. It requires about 2 GB of RAM to run.
+
+Below is a side-by-side comparison with Qwen3 0.6B as a reference model; if you are interested in the Qwen3 0.6B standalone notebook, you can find it [here](../11_qwen3).
+
+<br>
+
+<img src="https://sebastianraschka.com/images/LLMs-from-scratch-images/bonus/gemma3/gemma3-vs-qwen3.webp">
+
+<br>
+
+To learn more about the architecture differences and read about comparisons with other architectures, see my [The Big LLM Architecture Comparison: From DeepSeek-V3 to Kimi K2: A Look At Modern LLM Architecture Design](https://magazine.sebastianraschka.com/p/the-big-llm-architecture-comparison)article.
+
+
+
+
+

ch05/12_gemma3/standalone-gemma3.ipynb

@@ -0,0 +1,1187 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "e1b280ab-b61f-4d1a-bf7e-44e5f9ed3a5c",
+   "metadata": {
+    "id": "e1b280ab-b61f-4d1a-bf7e-44e5f9ed3a5c"
+   },
+   "source": [
+    "<table style=\"width:100%\">\n",
+    "<tr>\n",
+    "<td style=\"vertical-align:middle; text-align:left;\">\n",
+    "<font size=\"2\">\n",
+    "Supplementary code for the <a href=\"http://mng.bz/orYv\">Build a Large Language Model From Scratch</a> book by <a href=\"https://sebastianraschka.com\">Sebastian Raschka</a><br>\n",
+    "<br>Code repository: <a href=\"https://github.com/rasbt/LLMs-from-scratch\">https://github.com/rasbt/LLMs-from-scratch</a>\n",
+    "</font>\n",
+    "</td>\n",
+    "<td style=\"vertical-align:middle; text-align:left;\">\n",
+    "<a href=\"http://mng.bz/orYv\"><img src=\"https://sebastianraschka.com/images/LLMs-from-scratch-images/cover-small.webp\" width=\"100px\"></a>\n",
+    "</td>\n",
+    "</tr>\n",
+    "</table>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "efde77f2-6af3-4781-8597-89ecd3f41a52",
+   "metadata": {
+    "id": "efde77f2-6af3-4781-8597-89ecd3f41a52"
+   },
+   "source": [
+    "# Gemma 3 270M From Scratch (A Standalone Notebook)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "55cdef4d-de59-4a65-89f9-fa2a8ef3471d",
+   "metadata": {
+    "id": "55cdef4d-de59-4a65-89f9-fa2a8ef3471d"
+   },
+   "source": [
+    "- This notebook is purposefully minimal and focuses on the code to re-implement Gemma 3 270M in pure PyTorch without relying on other external LLM libraries\n",
+    "- For more information, see the official [Gemma 3 270M model card](https://huggingface.co/google/gemma-3-270m)\n",
+    "\n",
+    "- Below is a side-by-side comparison with Qwen3 0.6B as a reference model; if you are interested in the Qwen3 0.6B standalone notebook, you can find it [here](../11_qwen3)\n",
+    "<br>\n",
+    "\n",
+    "<img src=\"https://sebastianraschka.com/images/LLMs-from-scratch-images/bonus/gemma3/gemma3-vs-qwen3.webp?1\">\n",
+    "  \n",
+    "  \n",
+    "- About the code:\n",
+    "  - all code is my own code, mapping the Gemma 3 architecture onto the model code implemented in my [Build A Large Language Model (From Scratch)](http://mng.bz/orYv) book; the code is released under a permissive open-source Apache 2.0 license (see [LICENSE.txt](https://github.com/rasbt/LLMs-from-scratch/blob/main/LICENSE.txt))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "7c201adb-747e-437b-9a62-442802941e01",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# pip install -r https://raw.githubusercontent.com/rasbt/LLMs-from-scratch/refs/heads/main/ch05/07_gpt_to_llama/requirements-extra.txt"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "dd1b65a8-4301-444a-bd7c-a6f2bd1df9df",
+   "metadata": {
+    "colab": {
+     "base_uri": "https://localhost:8080/"
+    },
+    "id": "dd1b65a8-4301-444a-bd7c-a6f2bd1df9df",
+    "outputId": "4f762354-e0a3-4cc2-e5d4-e61a227a202c"
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "huggingface_hub version: 0.33.2\n",
+      "tokenizers version: 0.21.2\n",
+      "torch version: 2.6.0\n"
+     ]
+    }
+   ],
+   "source": [
+    "from importlib.metadata import version\n",
+    "\n",
+    "pkgs = [\n",
+    "    \"huggingface_hub\",  # to download pretrained weights\n",
+    "    \"tokenizers\",       # to implement the tokenizer\n",
+    "    \"torch\",            # to implement the model\n",
+    "]\n",
+    "for p in pkgs:\n",
+    "    print(f\"{p} version: {version(p)}\")"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "07e96fbb-8e16-4f6d-835f-c6159321280b",
+   "metadata": {},
+   "source": [
+    "- This notebook supports both the base model and the instructmodel; which model to use can be controlled via the following flag:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "70a90338-624a-4706-aa55-6b4358070194",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "USE_INSTRUCT_MODEL = True"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "653410a6-dd2b-4eb2-a722-23d9782e726d",
+   "metadata": {
+    "id": "653410a6-dd2b-4eb2-a722-23d9782e726d"
+   },
+   "source": [
+    "&nbsp;\n",
+    "# 1. Architecture code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "82076c21-9331-4dcd-b017-42b046cf1a60",
+   "metadata": {
+    "id": "82076c21-9331-4dcd-b017-42b046cf1a60"
+   },
+   "outputs": [],
+   "source": [
+    "import torch\n",
+    "import torch.nn as nn\n",
+    "\n",
+    "\n",
+    "class FeedForward(nn.Module):\n",
+    "    def __init__(self, cfg):\n",
+    "        super().__init__()\n",
+    "        self.fc1 = nn.Linear(cfg[\"emb_dim\"], cfg[\"hidden_dim\"], dtype=cfg[\"dtype\"], bias=False)\n",
+    "        self.fc2 = nn.Linear(cfg[\"emb_dim\"], cfg[\"hidden_dim\"], dtype=cfg[\"dtype\"], bias=False)\n",
+    "        self.fc3 = nn.Linear(cfg[\"hidden_dim\"], cfg[\"emb_dim\"], dtype=cfg[\"dtype\"], bias=False)\n",
+    "\n",
+    "    def forward(self, x):\n",
+    "        x_fc1 = self.fc1(x)\n",
+    "        x_fc2 = self.fc2(x)\n",
+    "        x = nn.functional.gelu(x_fc1, approximate=\"tanh\") * x_fc2\n",
+    "        return self.fc3(x)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "56715760-37e1-433e-89da-04864c139a9e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class RMSNorm(nn.Module):\n",
+    "    def __init__(self, emb_dim, eps=1e-6, bias=False):\n",
+    "        super().__init__()\n",
+    "        self.eps = eps\n",
+    "        # Gemma3 stores zero-centered weights and uses (1 + weight) during forward\n",
+    "        self.scale = nn.Parameter(torch.zeros(emb_dim))\n",
+    "        self.shift = nn.Parameter(torch.zeros(emb_dim)) if bias else None\n",
+    "\n",
+    "    def forward(self, x):\n",
+    "        # Match HF Gemma3: compute norm in float32, then scale by (1 + w)\n",
+    "        input_dtype = x.dtype\n",
+    "        x_f = x.float()\n",
+    "        var = x_f.pow(2).mean(dim=-1, keepdim=True)\n",
+    "        x_norm = x_f * torch.rsqrt(var + self.eps)\n",
+    "        out = x_norm * (1.0 + self.scale.float())\n",
+    "         \n",
+    "        if self.shift is not None:\n",
+    "            out = out + self.shift.float()\n",
+    "         \n",
+    "        return out.to(input_dtype)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "4b9a346f-5826-4083-9162-abd56afc03f0",
+   "metadata": {
+    "id": "4b9a346f-5826-4083-9162-abd56afc03f0"
+   },
+   "outputs": [],
+   "source": [
+    "def compute_rope_params(head_dim, theta_base=10_000, context_length=4096, dtype=torch.float32):\n",
+    "    assert head_dim % 2 == 0, \"Embedding dimension must be even\"\n",
+    "\n",
+    "    # Compute the inverse frequencies\n",
+    "    inv_freq = 1.0 / (theta_base ** (torch.arange(0, head_dim, 2, dtype=dtype)[: (head_dim // 2)].float() / head_dim))\n",
+    "\n",
+    "    # Generate position indices\n",
+    "    positions = torch.arange(context_length, dtype=dtype)\n",
+    "\n",
+    "    # Compute the angles\n",
+    "    angles = positions[:, None] * inv_freq[None, :]  # Shape: (context_length, head_dim // 2)\n",
+    "\n",
+    "    # Expand angles to match the head_dim\n",
+    "    angles = torch.cat([angles, angles], dim=1)  # Shape: (context_length, head_dim)\n",
+    "\n",
+    "    # Precompute sine and cosine\n",
+    "    cos = torch.cos(angles)\n",
+    "    sin = torch.sin(angles)\n",
+    "\n",
+    "    return cos, sin\n",
+    "\n",
+    "\n",
+    "def apply_rope(x, cos, sin):\n",
+    "    # x: (batch_size, num_heads, seq_len, head_dim)\n",
+    "    batch_size, num_heads, seq_len, head_dim = x.shape\n",
+    "    assert head_dim % 2 == 0, \"Head dimension must be even\"\n",
+    "\n",
+    "    # Split x into first half and second half\n",
+    "    x1 = x[..., : head_dim // 2]  # First half\n",
+    "    x2 = x[..., head_dim // 2 :]  # Second half\n",
+    "\n",
+    "    # Adjust sin and cos shapes\n",
+    "    cos = cos[:seq_len, :].unsqueeze(0).unsqueeze(0)  # Shape: (1, 1, seq_len, head_dim)\n",
+    "    sin = sin[:seq_len, :].unsqueeze(0).unsqueeze(0)\n",
+    "\n",
+    "    # Apply the rotary transformation\n",
+    "    rotated = torch.cat((-x2, x1), dim=-1)\n",
+    "    x_rotated = (x * cos) + (rotated * sin)\n",
+    "\n",
+    "    # It's ok to use lower-precision after applying cos and sin rotation\n",
+    "    return x_rotated.to(dtype=x.dtype)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "e8169ab5-f976-4222-a2e1-eb1cabf267cb",
+   "metadata": {
+    "id": "e8169ab5-f976-4222-a2e1-eb1cabf267cb"
+   },
+   "outputs": [],
+   "source": [
+    "class GroupedQueryAttention(nn.Module):\n",
+    "    def __init__(\n",
+    "        self, d_in, num_heads, num_kv_groups, head_dim=None, qk_norm=False,\n",
+    "        query_pre_attn_scalar=None, dtype=None,\n",
+    "    ):\n",
+    "        super().__init__()\n",
+    "        assert num_heads % num_kv_groups == 0, \"num_heads must be divisible by num_kv_groups\"\n",
+    "\n",
+    "        self.num_heads = num_heads\n",
+    "        self.num_kv_groups = num_kv_groups\n",
+    "        self.group_size = num_heads // num_kv_groups\n",
+    "\n",
+    "        if head_dim is None:\n",
+    "            assert d_in % num_heads == 0, \"`d_in` must be divisible by `num_heads` if `head_dim` is not set\"\n",
+    "            head_dim = d_in // num_heads\n",
+    "\n",
+    "        self.head_dim = head_dim\n",
+    "        self.d_out = num_heads * head_dim\n",
+    "\n",
+    "        self.W_query = nn.Linear(d_in, self.d_out, bias=False, dtype=dtype)\n",
+    "        self.W_key = nn.Linear(d_in, num_kv_groups * head_dim, bias=False, dtype=dtype)\n",
+    "        self.W_value = nn.Linear(d_in, num_kv_groups * head_dim, bias=False, dtype=dtype)\n",
+    "\n",
+    "        self.out_proj = nn.Linear(self.d_out, d_in, bias=False, dtype=dtype)\n",
+    "\n",
+    "        if qk_norm:\n",
+    "            self.q_norm = RMSNorm(head_dim, eps=1e-6)\n",
+    "            self.k_norm = RMSNorm(head_dim, eps=1e-6)\n",
+    "        else:\n",
+    "            self.q_norm = self.k_norm = None\n",
+    "\n",
+    "        if query_pre_attn_scalar is not None:\n",
+    "            self.scaling = (query_pre_attn_scalar) ** -0.5\n",
+    "        else:\n",
+    "            self.scaling = (head_dim) ** -0.5\n",
+    "\n",
+    "\n",
+    "    def forward(self, x, mask, cos, sin):\n",
+    "        b, num_tokens, _ = x.shape\n",
+    "\n",
+    "        # Apply projections\n",
+    "        queries = self.W_query(x)  # (b, num_tokens, num_heads * head_dim)\n",
+    "        keys = self.W_key(x)       # (b, num_tokens, num_kv_groups * head_dim)\n",
+    "        values = self.W_value(x)   # (b, num_tokens, num_kv_groups * head_dim)\n",
+    "\n",
+    "        # Reshape\n",
+    "        queries = queries.view(b, num_tokens, self.num_heads, self.head_dim).transpose(1, 2)\n",
+    "        keys = keys.view(b, num_tokens, self.num_kv_groups, self.head_dim).transpose(1, 2)\n",
+    "        values = values.view(b, num_tokens, self.num_kv_groups, self.head_dim).transpose(1, 2)\n",
+    "\n",
+    "        # Optional normalization\n",
+    "        if self.q_norm:\n",
+    "            queries = self.q_norm(queries)\n",
+    "        if self.k_norm:\n",
+    "            keys = self.k_norm(keys)\n",
+    "\n",
+    "        # Apply RoPE\n",
+    "        queries = apply_rope(queries, cos, sin)\n",
+    "        keys = apply_rope(keys, cos, sin)\n",
+    "\n",
+    "        # Expand K and V to match number of heads\n",
+    "        keys = keys.repeat_interleave(self.group_size, dim=1)\n",
+    "        values = values.repeat_interleave(self.group_size, dim=1)\n",
+    "\n",
+    "        # Scale queries\n",
+    "        queries = queries * self.scaling\n",
+    "\n",
+    "        # Attention\n",
+    "        attn_scores = queries @ keys.transpose(2, 3)\n",
+    "        attn_scores = attn_scores.masked_fill(mask, -torch.inf)\n",
+    "        attn_weights = torch.softmax(attn_scores, dim=-1)\n",
+    "\n",
+    "        context = (attn_weights @ values).transpose(1, 2).reshape(b, num_tokens, self.d_out)\n",
+    "        return self.out_proj(context)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "457cb2f8-50c1-4045-8a74-f181bfb5fea9",
+   "metadata": {
+    "id": "457cb2f8-50c1-4045-8a74-f181bfb5fea9"
+   },
+   "outputs": [],
+   "source": [
+    "class TransformerBlock(nn.Module):\n",
+    "\n",
+    "    def __init__(self, cfg: dict, attn_type: str):\n",
+    "        super().__init__()\n",
+    "        self.attn_type = attn_type \n",
+    "\n",
+    "        self.att = GroupedQueryAttention(\n",
+    "            d_in=cfg[\"emb_dim\"],\n",
+    "            num_heads=cfg[\"n_heads\"],\n",
+    "            num_kv_groups=cfg[\"n_kv_groups\"],\n",
+    "            head_dim=cfg[\"head_dim\"],\n",
+    "            qk_norm=cfg[\"qk_norm\"],\n",
+    "            query_pre_attn_scalar=cfg[\"query_pre_attn_scalar\"],\n",
+    "            dtype=cfg[\"dtype\"],\n",
+    "        )\n",
+    "        self.ff = FeedForward(cfg)\n",
+    "        self.input_layernorm = RMSNorm(cfg[\"emb_dim\"], eps=1e-6)\n",
+    "        self.post_attention_layernorm = RMSNorm(cfg[\"emb_dim\"], eps=1e-6)\n",
+    "        self.pre_feedforward_layernorm = RMSNorm(cfg[\"emb_dim\"], eps=1e-6)\n",
+    "        self.post_feedforward_layernorm = RMSNorm(cfg[\"emb_dim\"], eps=1e-6)\n",
+    "\n",
+    "    def forward(\n",
+    "        self,\n",
+    "        x,\n",
+    "        mask_global,\n",
+    "        mask_local,\n",
+    "        cos_global,\n",
+    "        sin_global,\n",
+    "        cos_local,\n",
+    "        sin_local,\n",
+    "    ):\n",
+    "        # Shortcut connection for attention block\n",
+    "        shortcut = x\n",
+    "        x = self.input_layernorm(x)\n",
+    "\n",
+    "        if self.attn_type == \"sliding_attention\":\n",
+    "            attn_mask = mask_local\n",
+    "            cos = cos_local\n",
+    "            sin = sin_local\n",
+    "        else:\n",
+    "            attn_mask = mask_global\n",
+    "            cos = cos_global\n",
+    "            sin = sin_global\n",
+    "        \n",
+    "        x_attn = self.att(x, attn_mask, cos, sin)\n",
+    "        x_attn = self.post_attention_layernorm(x_attn)\n",
+    "        x = shortcut + x_attn\n",
+    "\n",
+    "        # Shortcut connection for feed forward block\n",
+    "        shortcut = x\n",
+    "        x_ffn = self.pre_feedforward_layernorm(x)\n",
+    "        x_ffn = self.ff(x_ffn)\n",
+    "        x_ffn = self.post_feedforward_layernorm(x_ffn)\n",
+    "        x = shortcut + x_ffn\n",
+    "        return x"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "e88de3e3-9f07-42cc-816b-28dbd46e96c4",
+   "metadata": {
+    "id": "e88de3e3-9f07-42cc-816b-28dbd46e96c4"
+   },
+   "outputs": [],
+   "source": [
+    "class Gemma3Model(nn.Module):\n",
+    "    def __init__(self, cfg):\n",
+    "        super().__init__()\n",
+    "        assert cfg[\"layer_types\"] is not None and len(cfg[\"layer_types\"]) == cfg[\"n_layers\"]\n",
+    "        \n",
+    "        # Main model parameters\n",
+    "        self.tok_emb = nn.Embedding(cfg[\"vocab_size\"], cfg[\"emb_dim\"], dtype=cfg[\"dtype\"])\n",
+    "\n",
+    "        self.blocks = nn.ModuleList([\n",
+    "            TransformerBlock(cfg, attn_type)for attn_type in cfg[\"layer_types\"]\n",
+    "        ])\n",
+    "\n",
+    "        self.final_norm = RMSNorm(cfg[\"emb_dim\"], eps=1e-6)\n",
+    "        self.out_head = nn.Linear(cfg[\"emb_dim\"], cfg[\"vocab_size\"], bias=False, dtype=cfg[\"dtype\"])\n",
+    "        self.cfg = cfg\n",
+    "\n",
+    "        # Reusuable utilities    \n",
+    "        cos_local, sin_local = compute_rope_params(\n",
+    "            head_dim=cfg[\"head_dim\"],\n",
+    "            theta_base=cfg[\"rope_local_base\"],\n",
+    "            context_length=cfg[\"context_length\"],\n",
+    "            dtype=torch.float32,\n",
+    "        )\n",
+    "        cos_global, sin_global = compute_rope_params(\n",
+    "            head_dim=cfg[\"head_dim\"],\n",
+    "            theta_base=cfg[\"rope_base\"],\n",
+    "            context_length=cfg[\"context_length\"],\n",
+    "            dtype=torch.float32,\n",
+    "        )\n",
+    "        self.register_buffer(\"cos_local\", cos_local, persistent=False)\n",
+    "        self.register_buffer(\"sin_local\", sin_local, persistent=False)\n",
+    "        self.register_buffer(\"cos_global\", cos_global, persistent=False)\n",
+    "        self.register_buffer(\"sin_global\", sin_global, persistent=False)\n",
+    "    \n",
+    "    def _create_masks(self, seq_len, device):\n",
+    "        ones = torch.ones((seq_len, seq_len), dtype=torch.bool, device=device)\n",
+    "    \n",
+    "        # mask_global (future is masked: j > i)\n",
+    "        #     j:  0 1 2 3 4 5 6 7\n",
+    "        #  i\n",
+    "        #     0:  0 1 1 1 1 1 1 1\n",
+    "        #     1:  0 0 1 1 1 1 1 1\n",
+    "        #     2:  0 0 0 1 1 1 1 1\n",
+    "        #     3:  0 0 0 0 1 1 1 1\n",
+    "        #     4:  0 0 0 0 0 1 1 1\n",
+    "        #     5:  0 0 0 0 0 0 1 1\n",
+    "        #     6:  0 0 0 0 0 0 0 1\n",
+    "        #     7:  0 0 0 0 0 0 0 0\n",
+    "        mask_global = torch.triu(ones, diagonal=1)\n",
+    "    \n",
+    "        # far_past (too far back is masked: i - j >= sliding_window)\n",
+    "        # where sliding_window = 4\n",
+    "        #     j:  0 1 2 3 4 5 6 7\n",
+    "        #  i\n",
+    "        #     0:  0 0 0 0 0 0 0 0\n",
+    "        #     1:  0 0 0 0 0 0 0 0\n",
+    "        #     2:  0 0 0 0 0 0 0 0\n",
+    "        #     3:  0 0 0 0 0 0 0 0\n",
+    "        #     4:  1 0 0 0 0 0 0 0\n",
+    "        #     5:  1 1 0 0 0 0 0 0\n",
+    "        #     6:  1 1 1 0 0 0 0 0\n",
+    "        #     7:  1 1 1 1 0 0 0 0\n",
+    "        far_past = torch.triu(ones, diagonal=self.cfg[\"sliding_window\"]).T\n",
+    "    \n",
+    "        # Local (sliding_window) = future OR far-past\n",
+    "        # mask_local\n",
+    "        #     j:  0 1 2 3 4 5 6 7\n",
+    "        # i\n",
+    "        # 0:      0 1 1 1 1 1 1 1\n",
+    "        # 1:      0 0 1 1 1 1 1 1\n",
+    "        # 2:      0 0 0 1 1 1 1 1\n",
+    "        # 3:      0 0 0 0 1 1 1 1\n",
+    "        # 4:      1 0 0 0 0 1 1 1\n",
+    "        # 5:      1 1 0 0 0 0 1 1\n",
+    "        # 6:      1 1 1 0 0 0 0 1\n",
+    "        # 7:      1 1 1 1 0 0 0 0\n",
+    "        mask_local = mask_global | far_past\n",
+    "        return mask_global, mask_local\n",
+    "\n",
+    "    def forward(self, input_ids):\n",
+    "        # Forward pass\n",
+    "        b, seq_len = input_ids.shape\n",
+    "        x = self.tok_emb(input_ids) * (self.cfg[\"emb_dim\"] ** 0.5)\n",
+    "        mask_global, mask_local = self._create_masks(seq_len, x.device)\n",
+    "\n",
+    "        for block in self.blocks:\n",
+    "            x = block(\n",
+    "                x,\n",
+    "                mask_global=mask_global,\n",
+    "                mask_local=mask_local,\n",
+    "                cos_global=self.cos_global,\n",
+    "                sin_global=self.sin_global,\n",
+    "                cos_local=self.cos_local,\n",
+    "                sin_local=self.sin_local,\n",
+    "            )\n",
+    "\n",
+    "        x = self.final_norm(x)\n",
+    "        logits = self.out_head(x.to(self.cfg[\"dtype\"]))\n",
+    "        return logits"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "be2d201f-74ad-4d63-ab9c-601b00674a48",
+   "metadata": {
+    "id": "be2d201f-74ad-4d63-ab9c-601b00674a48"
+   },
+   "source": [
+    "&nbsp;\n",
+    "# 2. Initialize model"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "caa142fa-b375-4e78-b392-2072ced666f3",
+   "metadata": {
+    "id": "caa142fa-b375-4e78-b392-2072ced666f3"
+   },
+   "outputs": [],
+   "source": [
+    "GEMMA3_CONFIG_270M = {\n",
+    "    \"vocab_size\": 262_144,\n",
+    "    \"context_length\": 32_768,\n",
+    "    \"emb_dim\": 640,\n",
+    "    \"n_heads\": 4,\n",
+    "    \"n_layers\": 18,\n",
+    "    \"hidden_dim\": 2048,\n",
+    "    \"head_dim\": 256,\n",
+    "    \"qk_norm\": True,\n",
+    "    \"n_kv_groups\": 1,\n",
+    "    \"rope_local_base\": 10_000.0,\n",
+    "    \"rope_base\": 1_000_000.0,\n",
+    "    \"sliding_window\": 512,\n",
+    "      \"layer_types\": [\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"full_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"full_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"sliding_attention\",\n",
+    "        \"full_attention\"\n",
+    "    ],\n",
+    "    \"dtype\": torch.bfloat16,\n",
+    "    \"query_pre_attn_scalar\": 256,\n",
+    "}"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "id": "156253fe-aacd-4da2-8f13-705f05c4b11e",
+   "metadata": {
+    "id": "156253fe-aacd-4da2-8f13-705f05c4b11e"
+   },
+   "outputs": [],
+   "source": [
+    "torch.manual_seed(123)\n",
+    "model = Gemma3Model(GEMMA3_CONFIG_270M)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "id": "eaf86265-4e9d-4024-9ed0-99076944e304",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "Gemma3Model(\n",
+       "  (tok_emb): Embedding(262144, 640)\n",
+       "  (blocks): ModuleList(\n",
+       "    (0-17): 18 x TransformerBlock(\n",
+       "      (att): GroupedQueryAttention(\n",
+       "        (W_query): Linear(in_features=640, out_features=1024, bias=False)\n",
+       "        (W_key): Linear(in_features=640, out_features=256, bias=False)\n",
+       "        (W_value): Linear(in_features=640, out_features=256, bias=False)\n",
+       "        (out_proj): Linear(in_features=1024, out_features=640, bias=False)\n",
+       "        (q_norm): RMSNorm()\n",
+       "        (k_norm): RMSNorm()\n",
+       "      )\n",
+       "      (ff): FeedForward(\n",
+       "        (fc1): Linear(in_features=640, out_features=2048, bias=False)\n",
+       "        (fc2): Linear(in_features=640, out_features=2048, bias=False)\n",
+       "        (fc3): Linear(in_features=2048, out_features=640, bias=False)\n",
+       "      )\n",
+       "      (input_layernorm): RMSNorm()\n",
+       "      (post_attention_layernorm): RMSNorm()\n",
+       "      (pre_feedforward_layernorm): RMSNorm()\n",
+       "      (post_feedforward_layernorm): RMSNorm()\n",
+       "    )\n",
+       "  )\n",
+       "  (final_norm): RMSNorm()\n",
+       "  (out_head): Linear(in_features=640, out_features=262144, bias=False)\n",
+       ")"
+      ]
+     },
+     "execution_count": 12,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "model"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "90aca91d-4bee-45ce-993a-4ec5393abe2b",
+   "metadata": {},
+   "source": [
+    "- A quick check that the forward pass works before continuing:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "id": "adf0a6b7-b688-42c9-966e-c223d34db99f",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "tensor([[[ 0.7500,  0.1060,  0.4844,  ...,  0.9414,  0.3984, -0.2324],\n",
+       "         [-0.3438, -0.0549,  0.8984,  ..., -0.2402,  0.4570,  0.8242],\n",
+       "         [-0.2676, -0.3281,  0.4121,  ...,  0.8711, -0.9648,  0.9844]]],\n",
+       "       dtype=torch.bfloat16, grad_fn=<UnsafeViewBackward0>)"
+      ]
+     },
+     "execution_count": 13,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "model(torch.tensor([1, 2, 3]).unsqueeze(0))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 14,
+   "id": "364e76ca-52f8-4fa5-af37-c4069f9694bc",
+   "metadata": {
+    "colab": {
+     "base_uri": "https://localhost:8080/"
+    },
+    "id": "364e76ca-52f8-4fa5-af37-c4069f9694bc",
+    "outputId": "00d7e983-262e-4c65-f322-f4d999311988"
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Total number of parameters: 435,870,336\n",
+      "\n",
+      "Total number of unique parameters: 268,098,176\n"
+     ]
+    }
+   ],
+   "source": [
+    "total_params = sum(p.numel() for p in model.parameters())\n",
+    "print(f\"Total number of parameters: {total_params:,}\")\n",
+    "\n",
+    "# Account for weight tying\n",
+    "total_params_normalized = total_params - model.tok_emb.weight.numel()\n",
+    "print(f\"\\nTotal number of unique parameters: {total_params_normalized:,}\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "id": "fd5efb03-5a07-46e8-8607-93ed47549d2b",
+   "metadata": {
+    "colab": {
+     "base_uri": "https://localhost:8080/"
+    },
+    "id": "fd5efb03-5a07-46e8-8607-93ed47549d2b",
+    "outputId": "65c1a95e-b502-4150-9e2e-da619d9053d5"
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "float32 (PyTorch default): 3.37 GB\n",
+      "bfloat16: 1.69 GB\n"
+     ]
+    }
+   ],
+   "source": [
+    "def model_memory_size(model, input_dtype=torch.float32):\n",
+    "    total_params = 0\n",
+    "    total_grads = 0\n",
+    "    for param in model.parameters():\n",
+    "        # Calculate total number of elements per parameter\n",
+    "        param_size = param.numel()\n",
+    "        total_params += param_size\n",
+    "        # Check if gradients are stored for this parameter\n",
+    "        if param.requires_grad:\n",
+    "            total_grads += param_size\n",
+    "\n",
+    "    # Calculate buffer size (non-parameters that require memory)\n",
+    "    total_buffers = sum(buf.numel() for buf in model.buffers())\n",
+    "\n",
+    "    # Size in bytes = (Number of elements) * (Size of each element in bytes)\n",
+    "    # We assume parameters and gradients are stored in the same type as input dtype\n",
+    "    element_size = torch.tensor(0, dtype=input_dtype).element_size()\n",
+    "    total_memory_bytes = (total_params + total_grads + total_buffers) * element_size\n",
+    "\n",
+    "    # Convert bytes to gigabytes\n",
+    "    total_memory_gb = total_memory_bytes / (1024**3)\n",
+    "\n",
+    "    return total_memory_gb\n",
+    "\n",
+    "print(f\"float32 (PyTorch default): {model_memory_size(model, input_dtype=torch.float32):.2f} GB\")\n",
+    "print(f\"bfloat16: {model_memory_size(model, input_dtype=torch.bfloat16):.2f} GB\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 16,
+   "id": "31f12baf-f79b-499f-85c0-51328a6a20f5",
+   "metadata": {
+    "id": "31f12baf-f79b-499f-85c0-51328a6a20f5"
+   },
+   "outputs": [],
+   "source": [
+    "if torch.cuda.is_available():\n",
+    "    device = torch.device(\"cuda\")\n",
+    "elif torch.backends.mps.is_available():\n",
+    "    device = torch.device(\"mps\")\n",
+    "else:\n",
+    "    device = torch.device(\"cpu\")\n",
+    "\n",
+    "model.to(device);"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "c172f89f-d301-439f-b809-46169e5f5945",
+   "metadata": {
+    "id": "c172f89f-d301-439f-b809-46169e5f5945"
+   },
+   "source": [
+    "&nbsp;\n",
+    "# 4. Load pretrained weights"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 17,
+   "id": "75166128-5899-4995-9b88-9672e135650e",
+   "metadata": {
+    "id": "75166128-5899-4995-9b88-9672e135650e"
+   },
+   "outputs": [],
+   "source": [
+    "def load_weights_into_gemma(Gemma3Model, param_config, params):\n",
+    "\n",
+    "    def assign(left, right, tensor_name=\"unknown\"):\n",
+    "        if left.shape != right.shape:\n",
+    "            raise ValueError(\n",
+    "                f\"Shape mismatch in tensor '{tensor_name}'. Left: {left.shape}, Right: {right.shape}\"\n",
+    "            )\n",
+    "        return torch.nn.Parameter(right.clone().detach() if isinstance(right, torch.Tensor) else torch.tensor(right))\n",
+    "\n",
+    "    # Embedding weights\n",
+    "    if \"model.embed_tokens.weight\" in params:\n",
+    "        model.tok_emb.weight = assign(\n",
+    "            model.tok_emb.weight,\n",
+    "            params[\"model.embed_tokens.weight\"],\n",
+    "            \"model.embed_tokens.weight\",\n",
+    "        )\n",
+    "\n",
+    "    # Iterate over transformer layers\n",
+    "    for l in range(param_config[\"n_layers\"]):\n",
+    "        block = model.blocks[l]\n",
+    "        att = block.att\n",
+    "        # Attention projections\n",
+    "        att.W_query.weight = assign(\n",
+    "            att.W_query.weight,\n",
+    "            params[f\"model.layers.{l}.self_attn.q_proj.weight\"],\n",
+    "            f\"model.layers.{l}.self_attn.q_proj.weight\",\n",
+    "        )\n",
+    "        att.W_key.weight = assign(\n",
+    "            att.W_key.weight,\n",
+    "            params[f\"model.layers.{l}.self_attn.k_proj.weight\"],\n",
+    "            f\"model.layers.{l}.self_attn.k_proj.weight\",\n",
+    "        )\n",
+    "        att.W_value.weight = assign(\n",
+    "            att.W_value.weight,\n",
+    "            params[f\"model.layers.{l}.self_attn.v_proj.weight\"],\n",
+    "            f\"model.layers.{l}.self_attn.v_proj.weight\",\n",
+    "        )\n",
+    "        att.out_proj.weight = assign(\n",
+    "            att.out_proj.weight,\n",
+    "            params[f\"model.layers.{l}.self_attn.o_proj.weight\"],\n",
+    "            f\"model.layers.{l}.self_attn.o_proj.weight\",\n",
+    "        )\n",
+    "        # QK normalization weights\n",
+    "        att.q_norm.scale = assign(\n",
+    "            att.q_norm.scale,\n",
+    "            params[f\"model.layers.{l}.self_attn.q_norm.weight\"],\n",
+    "            f\"model.layers.{l}.self_attn.q_norm.weight\",\n",
+    "        )\n",
+    "        att.k_norm.scale = assign(\n",
+    "            att.k_norm.scale,\n",
+    "            params[f\"model.layers.{l}.self_attn.k_norm.weight\"],\n",
+    "            f\"model.layers.{l}.self_attn.k_norm.weight\",\n",
+    "        )\n",
+    "        # Feed forward weights\n",
+    "        block.ff.fc1.weight = assign(\n",
+    "            block.ff.fc1.weight,\n",
+    "            params[f\"model.layers.{l}.mlp.gate_proj.weight\"],\n",
+    "            f\"model.layers.{l}.mlp.gate_proj.weight\",\n",
+    "        )\n",
+    "        block.ff.fc2.weight = assign(\n",
+    "            block.ff.fc2.weight,\n",
+    "            params[f\"model.layers.{l}.mlp.up_proj.weight\"],\n",
+    "            f\"model.layers.{l}.mlp.up_proj.weight\",\n",
+    "        )\n",
+    "        block.ff.fc3.weight = assign(\n",
+    "            block.ff.fc3.weight,\n",
+    "            params[f\"model.layers.{l}.mlp.down_proj.weight\"],\n",
+    "            f\"model.layers.{l}.mlp.down_proj.weight\",\n",
+    "        )\n",
+    "        # LayerNorm weights\n",
+    "        block.input_layernorm.scale = assign(\n",
+    "            block.input_layernorm.scale,\n",
+    "            params[f\"model.layers.{l}.input_layernorm.weight\"],\n",
+    "            f\"model.layers.{l}.input_layernorm.weight\",\n",
+    "        )\n",
+    "        block.post_attention_layernorm.scale = assign(\n",
+    "            block.post_attention_layernorm.scale,\n",
+    "            params[f\"model.layers.{l}.post_attention_layernorm.weight\"],\n",
+    "            f\"model.layers.{l}.post_attention_layernorm.weight\",\n",
+    "        )\n",
+    "        # Pre‑ and post‑feed forward norms\n",
+    "        pre_key = f\"model.layers.{l}.pre_feedforward_layernorm.weight\"\n",
+    "        post_key = f\"model.layers.{l}.post_feedforward_layernorm.weight\"\n",
+    "        if pre_key in params:\n",
+    "            block.pre_feedforward_layernorm.scale = assign(\n",
+    "                block.pre_feedforward_layernorm.scale,\n",
+    "                params[pre_key],\n",
+    "                pre_key,\n",
+    "            )\n",
+    "        if post_key in params:\n",
+    "            block.post_feedforward_layernorm.scale = assign(\n",
+    "                block.post_feedforward_layernorm.scale,\n",
+    "                params[post_key],\n",
+    "                post_key,\n",
+    "            )\n",
+    "\n",
+    "    # Final LayerNorm\n",
+    "    if \"model.norm.weight\" in params:\n",
+    "        model.final_norm.scale = assign(\n",
+    "            model.final_norm.scale,\n",
+    "            params[\"model.norm.weight\"],\n",
+    "            \"model.norm.weight\",\n",
+    "        )\n",
+    "    # Output head\n",
+    "    if \"lm_head.weight\" in params:\n",
+    "        model.out_head.weight = assign(\n",
+    "            model.out_head.weight,\n",
+    "            params[\"lm_head.weight\"],\n",
+    "            \"lm_head.weight\",\n",
+    "        )\n",
+    "    elif \"model.embed_tokens.weight\" in params:\n",
+    "        # Weight tying: reuse the embedding weights\n",
+    "        model.out_head.weight = assign(\n",
+    "            model.out_head.weight,\n",
+    "            params[\"model.embed_tokens.weight\"],\n",
+    "            \"model.embed_tokens.weight\",\n",
+    "        )"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "430340f2-78b9-4983-b74e-8395bbd7e574",
+   "metadata": {},
+   "source": [
+    "- Please note that Google requires that you accept the Gemma 3 licensing terms before you can download the files; to do this, you have to create a Hugging Face Hub account and visit the [google/gemma-3-270m]https://huggingface.co/google/gemma-3-270m) repository to accept the terms\n",
+    "- Next, you will need to create an access token; to generate an access token with READ permissions, click on the profile picture in the upper right and click on \"Settings\"\n",
+    "\n",
+    "\n",
+    "<img src=\"https://sebastianraschka.com/images/LLMs-from-scratch-images/bonus/gpt-to-llama/settings.webp?1\" width=\"300px\">\n",
+    "\n",
+    "- Then, create and copy the access token so you can copy & paste it into the next code cell\n",
+    "\n",
+    "<img src=\"https://sebastianraschka.com/images/LLMs-from-scratch-images/bonus/gpt-to-llama/access-token.webp?1\" width=\"600px\">"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 18,
+   "id": "7cee5292-f756-41dd-9b8d-c9b5c25d23f8",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Uncomment and run the following code if you are executing the notebook for the first time\n",
+    "\n",
+    "#from huggingface_hub import login\n",
+    "#login()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 19,
+   "id": "699cb1b8-a67d-49fb-80a6-0dad9d81f392",
+   "metadata": {
+    "colab": {
+     "base_uri": "https://localhost:8080/",
+     "height": 17,
+     "referenced_widgets": [
+      "9881b6995c3f49dc89e6992fd9ab660b",
+      "17a3174e65c54476b2e0d1faf8f011ca",
+      "1bbf2e62c0754d1593beb4105a7f1ac1",
+      "b82112e1dec645d98aa1c1ba64abcb61",
+      "271e2bd6a35e4a8b92de8697f7c0be5f",
+      "90a79523187446dfa692723b2e5833a7",
+      "431ffb83b8c14bf182f0430e07ea6154",
+      "a8f1b72a33dd4b548de23fbd95e0da18",
+      "25cc36132d384189acfbecc59483134b",
+      "bfd06423ad544218968648016e731a46",
+      "d029630b63ff44cf807ade428d2eb421"
+     ]
+    },
+    "id": "699cb1b8-a67d-49fb-80a6-0dad9d81f392",
+    "outputId": "55b2f28c-142f-4698-9d23-d27456d3ed6d"
+   },
+   "outputs": [],
+   "source": [
+    "import json\n",
+    "import os\n",
+    "from pathlib import Path\n",
+    "from safetensors.torch import load_file\n",
+    "from huggingface_hub import hf_hub_download, snapshot_download\n",
+    "\n",
+    "CHOOSE_MODEL = \"270m\"\n",
+    "\n",
+    "if USE_INSTRUCT_MODEL:\n",
+    "    repo_id = f\"google/gemma-3-{CHOOSE_MODEL}-it\"\n",
+    "else:\n",
+    "    repo_id = f\"google/gemma-3-{CHOOSE_MODEL}\"\n",
+    "\n",
+    "\n",
+    "local_dir = Path(repo_id).parts[-1]\n",
+    "\n",
+    "if CHOOSE_MODEL == \"270m\":\n",
+    "    weights_file = hf_hub_download(\n",
+    "        repo_id=repo_id,\n",
+    "        filename=\"model.safetensors\",\n",
+    "        local_dir=local_dir,\n",
+    "    )\n",
+    "    weights_dict = load_file(weights_file)\n",
+    "else:\n",
+    "    repo_dir = snapshot_download(repo_id=repo_id, local_dir=local_dir)\n",
+    "    index_path = os.path.join(repo_dir, \"model.safetensors.index.json\")\n",
+    "    with open(index_path, \"r\") as f:\n",
+    "        index = json.load(f)\n",
+    "\n",
+    "    weights_dict = {}\n",
+    "    for filename in set(index[\"weight_map\"].values()):\n",
+    "        shard_path = os.path.join(repo_dir, filename)\n",
+    "        shard = load_file(shard_path)\n",
+    "        weights_dict.update(shard)\n",
+    "\n",
+    "load_weights_into_gemma(model, GEMMA3_CONFIG_270M, weights_dict)\n",
+    "model.to(device)\n",
+    "del weights_dict"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "6b345491-3510-4397-92d3-cd0a3fa3deee",
+   "metadata": {},
+   "source": [
+    "&nbsp;\n",
+    "# 4. Load tokenizer"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 20,
+   "id": "b68ab489-48e5-471e-a814-56cda2d60f81",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from tokenizers import Tokenizer\n",
+    "\n",
+    "\n",
+    "class GemmaTokenizer:\n",
+    "    def __init__(self, tokenizer_file_path: str):\n",
+    "        tok_file = Path(tokenizer_file_path)\n",
+    "        self._tok = Tokenizer.from_file(str(tok_file))\n",
+    "        # Attempt to identify EOS and padding tokens\n",
+    "        eos_token = \"<end_of_turn>\"\n",
+    "        self.pad_token_id = eos_token\n",
+    "        self.eos_token_id = eos_token\n",
+    "\n",
+    "    def encode(self, text: str) -> list[int]:\n",
+    "        return self._tok.encode(text).ids\n",
+    "\n",
+    "    def decode(self, ids: list[int]) -> str:\n",
+    "        return self._tok.decode(ids, skip_special_tokens=False)\n",
+    "\n",
+    "\n",
+    "def apply_chat_template(user_text):\n",
+    "    return f\"<start_of_turn>user\\n{user_text}<end_of_turn>\\n<start_of_turn>model\\n\""
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 21,
+   "id": "7b6df8bc-7308-468e-93ce-2d5529ea7866",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "tokenizer_file_path = os.path.join(local_dir, \"tokenizer.json\")\n",
+    "if not os.path.exists(tokenizer_file_path):\n",
+    "    try:\n",
+    "        tokenizer_file_path = hf_hub_download(repo_id=repo_id, filename=\"tokenizer.json\", local_dir=local_dir)\n",
+    "    except Exception as e:\n",
+    "        print(f\"Warning: failed to download tokenizer.json: {e}\")\n",
+    "        tokenizer_file_path = \"tokenizer.json\"\n",
+    "\n",
+    "tokenizer = GemmaTokenizer(tokenizer_file_path=tokenizer_file_path)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 22,
+   "id": "1946b534-e3af-431a-a222-391a60bfa892",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'<bos><start_of_turn>user\\nGive me a short introduction to large language models.<end_of_turn>\\n<start_of_turn>model\\n'"
+      ]
+     },
+     "execution_count": 22,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "prompt = \"Give me a short introduction to large language models.\"\n",
+    "prompt = apply_chat_template(\"Give me a short introduction to large language models.\")\n",
+    "\n",
+    "\n",
+    "input_token_ids = tokenizer.encode(prompt)\n",
+    "text = tokenizer.decode(input_token_ids)\n",
+    "text"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "57d07df1-4401-4792-b549-7c4cc5632323",
+   "metadata": {
+    "id": "57d07df1-4401-4792-b549-7c4cc5632323"
+   },
+   "source": [
+    "&nbsp;\n",
+    "# 5. Generate text"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "id": "7b8401c6-e244-4cb7-9849-2ba71ce758d5",
+   "metadata": {
+    "id": "7b8401c6-e244-4cb7-9849-2ba71ce758d5"
+   },
+   "outputs": [],
+   "source": [
+    "def generate_text_basic_stream(model, token_ids, max_new_tokens, eos_token_id=None):\n",
+    "\n",
+    "    model.eval()\n",
+    "    with torch.no_grad():\n",
+    "        for _ in range(max_new_tokens):\n",
+    "            out = model(token_ids)[:, -1]\n",
+    "            next_token = torch.argmax(out, dim=-1, keepdim=True)\n",
+    "\n",
+    "            if (eos_token_id is not None\n",
+    "                   and torch.all(next_token == eos_token_id)):\n",
+    "               break\n",
+    "\n",
+    "            yield next_token\n",
+    "            \n",
+    "            token_ids = torch.cat([token_ids, next_token], dim=1)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 45,
+   "id": "1c7a04fa-6aac-416b-8f63-f1e19227633d",
+   "metadata": {
+    "id": "1c7a04fa-6aac-416b-8f63-f1e19227633d"
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Large language models (LLMs) are sophisticated artificial intelligence systems that can understand, generate, and manipulate human language. They are trained on massive amounts of text data to learn patterns and relationships within that data, enabling them to perform a wide range of tasks, from writing articles and answering questions to translating languages and summarizing information.\n"
+     ]
+    }
+   ],
+   "source": [
+    "input_token_ids_tensor = torch.tensor(input_token_ids, device=device).unsqueeze(0)\n",
+    "\n",
+    "\n",
+    "for token in generate_text_basic_stream(\n",
+    "    model=model,\n",
+    "    token_ids=input_token_ids_tensor,\n",
+    "    max_new_tokens=500,\n",
+    "    eos_token_id=tokenizer.encode(\"<end_of_turn>\")[-1]\n",
+    "):\n",
+    "    token_id = token.squeeze(0).tolist()\n",
+    "    print(\n",
+    "        tokenizer.decode(token_id),\n",
+    "        end=\"\",\n",
+    "        flush=True\n",
+    "    )"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "549324d6-5c71-4147-ae21-2e67675faa3d",
+   "metadata": {
+    "id": "549324d6-5c71-4147-ae21-2e67675faa3d"
+   },
+   "source": [
+    "&nbsp;\n",
+    "# What's next?"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "e6edaaae-2de1-406c-8ffa-897cdfa3808c",
+   "metadata": {
+    "id": "e6edaaae-2de1-406c-8ffa-897cdfa3808c"
+   },
+   "source": [
+    "- Check out the [README.md](./README.md), to use this model via the `llms_from_scratch` package\n",
+    "- For those interested in a comprehensive guide on building a large language model from scratch and gaining a deeper understanding of its mechanics, you might like my [Build a Large Language Model (From Scratch)](http://mng.bz/orYv)\n",
+    "\n",
+    "<a href=\"http://mng.bz/orYv\"><img src=\"https://sebastianraschka.com/images/LLMs-from-scratch-images/cover-small.webp\" width=\"100px\"></a>"
+   ]
+  }
+ ],
+ "metadata": {
+  "accelerator": "GPU",
+  "colab": {
+   "gpuType": "A100",
+   "provenance": []
+  },
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.10.16"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

ch05/12_gemma3/tests/test_gemma3.py

@@ -0,0 +1,178 @@
+# Copyright (c) Sebastian Raschka under Apache License 2.0 (see LICENSE.txt).
+# Source for "Build a Large Language Model From Scratch"
+#   - https://www.manning.com/books/build-a-large-language-model-from-scratch
+# Code: https://github.com/rasbt/LLMs-from-scratch
+
+import importlib
+import types
+import re
+from pathlib import Path
+
+import nbformat
+import pytest
+import torch
+
+transformers_installed = importlib.util.find_spec("transformers") is not None
+
+
+def _extract_defs_and_classes_from_code(src):
+    lines = src.splitlines()
+    kept = []
+    i = 0
+    while i < len(lines):
+        line = lines[i]
+        stripped = line.lstrip()
+        # Keep decorators attached to the next def/class
+        if stripped.startswith("@"):
+            # Look ahead: if the next non-empty line starts with def/class, keep decorator
+            j = i + 1
+            while j < len(lines) and not lines[j].strip():
+                j += 1
+            if j < len(lines) and lines[j].lstrip().startswith(("def ", "class ")):
+                kept.append(line)
+                i += 1
+                continue
+        if stripped.startswith("def ") or stripped.startswith("class "):
+            kept.append(line)
+            # capture until we leave the indentation block
+            base_indent = len(line) - len(stripped)
+            i += 1
+            while i < len(lines):
+                nxt = lines[i]
+                if nxt.strip() == "":
+                    kept.append(nxt)
+                    i += 1
+                    continue
+                indent = len(nxt) - len(nxt.lstrip())
+                if indent <= base_indent and not nxt.lstrip().startswith(("#", "@")):
+                    break
+                kept.append(nxt)
+                i += 1
+            continue
+        i += 1
+    code = "\n".join(kept)
+    code = re.sub(r"def\s+load_weights_into_gemma\s*\(\s*Gemma3Model\s*,",
+                  "def load_weights_into_gemma(model,",
+                  code)
+    return code
+
+
+def import_definitions_from_notebook(nb_dir_or_path, notebook_name):
+    nb_path = Path(nb_dir_or_path)
+    if nb_path.is_dir():
+        nb_file = nb_path / notebook_name
+    else:
+        nb_file = nb_path
+    if not nb_file.exists():
+        raise FileNotFoundError(f"Notebook not found: {nb_file}")
+
+    nb = nbformat.read(nb_file, as_version=4)
+    pieces = ["import torch", "import torch.nn as nn"]
+    for cell in nb.cells:
+        if cell.cell_type == "code":
+            pieces.append(_extract_defs_and_classes_from_code(cell.source))
+    src = "\n\n".join(pieces)
+
+    mod = types.ModuleType("gemma3_defs")
+    exec(src, mod.__dict__)
+    return mod
+
+
+@pytest.fixture
+def dummy_input():
+    torch.manual_seed(123)
+    return torch.randint(0, 100, (1, 8))  # batch size 1, seq length 8
+
+
+@pytest.fixture
+def dummy_cfg_base():
+    return {
+        "vocab_size": 100,
+        "emb_dim": 32,
+        "hidden_dim": 64,
+        "n_layers": 2,
+        "n_heads": 4,
+        "head_dim": 8,
+        "n_kv_groups": 1,
+        "qk_norm": True,                # Gemma3 uses q/k RMSNorm
+        "dtype": torch.float32,
+        "rope_base": 1_000_000.0,       # global RoPE base
+        "rope_local_base": 10_000.0,    # local RoPE base (unused in these tests)
+        "context_length": 64,
+        "sliding_window": 16,
+        "layer_types": ["full_attention", "full_attention"],
+        "query_pre_attn_scalar": 256,
+    }
+
+
+@torch.inference_mode()
+def test_dummy_gemma3_forward(dummy_cfg_base, dummy_input):
+    nb_dir = Path(__file__).resolve().parents[1]
+    mod = import_definitions_from_notebook(nb_dir, "standalone-gemma3.ipynb")
+    Gemma3Model = mod.Gemma3Model
+
+    torch.manual_seed(123)
+    model = Gemma3Model(dummy_cfg_base)
+    out = model(dummy_input)
+    assert out.shape == (1, dummy_input.size(1), dummy_cfg_base["vocab_size"]),         f"Expected shape (1, seq_len, vocab_size), got {out.shape}"
+
+
+@torch.inference_mode()
+@pytest.mark.skipif(not transformers_installed, reason="transformers not installed")
+def test_gemma3_base_equivalence_with_transformers():
+    nb_dir = Path(__file__).resolve().parents[1]
+    mod = import_definitions_from_notebook(nb_dir, "standalone-gemma3.ipynb")
+    Gemma3Model = mod.Gemma3Model
+    load_weights_into_gemma = mod.load_weights_into_gemma
+
+    from transformers import Gemma3TextConfig, Gemma3ForCausalLM
+
+    # Tiny config so the test is fast
+    cfg = {
+        "vocab_size": 257,
+        "context_length": 8,
+        "emb_dim": 32,
+        "n_heads": 4,
+        "n_layers": 2,
+        "hidden_dim": 64,
+        "head_dim": 8,
+        "qk_norm": True,
+        "n_kv_groups": 2,
+        "rope_base": 1_000_000.0,
+        "rope_local_base": 10_000.0,
+        "sliding_window": 4,
+        "layer_types": ["full_attention", "full_attention"],
+        "dtype": torch.float32,
+        "query_pre_attn_scalar": 256,
+    }
+    model = Gemma3Model(cfg)
+
+    hf_cfg = Gemma3TextConfig(
+        vocab_size=cfg["vocab_size"],
+        max_position_embeddings=cfg["context_length"],
+        hidden_size=cfg["emb_dim"],
+        num_attention_heads=cfg["n_heads"],
+        num_hidden_layers=cfg["n_layers"],
+        intermediate_size=cfg["hidden_dim"],
+        head_dim=cfg["head_dim"],
+        num_key_value_heads=cfg["n_kv_groups"],
+        rope_theta=cfg["rope_base"],
+        rope_local_base_freq=cfg["rope_local_base"],
+        layer_types=cfg["layer_types"],
+        sliding_window=cfg["sliding_window"],
+        tie_word_embeddings=False,
+        attn_implementation="eager",
+        torch_dtype=torch.float32,
+        query_pre_attn_scalar=cfg["query_pre_attn_scalar"],
+        rope_scaling={"rope_type": "default"},
+    )
+    hf_model = Gemma3ForCausalLM(hf_cfg)
+
+    hf_state = hf_model.state_dict()
+    param_config = {"n_layers": cfg["n_layers"], "hidden_dim": cfg["hidden_dim"]}
+    load_weights_into_gemma(model, param_config, hf_state)
+
+    x = torch.randint(0, cfg["vocab_size"], (2, cfg["context_length"]), dtype=torch.long)
+    ours_logits = model(x)
+    theirs_logits = hf_model(x).logits
+    torch.testing.assert_close(ours_logits, theirs_logits, rtol=1e-5, atol=1e-5)