[Docs] Add Qwen3.5 to Key Models (#2502)

SUMMARY:
- Example walkthrough 
- Notes about transformers version
- Should land
https://github.com/vllm-project/llm-compressor/pulls/dsikka to make
these examples make sense

Author: dsikka

docs/.nav.yml

@@ -19,6 +19,10 @@ nav:
     - Qwen3:
       - key-models/qwen3/index.md
       - FP8 Example: key-models/qwen3/fp8-example.md
+    - Qwen3.5:
+      - key-models/qwen3.5/index.md
+      - NVFP4A16 VL Example: key-models/qwen3.5/nvfp4-vl-example.md
+      - NVFP4 MoE Example: key-models/qwen3.5/nvfp4-moe-example.md
     - Kimi-K2:
       - key-models/kimi-k2/index.md
       - FP8 Example: key-models/kimi-k2/fp8-example.md

docs/key-models/index.md

@@ -1,6 +1,6 @@
 # Key Models
 
-The following models are among the most commonly used with LLM Compressor: Llama 4, Qwen3, Kimi-K2, and Mistral Large 3. Each model page contains quantization examples with tested configurations and recommended parameters.
+The following models are among the most commonly used with LLM Compressor: Llama 4, Qwen3, Qwen3.5, Kimi-K2, and Mistral Large 3. Each model page contains quantization examples with tested configurations and recommended parameters.
 
 <div class="grid cards" markdown>
 
@@ -20,6 +20,14 @@ The following models are among the most commonly used with LLM Compressor: Llama
 
       [:octicons-arrow-right-24: Qwen3](qwen3/index.md)
 
+  - **Qwen3.5**
+
+      ---
+
+      Qwen3.5 dense vision-language and sparse MoE models.
+
+      [:octicons-arrow-right-24: Qwen3.5](qwen3.5/index.md)
+
   - **Kimi-K2**
 
       ---

docs/key-models/qwen3.5/index.md

@@ -0,0 +1,12 @@
+# Qwen3.5
+
+Quantization examples for the Qwen3.5 family of models, including dense vision-language and sparse MoE variants.
+
+> **Note:** These examples require `transformers >= v5`, which can be installed with:
+> ```bash
+> uv pip install --upgrade transformers
+> ```
+> With this, the examples can run end-to-end on `main`. You may also need to update the version of `transformers` in your vLLM environment in order for the tokenizer to be properly applied.
+
+- [NVFP4A16 Vision-Language Example](nvfp4-vl-example.md)
+- [NVFP4 MoE Example](nvfp4-moe-example.md)

docs/key-models/qwen3.5/nvfp4-moe-example.md

@@ -0,0 +1,123 @@
+## Qwen3.5 NVFP4 MoE Example
+
+This example quantizes the Qwen3.5-122B-A10B sparse MoE model to NVFP4 (weights and activations quantized to FP4) using calibration data.
+
+NOTE: This example requires `transformers >= v5`.
+
+### Code Walkthrough
+
+Let's walk through the main steps of the quantization process:
+1. Load model
+2. Load and preprocess calibration dataset
+3. Configure quantization algorithm and scheme
+4. Apply quantization
+5. Save to disk in compressed-tensors format
+
+### 1. Load Model
+
+```python
+import torch
+from compressed_tensors.utils import save_mtp_tensors_to_checkpoint
+from datasets import load_dataset
+from transformers import AutoProcessor, Qwen3_5MoeForConditionalGeneration
+
+from llmcompressor import oneshot
+from llmcompressor.modifiers.quantization import QuantizationModifier
+
+MODEL_ID = "Qwen/Qwen3.5-122B-A10B"
+
+# Load model.
+model = Qwen3_5MoeForConditionalGeneration.from_pretrained(MODEL_ID, dtype="auto")
+processor = AutoProcessor.from_pretrained(MODEL_ID)
+```
+
+### 2. Load and Preprocess Calibration Dataset
+
+```python
+NUM_CALIBRATION_SAMPLES = 256
+MAX_SEQUENCE_LENGTH = 4096
+
+ds = load_dataset(
+    "HuggingFaceH4/ultrachat_200k",
+    split=f"train_sft[:{NUM_CALIBRATION_SAMPLES}]",
+)
+ds = ds.select_columns(["messages"])
+ds = ds.shuffle(seed=42)
+
+
+def preprocess_function(example):
+    messages = [
+        {"role": m["role"], "content": [{"type": "text", "text": m["content"]}]}
+        for m in example["messages"]
+    ]
+    return processor.apply_chat_template(
+        messages,
+        return_tensors="pt",
+        padding=False,
+        truncation=True,
+        max_length=MAX_SEQUENCE_LENGTH,
+        tokenize=True,
+        add_special_tokens=False,
+        return_dict=True,
+        add_generation_prompt=False,
+    )
+
+
+ds = ds.map(preprocess_function, batched=False, remove_columns=ds.column_names)
+
+
+def data_collator(batch):
+    assert len(batch) == 1
+    return {key: torch.tensor(value) for key, value in batch[0].items()}
+```
+
+### 3. Configure Quantization Algorithm and Scheme
+
+In this case, we are doing the following:
+- Quantize the weights and activations to FP4 via calibration-based PTQ
+- Skip `lm_head`, visual layers, MoE gate projections, embedding layers, shared expert gates, and linear attention layers
+- MTP layers are not loaded through `Qwen3_5MoeForConditionalGeneration`, so there is no need to include them in the ignore list
+
+```python
+recipe = QuantizationModifier(
+    targets="Linear",
+    scheme="NVFP4",
+    ignore=[
+        "re:.*lm_head",
+        "re:visual.*",
+        "re:model.visual.*",
+        "re:.*mlp.gate$",
+        "re:.*embed_tokens$",
+        "re:.*shared_expert_gate$",
+        "re:.*linear_attn.*",
+    ],
+)
+```
+
+### 4. Apply Quantization
+
+`moe_calibrate_all_experts=True` ensures all MoE experts receive calibration data, which improves quantization quality for sparse MoE models.
+
+```python
+oneshot(
+    model=model,
+    recipe=recipe,
+    dataset=ds,
+    max_seq_length=MAX_SEQUENCE_LENGTH,
+    num_calibration_samples=NUM_CALIBRATION_SAMPLES,
+    moe_calibrate_all_experts=True,
+    data_collator=data_collator,
+)
+```
+
+### 5. Save to Disk in Compressed-Tensors Format
+
+```python
+SAVE_DIR = MODEL_ID.rstrip("/").split("/")[-1] + "-NVFP4"
+model.save_pretrained(SAVE_DIR)
+processor.save_pretrained(SAVE_DIR)
+
+# MTP layers are excluded from the model through Qwen3_5MoeForConditionalGeneration
+# Save them as-is from the original checkpoint into the quantized output.
+save_mtp_tensors_to_checkpoint(source_model=MODEL_ID, dest_dir=SAVE_DIR)
+```

docs/key-models/qwen3.5/nvfp4-vl-example.md

@@ -0,0 +1,84 @@
+## Qwen3.5 NVFP4A16 Vision-Language Example
+
+This example quantizes the Qwen3.5-27B vision-language model to NVFP4A16 (weights quantized to FP4 with per-group-16 granularity, activations in FP16) using data-free PTQ.
+
+### Code Walkthrough
+
+Let's walk through the main steps of the quantization process:
+1. Load model
+2. Configure quantization algorithm and scheme
+3. Apply quantization
+4. Run sample generation
+5. Save to disk in compressed-tensors format
+
+### 1. Load Model
+
+```python
+from compressed_tensors.offload import dispatch_model
+from compressed_tensors.utils import save_mtp_tensors_to_checkpoint
+from transformers import AutoProcessor, Qwen3_5ForConditionalGeneration
+
+from llmcompressor import oneshot
+from llmcompressor.modifiers.quantization import QuantizationModifier
+
+# Load model.
+MODEL_ID = "Qwen/Qwen3.5-27B"
+model = Qwen3_5ForConditionalGeneration.from_pretrained(
+    MODEL_ID, dtype="auto", trust_remote_code=True
+)
+processor = AutoProcessor.from_pretrained(MODEL_ID, trust_remote_code=True)
+```
+
+### 2. Configure Quantization Algorithm and Scheme
+
+In this case, we are doing the following:
+- Quantize the weights to FP4 with per-group-16 granularity via data-free PTQ
+- Skip the visual encoder, `lm_head`, and linear attention layers (Gated DeltaNet fused projections are incompatible with NVFP4)
+- MTP layers are not loaded through `Qwen3_5ForConditionalGeneration`, so there is no need to include them in the ignore list
+
+```python
+# No need to include mtp layers as they are not loaded
+# through Qwen3_5ForConditionalGeneration
+recipe = QuantizationModifier(
+    targets="Linear",
+    scheme="NVFP4A16",
+    ignore=[
+        "lm_head",
+        "re:.*visual.*",
+        "re:.*linear_attn.*",
+    ],
+)
+```
+
+### 3. Apply Quantization
+
+```python
+oneshot(model=model, recipe=recipe)
+```
+
+### 4. Run Sample Generation
+
+```python
+print("\n\n========== SAMPLE GENERATION ==============")
+dispatch_model(model)
+messages = [{"role": "user", "content": "Hello my name is"}]
+prompt = processor.apply_chat_template(
+    messages, tokenize=False, add_generation_prompt=True
+)
+inputs = processor(text=prompt, return_tensors="pt").to(model.device)
+output = model.generate(**inputs, max_new_tokens=100)
+print(processor.decode(output[0], skip_special_tokens=True))
+print("==========================================\n\n")
+```
+
+### 5. Save to Disk in Compressed-Tensors Format
+
+```python
+SAVE_DIR = MODEL_ID.rstrip("/").split("/")[-1] + "-NVFP4A16"
+model.save_pretrained(SAVE_DIR)
+processor.save_pretrained(SAVE_DIR)
+
+# MTP layers are excluded from the model through Qwen3_5ForConditionalGeneration
+# Save them as-is from the original checkpoint into the quantized output.
+save_mtp_tensors_to_checkpoint(source_model=MODEL_ID, dest_dir=SAVE_DIR)
+```