diff --git a/aider/args.py b/aider/args.py
index 389de7435..2c10f8497 100644
--- a/aider/args.py
+++ b/aider/args.py
@@ -141,6 +141,23 @@ def get_parser(default_config_files, git_root):
         env_var="OPENAI_ORGANIZATION_ID",
         help="Specify the OpenAI organization ID",
     )
+    group.add_argument(
+        "--model-file",
+        metavar="MODEL_FILE",
+        default=None,
+        help={
+            "Specify a file with model definitions (info and cost) to be registered with litellm, json formated",
+            "  {"
+            "    \"gpt-4\": {",
+            "      \"max_tokens\": 8192,",
+            "      \"input_cost_per_token\": 0.00003,",
+            "      \"output_cost_per_token\": 0.00006,",
+            "      \"litellm_provider\": \"openai\",",
+            "      \"mode\": \"chat\"",
+            "    },",
+            "  }"
+        }
+    )
     group.add_argument(
         "--edit-format",
         metavar="EDIT_FORMAT",
diff --git a/aider/main.py b/aider/main.py
index 31b3f0ce3..2447efe8e 100644
--- a/aider/main.py
+++ b/aider/main.py
@@ -336,6 +336,26 @@ def main(argv=None, input=None, output=None, force_git_root=None, return_coder=F
     if args.openai_organization_id:
         os.environ["OPENAI_ORGANIZATION"] = args.openai_organization_id
 
+    model_def_files = []
+    model_def_fname = Path(".aider.models.json")
+    model_def_files.append(Path.home() / model_def_fname)  # homedir
+    if git_root:
+        model_def_files.append(Path(git_root) / model_def_fname)  # git root
+    if args.model_file:
+        model_def_files.append(args.model_file)
+    model_def_files.append(model_def_fname.resolve())
+    model_def_files = list(map(str, model_def_files))
+    model_def_files = list(dict.fromkeys(model_def_files))
+    try:
+        model_files_loaded=models.register_models(model_def_files)
+        if len(model_files_loaded) > 0:
+            io.tool_output(f"Loaded {len(model_files_loaded)} model file(s)")
+            for model_file in model_files_loaded:
+                io.tool_output(f"  - {model_file}")
+    except Exception as e:
+        io.tool_error(f"Error loading model info/cost: {e}")
+        return 1
+
     main_model = models.Model(args.model, weak_model=args.weak_model)
 
     lint_cmds = parse_lint_cmds(args.lint_cmd, io)
diff --git a/aider/models.py b/aider/models.py
index 5884ff31f..18e03eb60 100644
--- a/aider/models.py
+++ b/aider/models.py
@@ -426,6 +426,21 @@ class Model:
 
         return res
 
+def register_models(model_def_fnames):
+    model_files_loaded = []
+    for model_def_fname in model_def_fnames:
+        if not os.path.exists(model_def_fname):
+            continue
+        model_files_loaded.append(model_def_fname)
+        try:
+            with open(model_def_fname, "r") as model_def_file:
+                model_def = json.load(model_def_file)
+        except json.JSONDecodeError as e:
+            raise Exception(f"Error loading model definition from {model_def_fname}: {e}")
+
+        litellm.register_model(model_def)
+
+    return model_files_loaded
 
 def validate_variables(vars):
     missing = []
diff --git a/website/docs/install/optional.md b/website/docs/install/optional.md
index c33a8980e..acf043209 100644
--- a/website/docs/install/optional.md
+++ b/website/docs/install/optional.md
@@ -26,6 +26,28 @@ Put a line in it like this to specify your api key:
 openai-api-key: sk-...
 ```
 
+## Registering Models not in litellm 
+
+You can register model info and costs 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",
+  },
+}
+```
+see [litellm's model definitions](https://github.com/BerriAI/litellm/blob/main/model_prices_and_context_window.json) for examples
+
 ## 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 b40fbcc4a..4482e1cb4 100644
--- a/website/docs/options.md
+++ b/website/docs/options.md
@@ -108,6 +108,10 @@ 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`