diff --git a/aider/args.py b/aider/args.py
index 6b97ea13f..bc3e36ff0 100644
--- a/aider/args.py
+++ b/aider/args.py
@@ -140,7 +140,7 @@ def get_parser(default_config_files, git_root):
         metavar="MODEL_FILE",
         default=None,
         help={
-            "File with model definitions to be registered for info/cost, json formated",
+            "Specify a file with model definitions (info and cost) to be registered with litellm, json formated",
             "  {"
             "    \"gpt-4\": {",
             "      \"max_tokens\": 8192,",
diff --git a/website/docs/install/optional.md b/website/docs/install/optional.md
index c33a8980e..f79ac856b 100644
--- a/website/docs/install/optional.md
+++ b/website/docs/install/optional.md
@@ -26,6 +26,27 @@ Put a line in it like this to specify your api key:
 openai-api-key: sk-...
 ```
 
+## Registering Models not in litellm 
+
+You can register models info and cost with litellm by adding one or more of the following files
+* {HomeDir}/.aider.models.json
+* {GitRoot}/.aider.models.json
+* {CWD}/.aider.models.json
+* or via the command line argument `model-file`
+If the files above exists, they will be loaded in that order. Files loaded last will take priority.
+The json file should be formated as follows
+```
+{
+  "gpt-4": {
+    "max_tokens": 8192,
+    "input_cost_per_token": 0.00003,
+    "output_cost_per_token": 0.00006,
+    "litellm_provider": "openai",
+    "mode": "chat",
+  },
+}
+```
+
 ## Enable Playwright 
 
 Aider supports adding web pages to the chat with the `/web <url>` command.
diff --git a/website/docs/options.md b/website/docs/options.md
index 27d2df7c2..7d70e58d2 100644
--- a/website/docs/options.md
+++ b/website/docs/options.md
@@ -103,6 +103,10 @@ Aliases:
 List known models which match the (partial) MODEL name  
 Environment variable: `AIDER_MODELS`  
 
+### `--model-file FILE`
+Specify a file with model definitions (info and cost) to be registered with litellm, json formated. See [Registering Models not in litellm](install/optional.md#registering_models_not_in_litellm) for the format  
+Environment variable: `AIDER_MODEL_FILE`
+
 ### `--openai-api-base OPENAI_API_BASE`
 Specify the api base url  
 Environment variable: `OPENAI_API_BASE`