diff --git a/cht/agent/base.py b/cht/agent/base.py
index 7335123..17be1f0 100644
--- a/cht/agent/base.py
+++ b/cht/agent/base.py
@@ -34,6 +34,7 @@ class SessionContext:
     mentioned_frames: list[FrameRef] = field(default_factory=list)
     transcript_segments: list[TranscriptRef] = field(default_factory=list)
     mentioned_transcripts: list[TranscriptRef] = field(default_factory=list)
+    history: list[tuple[str, str]] = field(default_factory=list)  # [(role, text), ...]
 
 
 class AgentProvider(ABC):
diff --git a/cht/agent/claude_sdk_provider.py b/cht/agent/claude_sdk_provider.py
index 6f8deac..ea5b42a 100644
--- a/cht/agent/claude_sdk_provider.py
+++ b/cht/agent/claude_sdk_provider.py
@@ -62,6 +62,12 @@ def _build_prompt(message: str, context: SessionContext) -> str:
             tm2, ts2 = divmod(int(t.end), 60)
             lines.append(f"  {t.id} [{tm1:02d}:{ts1:02d}-{tm2:02d}:{ts2:02d}] {t.text}")
 
+    if context.history:
+        lines.append("\nConversation history:")
+        for role, text in context.history:
+            prefix = "User" if role == "user" else "Assistant"
+            lines.append(f"  {prefix}: {text}")
+
     lines.append(f"\nUser message: {message}")
     return "\n".join(lines)
 
diff --git a/cht/agent/openai_compat_provider.py b/cht/agent/openai_compat_provider.py
index 20a045a..14eff50 100644
--- a/cht/agent/openai_compat_provider.py
+++ b/cht/agent/openai_compat_provider.py
@@ -118,12 +118,14 @@ class OpenAICompatProvider(AgentProvider):
             except Exception as e:
                 log.warning("Could not encode frame %s: %s", frame.id, e)
 
+        messages = [{"role": "system", "content": SYSTEM_PROMPT}]
+        for role, text in context.history:
+            messages.append({"role": role, "content": text})
+        messages.append({"role": "user", "content": content})
+
         stream = client.chat.completions.create(
             model=self._model,
-            messages=[
-                {"role": "system", "content": SYSTEM_PROMPT},
-                {"role": "user", "content": content},
-            ],
+            messages=messages,
             stream=True,
         )
         for chunk in stream:
diff --git a/cht/agent/runner.py b/cht/agent/runner.py
index e644f7e..e947be1 100644
--- a/cht/agent/runner.py
+++ b/cht/agent/runner.py
@@ -146,6 +146,8 @@ class AgentRunner:
 
     def __init__(self):
         self._provider: AgentProvider | None = None
+        self._history: list[tuple[str, str]] = []  # (role, text)
+        self.include_history = False  # toggled by UI
 
     def _get_provider(self) -> AgentProvider:
         if self._provider is None:
@@ -178,6 +180,9 @@ class AgentRunner:
     def model(self, value: str):
         self._get_provider().model = value
 
+    def clear_history(self):
+        self._history.clear()
+
     def send(
         self,
         message: str,
@@ -205,9 +210,14 @@ class AgentRunner:
                     mentioned_frames=mentioned_frames,
                     transcript_segments=transcript,
                     mentioned_transcripts=mentioned_transcripts,
+                    history=list(self._history) if self.include_history else [],
                 )
+                self._history.append(("user", message))
+                response_chunks = []
                 for chunk in provider.stream(message, context):
+                    response_chunks.append(chunk)
                     on_chunk(chunk)
+                self._history.append(("assistant", "".join(response_chunks)))
                 on_done(None)
             except Exception as e:
                 log.error("Agent error: %s", e)
diff --git a/cht/window.py b/cht/window.py
index 16c9c0b..5180d92 100644
--- a/cht/window.py
+++ b/cht/window.py
@@ -350,6 +350,7 @@ class ChtWindow(Adw.ApplicationWindow):
         self._waveform_engine.reset()
         self._waveform_widget.set_peaks(None, 0.05)
         self._transcriber.reset()
+        self._agent.clear_history()
         self._transcript_order.clear()
         self._transcript_rows.clear()
         self._transcript_texts.clear()
@@ -539,7 +540,7 @@ class ChtWindow(Adw.ApplicationWindow):
 
         clear_btn = Gtk.Button(label="Clear")
         clear_btn.add_css_class("flat")
-        clear_btn.connect("clicked", lambda b: self._agent_output_view.get_buffer().set_text(""))
+        clear_btn.connect("clicked", self._on_clear_agent_output)
         header.append(clear_btn)
 
         box.append(header)
@@ -600,6 +601,11 @@ class ChtWindow(Adw.ApplicationWindow):
         self._lang_dropdown.connect("notify::selected", self._on_lang_changed)
         actions_box.append(self._lang_dropdown)
 
+        self._history_toggle = Gtk.CheckButton(label="Chat")
+        self._history_toggle.set_tooltip_text("Include conversation history in prompts")
+        self._history_toggle.connect("toggled", lambda b: setattr(self._agent, "include_history", b.get_active()))
+        actions_box.append(self._history_toggle)
+
         outer.append(actions_box)
 
         # Text entry + send
@@ -775,7 +781,7 @@ class ChtWindow(Adw.ApplicationWindow):
                 self._send_message(msg)
                 return True
         elif keyval == Gdk.KEY_Delete:
-            self._agent_output_view.get_buffer().set_text("")
+            self._on_clear_agent_output(None)
             return True
         return False
 
@@ -989,6 +995,9 @@ class ChtWindow(Adw.ApplicationWindow):
             buf.apply_tag(tag, buf.get_iter_at_mark(mark), it)
             buf.delete_mark(mark)
 
+    def _on_clear_agent_output(self, _button):
+        self._agent_output_view.get_buffer().set_text("")
+
     def _on_lang_changed(self, dropdown, _pspec):
         idx = dropdown.get_selected()
         lang_names = list(LANGUAGES.keys())