diff --git a/google/cloud/firestore_v1/async_aggregation.py b/google/cloud/firestore_v1/async_aggregation.py
index c39b50c5e4..191404a73a 100644
--- a/google/cloud/firestore_v1/async_aggregation.py
+++ b/google/cloud/firestore_v1/async_aggregation.py
@@ -23,9 +23,9 @@
 from google.api_core import gapic_v1
 from google.api_core import retry_async as retries
 
-from typing import List, Union, AsyncGenerator
-
+from typing import List, Union, AsyncGenerator, Optional
 
+from google.cloud.firestore_v1.async_transaction import AsyncTransaction
 from google.cloud.firestore_v1.base_aggregation import (
     AggregationResult,
     _query_response_to_result,
@@ -78,7 +78,7 @@ async def get(
 
     async def stream(
         self,
-        transaction=None,
+        transaction: Optional[AsyncTransaction] = None,
         retry: Union[
             retries.AsyncRetry, None, gapic_v1.method._MethodDefault
         ] = gapic_v1.method.DEFAULT,
diff --git a/google/cloud/firestore_v1/async_batch.py b/google/cloud/firestore_v1/async_batch.py
index 84b45fa094..d0eab88479 100644
--- a/google/cloud/firestore_v1/async_batch.py
+++ b/google/cloud/firestore_v1/async_batch.py
@@ -19,6 +19,7 @@
 from google.api_core import retry_async as retries
 
 from google.cloud.firestore_v1.base_batch import BaseWriteBatch
+from typing import Optional
 
 
 class AsyncWriteBatch(BaseWriteBatch):
@@ -39,7 +40,7 @@ def __init__(self, client) -> None:
     async def commit(
         self,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> list:
         """Commit the changes accumulated in this batch.
 
diff --git a/google/cloud/firestore_v1/async_client.py b/google/cloud/firestore_v1/async_client.py
index 20541c3770..305665df48 100644
--- a/google/cloud/firestore_v1/async_client.py
+++ b/google/cloud/firestore_v1/async_client.py
@@ -227,9 +227,9 @@ async def get_all(
         self,
         references: List[AsyncDocumentReference],
         field_paths: Iterable[str] = None,
-        transaction=None,
+        transaction: Optional[AsyncTransaction] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator[DocumentSnapshot, Any]:
         """Retrieve a batch of documents.
 
@@ -285,7 +285,7 @@ async def get_all(
     async def collections(
         self,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator[AsyncCollectionReference, Any]:
         """List top-level collections of the client's database.
 
diff --git a/google/cloud/firestore_v1/async_collection.py b/google/cloud/firestore_v1/async_collection.py
index 093117d40b..5255e10155 100644
--- a/google/cloud/firestore_v1/async_collection.py
+++ b/google/cloud/firestore_v1/async_collection.py
@@ -22,14 +22,12 @@
     _item_to_document_ref,
 )
 from google.cloud.firestore_v1 import async_query, async_document, async_aggregation
+from google.cloud.firestore_v1.async_transaction import AsyncTransaction
 
 from google.cloud.firestore_v1.document import DocumentReference
 
 from typing import AsyncIterator
-from typing import Any, AsyncGenerator, Tuple
-
-# Types needed only for Type Hints
-from google.cloud.firestore_v1.transaction import Transaction
+from typing import Any, AsyncGenerator, Tuple, Optional
 
 
 class AsyncCollectionReference(BaseCollectionReference[async_query.AsyncQuery]):
@@ -84,9 +82,9 @@ async def _chunkify(self, chunk_size: int):
     async def add(
         self,
         document_data: dict,
-        document_id: str = None,
+        document_id: Optional[str] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> Tuple[Any, Any]:
         """Create a document in the Firestore database with the provided data.
 
@@ -125,7 +123,7 @@ async def add(
         return write_result.update_time, document_ref
 
     def document(
-        self, document_id: str = None
+        self, document_id: Optional[str] = None
     ) -> async_document.AsyncDocumentReference:
         """Create a sub-document underneath the current collection.
 
@@ -143,9 +141,9 @@ def document(
 
     async def list_documents(
         self,
-        page_size: int = None,
+        page_size: Optional[int] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator[DocumentReference, None]:
         """List all subdocuments of the current collection.
 
@@ -176,9 +174,9 @@ async def list_documents(
 
     async def get(
         self,
-        transaction: Transaction = None,
+        transaction: Optional[AsyncTransaction] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> list:
         """Read the documents in this collection.
 
@@ -207,9 +205,9 @@ async def get(
 
     async def stream(
         self,
-        transaction: Transaction = None,
+        transaction: Optional[AsyncTransaction] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncIterator[async_document.DocumentSnapshot]:
         """Read the documents in this collection.
 
diff --git a/google/cloud/firestore_v1/async_document.py b/google/cloud/firestore_v1/async_document.py
index 75250d0b4c..a110b78c66 100644
--- a/google/cloud/firestore_v1/async_document.py
+++ b/google/cloud/firestore_v1/async_document.py
@@ -26,9 +26,10 @@
     _first_write_result,
 )
 from google.cloud.firestore_v1 import _helpers
+from google.cloud.firestore_v1.async_transaction import AsyncTransaction
 from google.cloud.firestore_v1.types import write
 from google.protobuf.timestamp_pb2 import Timestamp
-from typing import AsyncGenerator, Iterable
+from typing import AsyncGenerator, Iterable, Optional
 
 
 logger = logging.getLogger(__name__)
@@ -66,7 +67,7 @@ async def create(
         self,
         document_data: dict,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> write.WriteResult:
         """Create the current document in the Firestore database.
 
@@ -96,7 +97,7 @@ async def set(
         document_data: dict,
         merge: bool = False,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> write.WriteResult:
         """Replace the current document in the Firestore database.
 
@@ -134,9 +135,9 @@ async def set(
     async def update(
         self,
         field_updates: dict,
-        option: _helpers.WriteOption = None,
+        option: Optional[_helpers.WriteOption] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> write.WriteResult:
         """Update an existing document in the Firestore database.
 
@@ -291,9 +292,9 @@ async def update(
 
     async def delete(
         self,
-        option: _helpers.WriteOption = None,
+        option: Optional[_helpers.WriteOption] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> Timestamp:
         """Delete the current document in the Firestore database.
 
@@ -325,10 +326,10 @@ async def delete(
 
     async def get(
         self,
-        field_paths: Iterable[str] = None,
-        transaction=None,
+        field_paths: Optional[Iterable[str]] = None,
+        transaction: Optional[AsyncTransaction] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> DocumentSnapshot:
         """Retrieve a snapshot of the current document.
 
@@ -394,9 +395,9 @@ async def get(
 
     async def collections(
         self,
-        page_size: int = None,
+        page_size: Optional[int] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator:
         """List subcollections of the current document.
 
diff --git a/google/cloud/firestore_v1/async_query.py b/google/cloud/firestore_v1/async_query.py
index 8ee4012904..339274b27f 100644
--- a/google/cloud/firestore_v1/async_query.py
+++ b/google/cloud/firestore_v1/async_query.py
@@ -40,7 +40,7 @@
 
 if TYPE_CHECKING:  # pragma: NO COVER
     # Types needed only for Type Hints
-    from google.cloud.firestore_v1.transaction import Transaction
+    from google.cloud.firestore_v1.async_transaction import AsyncTransaction
     from google.cloud.firestore_v1.field_path import FieldPath
 
 
@@ -171,9 +171,9 @@ async def _chunkify(
 
     async def get(
         self,
-        transaction: Transaction = None,
+        transaction: Optional[AsyncTransaction] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> list:
         """Read the documents in the collection that match this query.
 
@@ -266,9 +266,9 @@ def avg(
 
     async def stream(
         self,
-        transaction=None,
+        transaction: Optional[AsyncTransaction] = None,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator[async_document.DocumentSnapshot, None]:
         """Read the documents in the collection that match this query.
 
diff --git a/google/cloud/firestore_v1/async_transaction.py b/google/cloud/firestore_v1/async_transaction.py
index 18a20b8e12..db5f541408 100644
--- a/google/cloud/firestore_v1/async_transaction.py
+++ b/google/cloud/firestore_v1/async_transaction.py
@@ -43,7 +43,7 @@
 from google.cloud.firestore_v1.async_document import AsyncDocumentReference
 from google.cloud.firestore_v1.async_document import DocumentSnapshot
 from google.cloud.firestore_v1.async_query import AsyncQuery
-from typing import Any, AsyncGenerator, Callable, Coroutine
+from typing import Any, AsyncGenerator, Callable, Coroutine, Optional
 
 # Types needed only for Type Hints
 from google.cloud.firestore_v1.client import Client
@@ -82,7 +82,7 @@ def _add_write_pbs(self, write_pbs: list) -> None:
 
         super(AsyncTransaction, self)._add_write_pbs(write_pbs)
 
-    async def _begin(self, retry_id: bytes = None) -> None:
+    async def _begin(self, retry_id: Optional[bytes] = None) -> None:
         """Begin the transaction.
 
         Args:
@@ -154,7 +154,7 @@ async def get_all(
         self,
         references: list,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator[DocumentSnapshot, Any]:
         """Retrieves multiple documents from Firestore.
 
@@ -177,7 +177,7 @@ async def get(
         self,
         ref_or_query,
         retry: retries.AsyncRetry = gapic_v1.method.DEFAULT,
-        timeout: float = None,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator[DocumentSnapshot, Any]:
         """
         Retrieve a document or a query result from the database.