docs: expand aliases section in add_model_pricing guide

Add usage example with concrete model entry, explanation of load-time
expansion, and cross-reference to model_alias_map to clarify the
difference between the two features.

docs/my-website/docs/provider_registration/add_model_pricing.md

@@ -122,4 +122,28 @@ Here's the full specification with all available fields:
 }
 ```
 
-That's it! Your PR will be reviewed and merged.
+### Using Aliases
+
+Many providers release the same model under multiple names — for example, a `latest` tag and a dated version like `claude-sonnet-4-5-20250929`. Instead of duplicating the entire entry, you can use the `aliases` field:
+
+```json
+{
+    "claude-sonnet-4-5": {
+        "aliases": ["claude-sonnet-4-5-20250929"],
+        "input_cost_per_token": 3e-06,
+        "output_cost_per_token": 1.5e-05,
+        "litellm_provider": "anthropic",
+        "max_input_tokens": 200000,
+        "max_output_tokens": 64000,
+        "mode": "chat",
+        "supports_function_calling": true,
+        "supports_tool_choice": true
+    }
+}
+```
+
+At load time, each alias is expanded into a top-level entry sharing the same data as the canonical entry. The example above makes both `claude-sonnet-4-5` and `claude-sonnet-4-5-20250929` resolve with the same pricing and capabilities.
+
+:::info
+This is different from [`model_alias_map`](../completion/model_alias.md), which is a runtime SDK/proxy feature for mapping user-facing model names to LiteLLM model identifiers. The `aliases` field here is for the model cost JSON only — it avoids duplicate entries for models that share identical pricing and capabilities.
+:::