diff --git a/ChangeLog.md b/ChangeLog.md
index 5f8dfb65c0a..e7407bf25ed 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -9,6 +9,7 @@ Modelerfour version: 4.15.378
 - Correctly have default behavior of csv for array query parameters when collection format is not specified in the swagger
 (taken from m4 update - perks PR #118)
 - Fix bug when generating parameters with client default value and constant schema  #707
+- Make operation mixin signatures for multiapi default to default api version  #715
 - Fix name in setup.py to default to `package-name` if set  #721
 
 ### 2020-07-07 - 5.1.0-preview.4
diff --git a/autorest/multiapi/__init__.py b/autorest/multiapi/__init__.py
index d687acfbe22..70b1af5b5eb 100644
--- a/autorest/multiapi/__init__.py
+++ b/autorest/multiapi/__init__.py
@@ -169,7 +169,36 @@ def _get_paths_to_versions(self) -> List[Path]:
                 paths_to_versions.append(Path(child.stem))
         return paths_to_versions
 
-    def _build_operation_mixin_meta(self, paths_to_versions: List[Path]) -> Dict[str, Dict[str, Dict[str, Any]]]:
+    def _make_signature_of_mixin_based_on_default_api_version(
+        self,
+        mixin_operations: Dict[str, Dict[str, Dict[str, Any]]],
+        last_api_version_path: Path
+    ) -> Dict[str, Dict[str, Dict[str, Any]]]:
+        metadata_json = json.loads(self._autorestapi.read_file(last_api_version_path / "_metadata.json"))
+        if not metadata_json.get('operation_mixins'):
+            return mixin_operations
+        for func_name, func in metadata_json['operation_mixins'].items():
+            if func_name.startswith("_"):
+                continue
+
+            mixin_operations.setdefault(func_name, {}).setdefault('sync', {})
+            mixin_operations.setdefault(func_name, {}).setdefault('async', {})
+            mixin_operations[func_name]['sync'].update({
+                "signature": func['sync']['signature'],
+                "doc": func['sync']['doc'],
+                "call": func['call']
+            })
+            mixin_operations[func_name]['async'].update({
+                "signature": func['async']['signature'],
+                "coroutine": func['async']['coroutine'],
+                "doc": func['async']['doc'],
+                "call": func['call']
+            })
+        return mixin_operations
+
+    def _build_operation_mixin_meta(
+        self, paths_to_versions: List[Path], last_api_version: str
+    ) -> Dict[str, Dict[str, Dict[str, Any]]]:
         """Introspect the client:
 
         version_dict => {
@@ -212,8 +241,14 @@ def _build_operation_mixin_meta(self, paths_to_versions: List[Path]) -> Dict[str
                     "available_apis", []
                 ).append(version_path.name)
 
-
-        return mixin_operations
+        # make sure that the signature, doc, call, and coroutine is based off of the default api version,
+        # if the default api version has a definition for it.
+        # will hopefully get this removed once we deal with mixin operations with different signatures
+        # for different api versions
+        last_api_version_path = [
+            version_path for version_path in paths_to_versions if version_path.name == last_api_version
+        ][0]
+        return self._make_signature_of_mixin_based_on_default_api_version(mixin_operations, last_api_version_path)
 
     def _build_custom_base_url_to_api_version(
         self, paths_to_versions: List[Path]
@@ -317,7 +352,7 @@ def process(self) -> bool:
 
         # Detect if this client is using an operation mixin (Network)
         # Operation mixins are available since Autorest.Python 4.x
-        mixin_operations = self._build_operation_mixin_meta(paths_to_versions)
+        mixin_operations = self._build_operation_mixin_meta(paths_to_versions, last_api_version)
 
         # get client name from default api version
         path_to_default_version = Path()
diff --git a/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/_microsoft_azure_test_url.py b/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/_microsoft_azure_test_url.py
index ed1fe35b9c8..f04614ffb4b 100644
--- a/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/_microsoft_azure_test_url.py
+++ b/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/_microsoft_azure_test_url.py
@@ -44,7 +44,7 @@ def __init__(
     ):
         # type: (...) -> None
         if not base_url:
-            base_url = 'https://management.azure.com'
+            base_url = 'http://localhost:3000'
         self._config = MicrosoftAzureTestUrlConfiguration(credential, subscription_id, **kwargs)
         self._client = ARMPipelineClient(base_url=base_url, config=self._config, **kwargs)
 
diff --git a/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/aio/_microsoft_azure_test_url_async.py b/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/aio/_microsoft_azure_test_url_async.py
index d43ea134833..02496effde8 100644
--- a/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/aio/_microsoft_azure_test_url_async.py
+++ b/test/azure/Expected/AcceptanceTests/SubscriptionIdApiVersion/subscriptionidapiversion/aio/_microsoft_azure_test_url_async.py
@@ -41,7 +41,7 @@ def __init__(
         **kwargs: Any
     ) -> None:
         if not base_url:
-            base_url = 'https://management.azure.com'
+            base_url = 'http://localhost:3000'
         self._config = MicrosoftAzureTestUrlConfiguration(credential, subscription_id, **kwargs)
         self._client = AsyncARMPipelineClient(base_url=base_url, config=self._config, **kwargs)