diff --git a/vllm/config/model_arch.py b/vllm/config/model_arch.py
index 6d9e32a24c5c8..1bf72fe91f646 100644
--- a/vllm/config/model_arch.py
+++ b/vllm/config/model_arch.py
@@ -17,8 +17,9 @@ class ModelArchitectureConfig:
     Configuration for model architecture that required by vLLM runtime
     """
 
-    architectures: list[str]
-    """List of model architecture class names (e.g., ['LlamaForCausalLM'])."""
+    architectures: list[str] | None
+    """List of model architecture class names (e.g., ['LlamaForCausalLM']).
+       It can be None upon calling `vllm_config.with_hf_config(config.text_config)`"""
 
     model_type: str
     """Model type identifier (e.g., 'llama', 'gpt_oss')."""