chore: import upstream snapshot with attribution

2026-07-13 12:55:37 +08:00
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+# Hidden State Extraction
+
+The Hidden State Extraction feature allows vLLM to save intermediate layer activations from a target model during inference. This is useful for training [EAGLE](eagle.md)-style draft models, knowledge distillation, or offline analysis of model internals.
+
+!!! note
+    It is possible to save the last-layer's output hidden states by passing `num_hidden_layers` as a layer id. Note that these are _not_ normalized using the output norm.
+
+## Offline Example
+
+```python
+import tempfile
+
+from vllm import LLM, SamplingParams
+from vllm.config.kv_transfer import KVTransferConfig
+from vllm.distributed.kv_transfer.kv_connector.v1 import (
+    example_hidden_states_connector,
+)
+
+with tempfile.TemporaryDirectory() as tmpdir:
+    llm = LLM(
+        model="Qwen/Qwen3-8B",
+        speculative_config={
+            "method": "extract_hidden_states",
+            "num_speculative_tokens": 1,
+            "draft_model_config": {
+                "hf_config": {
+                    "eagle_aux_hidden_state_layer_ids": [1, 2, 3, 4],
+                },
+            },
+        },
+        kv_transfer_config=KVTransferConfig(
+            kv_connector="ExampleHiddenStatesConnector",
+            kv_role="kv_producer",
+            kv_connector_extra_config={
+                "shared_storage_path": tmpdir,
+            },
+        ),
+    )
+
+    outputs = llm.generate(
+        ["The future of AI is"],
+        SamplingParams(max_tokens=1),
+    )
+
+    for output in outputs:
+        path = output.kv_transfer_params["hidden_states_path"]
+        obj = example_hidden_states_connector.load_hidden_states(path)
+        print(f"token_ids: {obj['token_ids'].shape}")
+        print(f"hidden_states: {obj['hidden_states'].shape}")
+```
+
+A complete example is available at [`examples/features/speculative_decoding/extract_hidden_states_offline.py`](../../../examples/features/speculative_decoding/extract_hidden_states_offline.py).
+
+## Online Example
+
+For improved performance, it is recommended to use a RAM-mounted file system such as `/dev/shm/` for online usage in which the client cleans up the files soon after they are generated.
+
+```bash
+vllm serve Qwen/Qwen3-8B \
+    --speculative_config '{"method": "extract_hidden_states", "num_speculative_tokens": 1, "draft_model_config": {"hf_config": {"eagle_aux_hidden_state_layer_ids": [1, 2, 3, 4]}}}' \
+    --kv_transfer_config '{"kv_connector": "ExampleHiddenStatesConnector", "kv_role": "kv_producer", "kv_connector_extra_config": {"shared_storage_path": "/dev/shm/hidden_states"}}'
+```
+
+## Per-Request Options
+
+Both offline and online modes support per-request options via `kv_transfer_params`:
+
+| Parameter | Default | Description |
+| --- | --- | --- |
+| `hidden_states_path` | Auto-generated | Custom file path for saving hidden states. If not set, files are saved to `<shared_storage_path>/<request_id>.safetensors`. Requires `allow_custom_save_path` to be enabled in the server config. |
+| `include_output_tokens` | `False` | When `True`, save hidden states for both prompt and generated output tokens. When `False`, only prompt token hidden states are saved. |
+
+### Offline usage
+
+Pass per-request options via `extra_args` on `SamplingParams`:
+
+```python
+SamplingParams(
+    max_tokens=32,
+    extra_args={
+        "kv_transfer_params": {
+            "hidden_states_path": "/tmp/my_output.safetensors",
+            "include_output_tokens": True,
+        }
+    },
+)
+```
+
+### Online usage
+
+Pass `kv_transfer_params` as a top-level field in the API request:
+
+```json
+{
+    "model": "Qwen/Qwen3-8B",
+    "messages": [{"role": "user", "content": "Hello"}],
+    "max_tokens": 32,
+    "kv_transfer_params": {
+        "hidden_states_path": "/tmp/my_output.safetensors",
+        "include_output_tokens": true
+    }
+}
+```
+
+## Configuration
+
+The `kv_connector_extra_config` dict accepts these server-level options:
+
+| Parameter | Default | Description |
+| --- | --- | --- |
+| `shared_storage_path` | `/tmp` | Directory where hidden state files are saved (used when `hidden_states_path` is not set per-request) |
+| `allow_custom_save_path` | `False` | Allow API clients to specify custom file paths via `hidden_states_path`. When disabled, client-provided paths are ignored with a warning. Enable only with trusted clients — custom paths can write to arbitrary locations on the server. |
+| `num_writer_threads` | `8` | Thread pool size for async disk writes |
+| `use_synchronization_lock` | `True` | Use file locks so concurrent readers block until writes complete. Can be disabled for batch generation where synchronization is not needed. |
+
+## Output Format
+
+Each request produces a `.safetensors` file containing:
+
+- **`hidden_states`** — shape `[num_tokens, num_extracted_layers, hidden_size]`
+- **`token_ids`** — shape `[num_tokens]`
+
+The file path is returned in `output.kv_transfer_params["hidden_states_path"]`. Use `load_hidden_states()` from the connector module to read the file with proper synchronization.
+
+!!! note
+    Chunked prefill is not compatible with this feature and must be disabled.