diff --git a/slack_sdk/web/async_client.py b/slack_sdk/web/async_client.py
index 79293d8b9..0458b14c4 100644
--- a/slack_sdk/web/async_client.py
+++ b/slack_sdk/web/async_client.py
@@ -2131,7 +2131,7 @@ async def assistant_threads_setSuggestedPrompts(
         self,
         *,
         channel_id: str,
-        thread_ts: str,
+        thread_ts: Optional[str] = None,
         title: Optional[str] = None,
         prompts: List[Dict[str, str]],
         **kwargs,
@@ -2139,7 +2139,9 @@ async def assistant_threads_setSuggestedPrompts(
         """Set suggested prompts for the given assistant thread.
         https://docs.slack.dev/reference/methods/assistant.threads.setSuggestedPrompts
         """
-        kwargs.update({"channel_id": channel_id, "thread_ts": thread_ts, "prompts": prompts})
+        kwargs.update({"channel_id": channel_id, "prompts": prompts})
+        if thread_ts is not None:
+            kwargs.update({"thread_ts": thread_ts})
         if title is not None:
             kwargs.update({"title": title})
         return await self.api_call("assistant.threads.setSuggestedPrompts", json=kwargs)
diff --git a/slack_sdk/web/client.py b/slack_sdk/web/client.py
index 4c597c2df..967713b4e 100644
--- a/slack_sdk/web/client.py
+++ b/slack_sdk/web/client.py
@@ -2121,7 +2121,7 @@ def assistant_threads_setSuggestedPrompts(
         self,
         *,
         channel_id: str,
-        thread_ts: str,
+        thread_ts: Optional[str] = None,
         title: Optional[str] = None,
         prompts: List[Dict[str, str]],
         **kwargs,
@@ -2129,7 +2129,9 @@ def assistant_threads_setSuggestedPrompts(
         """Set suggested prompts for the given assistant thread.
         https://docs.slack.dev/reference/methods/assistant.threads.setSuggestedPrompts
         """
-        kwargs.update({"channel_id": channel_id, "thread_ts": thread_ts, "prompts": prompts})
+        kwargs.update({"channel_id": channel_id, "prompts": prompts})
+        if thread_ts is not None:
+            kwargs.update({"thread_ts": thread_ts})
         if title is not None:
             kwargs.update({"title": title})
         return self.api_call("assistant.threads.setSuggestedPrompts", json=kwargs)
diff --git a/slack_sdk/web/legacy_client.py b/slack_sdk/web/legacy_client.py
index afc4e4f64..ccbd09666 100644
--- a/slack_sdk/web/legacy_client.py
+++ b/slack_sdk/web/legacy_client.py
@@ -2132,7 +2132,7 @@ def assistant_threads_setSuggestedPrompts(
         self,
         *,
         channel_id: str,
-        thread_ts: str,
+        thread_ts: Optional[str] = None,
         title: Optional[str] = None,
         prompts: List[Dict[str, str]],
         **kwargs,
@@ -2140,7 +2140,9 @@ def assistant_threads_setSuggestedPrompts(
         """Set suggested prompts for the given assistant thread.
         https://docs.slack.dev/reference/methods/assistant.threads.setSuggestedPrompts
         """
-        kwargs.update({"channel_id": channel_id, "thread_ts": thread_ts, "prompts": prompts})
+        kwargs.update({"channel_id": channel_id, "prompts": prompts})
+        if thread_ts is not None:
+            kwargs.update({"thread_ts": thread_ts})
         if title is not None:
             kwargs.update({"title": title})
         return self.api_call("assistant.threads.setSuggestedPrompts", json=kwargs)