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docs/contributing/model/registration.md

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+# Registering a Model
+
+vLLM relies on a model registry to determine how to run each model.
+A list of pre-registered architectures can be found [here](../../models/supported_models.md).
+
+If your model is not on this list, you must register it to vLLM.
+This page provides detailed instructions on how to do so.
+
+## Built-in models
+
+To add a model directly to the vLLM library, start by forking our [GitHub repository](https://github.com/vllm-project/vllm) and then [build it from source](../../getting_started/installation/gpu.md#build-wheel-from-source).
+This gives you the ability to modify the codebase and test your model.
+
+After you have implemented your model (see [tutorial](basic.md)), put it into the [vllm/model_executor/models](../../../vllm/model_executor/models) directory.
+Then, add your model class to `_VLLM_MODELS` in [vllm/model_executor/models/registry.py](../../../vllm/model_executor/models/registry.py) so that it is automatically registered upon importing vLLM.
+Finally, update our [list of supported models](../../models/supported_models.md) to promote your model!
+
+!!! important
+    The list of models in each section should be maintained in alphabetical order.
+
+## Out-of-tree models
+
+You can load an external model [using a plugin](../../design/plugin_system.md) without modifying the vLLM codebase.
+
+To register the model, use the following code:
+
+```python
+# The entrypoint of your plugin
+def register():
+    from vllm import ModelRegistry
+    from your_code import YourModelForCausalLM
+
+    ModelRegistry.register_model("YourModelForCausalLM", YourModelForCausalLM)
+```
+
+If your model imports modules that initialize CUDA, consider lazy-importing it to avoid errors like `RuntimeError: Cannot re-initialize CUDA in forked subprocess`:
+
+```python
+# The entrypoint of your plugin
+def register():
+    from vllm import ModelRegistry
+
+    ModelRegistry.register_model(
+        "YourModelForCausalLM",
+        "your_code:YourModelForCausalLM",
+    )
+```
+
+!!! important
+    If your model is a multimodal model, ensure the model class implements the [SupportsMultiModal][vllm.model_executor.models.interfaces.SupportsMultiModal] interface.
+    Read more about that [here](multimodal.md).