diff --git a/pkg-py/src/querychat/_querychat.py b/pkg-py/src/querychat/_querychat.py
index 3e4f59f5..52136587 100644
--- a/pkg-py/src/querychat/_querychat.py
+++ b/pkg-py/src/querychat/_querychat.py
@@ -40,6 +40,7 @@ def __init__(
         greeting: Optional[str | Path] = None,
         client: Optional[str | chatlas.Chat] = None,
         data_description: Optional[str | Path] = None,
+        categorical_threshold: int = 10,
         extra_instructions: Optional[str | Path] = None,
         prompt_template: Optional[str | Path] = None,
     ):
@@ -79,6 +80,9 @@ def __init__(
             Description of the data in plain text or Markdown. If a pathlib.Path
             object is passed, querychat will read the contents of the path into a
             string with `.read_text()`.
+        categorical_threshold
+            Threshold for determining if a column is categorical based on number of
+            unique values.
         extra_instructions
             Additional instructions for the chat model. If a pathlib.Path object is
             passed, querychat will read the contents of the path into a string with
@@ -104,7 +108,7 @@ def __init__(
         ```
 
         """
-        self.data_source = normalize_data_source(data_source, table_name)
+        self._data_source = normalize_data_source(data_source, table_name)
 
         # Validate table name (must begin with letter, contain only letters, numbers, underscores)
         if not re.match(r"^[a-zA-Z][a-zA-Z0-9_]*$", table_name):
@@ -114,8 +118,6 @@ def __init__(
 
         self.id = id or table_name
 
-        self.client = normalize_client(client)
-
         if greeting is None:
             print(
                 "Warning: No greeting provided; the LLM will be invoked at conversation start to generate one. "
@@ -126,13 +128,20 @@ def __init__(
 
         self.greeting = greeting.read_text() if isinstance(greeting, Path) else greeting
 
-        self.system_prompt = get_system_prompt(
-            self.data_source,
+        prompt = get_system_prompt(
+            self._data_source,
             data_description=data_description,
             extra_instructions=extra_instructions,
+            categorical_threshold=categorical_threshold,
             prompt_template=prompt_template,
         )
 
+        # Fork and empty chat now so the per-session forks are fast
+        client = normalize_client(client)
+        self._client = copy.deepcopy(client)
+        self._client.set_turns([])
+        self._client.system_prompt = prompt
+
         # Populated when ._server() gets called (in an active session)
         self._server_values: ModServerResult | None = None
 
@@ -160,7 +169,7 @@ def app(
 
         """
         enable_bookmarking = bookmark_store != "disable"
-        table_name = self.data_source.table_name
+        table_name = self._data_source.table_name
 
         def app_ui(request):
             return ui.page_sidebar(
@@ -303,10 +312,9 @@ def _server(self, *, enable_bookmarking: bool = False) -> None:
         # Call the server module
         self._server_values = mod_server(
             self.id,
-            data_source=self.data_source,
-            system_prompt=self.system_prompt,
+            data_source=self._data_source,
             greeting=self.greeting,
-            client=self.client,
+            client=self._client,
             enable_bookmarking=enable_bookmarking,
         )
 
@@ -416,7 +424,7 @@ def title(self, value: Optional[str] = None) -> str | None | bool:
         else:
             return vals.title.set(value)
 
-    def generate_greeting(self, *, echo: Literal["none", "text"] = "none"):
+    def generate_greeting(self, *, echo: Literal["none", "output"] = "none"):
         """
         Generate a welcome greeting for the chat.
 
@@ -428,7 +436,7 @@ def generate_greeting(self, *, echo: Literal["none", "text"] = "none"):
         Parameters
         ----------
         echo
-            If `echo = "text"`, prints the greeting to standard output. If
+            If `echo = "output"`, prints the greeting to standard output. If
             `echo = "none"` (default), does not print anything.
 
         Returns
@@ -437,97 +445,39 @@ def generate_greeting(self, *, echo: Literal["none", "text"] = "none"):
             The greeting string (in Markdown format).
 
         """
-        client = copy.deepcopy(self.client)
-        client.system_prompt = self.system_prompt
+        client = copy.deepcopy(self._client)
         client.set_turns([])
         prompt = "Please give me a friendly greeting. Include a few sample prompts in a two-level bulleted list."
         return str(client.chat(prompt, echo=echo))
 
-    def set_system_prompt(
-        self,
-        data_source: DataSource,
-        *,
-        data_description: Optional[str | Path] = None,
-        extra_instructions: Optional[str | Path] = None,
-        categorical_threshold: int = 10,
-        prompt_template: Optional[str | Path] = None,
-    ) -> None:
-        """
-        Customize the system prompt.
-
-        Control the logic behind how the system prompt is generated based on the
-        data source's schema and optional additional context and instructions.
-
-        Note
-        ----
-        This method is for parametrized system prompt generation only. To set a
-        fully custom system prompt string, set the `system_prompt` attribute
-        directly.
-
-        Parameters
-        ----------
-        data_source
-            A data source to generate schema information from
-        data_description
-            Optional description of the data, in plain text or Markdown format
-        extra_instructions
-            Optional additional instructions for the chat model, in plain text or
-            Markdown format
-        categorical_threshold
-            Threshold for determining if a column is categorical based on number of
-            unique values
-        prompt_template
-            Optional `Path` to or string of a custom prompt template. If not provided, the default
-            querychat template will be used.
-
-        """
-        self.system_prompt = get_system_prompt(
-            data_source,
-            data_description=data_description,
-            extra_instructions=extra_instructions,
-            categorical_threshold=categorical_threshold,
-            prompt_template=prompt_template,
-        )
-
-    def set_data_source(
-        self, data_source: IntoFrame | sqlalchemy.Engine | DataSource, table_name: str
-    ) -> None:
+    @property
+    def client(self):
         """
-        Set a new data source for the QueryChat object.
-
-        Parameters
-        ----------
-        data_source
-            The new data source to use.
-        table_name
-            If a data_source is a data frame, a name to use to refer to the table
+        Get the (session-specific) chat client.
 
         Returns
         -------
         :
-            None
+            The current chat client.
 
         """
-        self.data_source = normalize_data_source(data_source, table_name)
+        vals = self._server_values
+        if vals is None:
+            raise RuntimeError("Must call .server() before accessing .client")
+        return vals.client
 
-    def set_client(self, client: str | chatlas.Chat) -> None:
+    @property
+    def data_source(self):
         """
-        Set a new chat client for the QueryChat object.
-
-        Parameters
-        ----------
-        client
-            A `chatlas.Chat` object or a string to be passed to
-            `chatlas.ChatAuto()` describing the model to use (e.g.
-            `"openai/gpt-4.1"`).
+        Get the current data source.
 
         Returns
         -------
         :
-            None
+            The current data source.
 
         """
-        self.client = normalize_client(client)
+        return self._data_source
 
 
 class QueryChat(QueryChatBase):
diff --git a/pkg-py/src/querychat/_querychat_module.py b/pkg-py/src/querychat/_querychat_module.py
index 6153a5b8..4fd83570 100644
--- a/pkg-py/src/querychat/_querychat_module.py
+++ b/pkg-py/src/querychat/_querychat_module.py
@@ -58,7 +58,6 @@ def mod_server(
     session: Session,
     *,
     data_source: DataSource,
-    system_prompt: str,
     greeting: str | None,
     client: chatlas.Chat,
     enable_bookmarking: bool,
@@ -70,8 +69,6 @@ def mod_server(
 
     # Set up the chat object for this session
     chat = copy.deepcopy(client)
-    chat.set_turns([])
-    chat.system_prompt = system_prompt
 
     # Create the tool functions
     update_dashboard_tool = tool_update_dashboard(data_source, sql, title)
diff --git a/pkg-py/tests/test_init_with_pandas.py b/pkg-py/tests/test_init_with_pandas.py
index 3f94b639..7c182639 100644
--- a/pkg-py/tests/test_init_with_pandas.py
+++ b/pkg-py/tests/test_init_with_pandas.py
@@ -39,10 +39,6 @@ def test_init_with_pandas_dataframe():
 
     # Verify the result is properly configured
     assert qc is not None
-    assert hasattr(qc, "data_source")
-    assert hasattr(qc, "system_prompt")
-    assert hasattr(qc, "greeting")
-    assert hasattr(qc, "client")
 
 
 def test_init_with_narwhals_dataframe():
@@ -66,8 +62,6 @@ def test_init_with_narwhals_dataframe():
 
     # Verify the result is correctly configured
     assert qc is not None
-    assert hasattr(qc, "data_source")
-    assert hasattr(qc, "system_prompt")
 
 
 def test_init_with_narwhals_lazyframe_direct_query():
diff --git a/pkg-py/tests/test_querychat.py b/pkg-py/tests/test_querychat.py
index b8267b46..5ffce90b 100644
--- a/pkg-py/tests/test_querychat.py
+++ b/pkg-py/tests/test_querychat.py
@@ -39,10 +39,6 @@ def test_querychat_init(sample_df):
 
     # Verify basic attributes are set
     assert qc is not None
-    assert hasattr(qc, "data_source")
-    assert hasattr(qc, "system_prompt")
-    assert hasattr(qc, "greeting")
-    assert hasattr(qc, "client")
     assert qc.id == "test_table"
 
     # Even without server initialization, we should be able to query the data source
@@ -66,31 +62,6 @@ def test_querychat_custom_id(sample_df):
     assert qc.id == "custom_id"
 
 
-def test_querychat_set_methods(sample_df):
-    """Test that setter methods work."""
-    qc = QueryChat(
-        data_source=sample_df,
-        table_name="test_table",
-        greeting="Hello!",
-    )
-
-    # Test set_system_prompt
-    qc.set_system_prompt(
-        qc.data_source,
-        data_description="A test dataset",
-    )
-    assert "test dataset" in qc.system_prompt.lower()
-
-    # Test set_data_source
-    new_df = pd.DataFrame({"x": [1, 2, 3]})
-    qc.set_data_source(new_df, "new_table")
-    assert qc.data_source is not None
-
-    # Test set_client
-    qc.set_client("openai/gpt-4o-mini")
-    assert qc.client is not None
-
-
 def test_querychat_core_reactive_access_before_server_raises(sample_df):
     """Test that accessing reactive properties before .server() raises error."""
     qc = QueryChat(