diff --git a/src/cli/App.tsx b/src/cli/App.tsx
index e786646..4cafc03 100644
--- a/src/cli/App.tsx
+++ b/src/cli/App.tsx
@@ -142,6 +142,7 @@ import { ApprovalSwitch } from "./components/ApprovalSwitch";
 import { AssistantMessage } from "./components/AssistantMessageRich";
 import { BashCommandMessage } from "./components/BashCommandMessage";
 import { CommandMessage } from "./components/CommandMessage";
+import { CompactionSelector } from "./components/CompactionSelector";
 import { ConversationSelector } from "./components/ConversationSelector";
 import { colors } from "./components/colors";
 // EnterPlanModeDialog removed - now using InlineEnterPlanModeApproval
@@ -1352,6 +1353,7 @@ export default function App({
   type ActiveOverlay =
     | "model"
     | "sleeptime"
+    | "compaction"
     | "toolset"
     | "system"
     | "agent"
@@ -1423,6 +1425,11 @@ export default function App({
         settings: ReflectionSettings;
         commandId?: string;
       }
+    | {
+        type: "set_compaction";
+        mode: string;
+        commandId?: string;
+      }
     | {
         type: "switch_conversation";
         conversationId: string;
@@ -6808,6 +6815,18 @@ export default function App({
           return { submitted: true };
         }
 
+        // Special handling for /compaction command - opens compaction mode settings
+        if (trimmed === "/compaction") {
+          startOverlayCommand(
+            "compaction",
+            "/compaction",
+            "Opening compaction settings...",
+            "Compaction settings dismissed",
+          );
+          setActiveOverlay("compaction");
+          return { submitted: true };
+        }
+
         // Special handling for /toolset command - opens selector
         if (trimmed === "/toolset") {
           startOverlayCommand(
@@ -11213,6 +11232,78 @@ ${SYSTEM_REMINDER_CLOSE}
     ],
   );
 
+  const handleCompactionModeSelect = useCallback(
+    async (mode: string, commandId?: string | null) => {
+      const overlayCommand = commandId
+        ? commandRunner.getHandle(commandId, "/compaction")
+        : consumeOverlayCommand("compaction");
+
+      if (isAgentBusy()) {
+        setActiveOverlay(null);
+        const cmd =
+          overlayCommand ??
+          commandRunner.start(
+            "/compaction",
+            "Compaction settings update queued – will apply after current task completes",
+          );
+        cmd.update({
+          output:
+            "Compaction settings update queued – will apply after current task completes",
+          phase: "running",
+        });
+        setQueuedOverlayAction({
+          type: "set_compaction",
+          mode,
+          commandId: cmd.id,
+        });
+        return;
+      }
+
+      await withCommandLock(async () => {
+        const cmd =
+          overlayCommand ??
+          commandRunner.start("/compaction", "Saving compaction settings...");
+        cmd.update({
+          output: "Saving compaction settings...",
+          phase: "running",
+        });
+
+        try {
+          const client = await getClient();
+          // Spread existing compaction_settings to preserve model/other fields,
+          // only override the mode. If no existing settings, use empty model
+          // string which tells the backend to use its default lightweight model.
+          const existing = agentState?.compaction_settings;
+
+          await client.agents.update(agentId, {
+            compaction_settings: {
+              model: existing?.model ?? "",
+              ...existing,
+              mode: mode as
+                | "all"
+                | "sliding_window"
+                | "self_compact_all"
+                | "self_compact_sliding_window",
+            },
+          });
+
+          cmd.finish(`Updated compaction mode to: ${mode}`, true);
+        } catch (error) {
+          const errorDetails = formatErrorDetails(error, agentId);
+          cmd.fail(`Failed to save compaction settings: ${errorDetails}`);
+        }
+      });
+    },
+    [
+      agentId,
+      commandRunner,
+      consumeOverlayCommand,
+      isAgentBusy,
+      withCommandLock,
+      agentState?.compaction_settings,
+    ],
+  );
+
   const handleToolsetSelect = useCallback(
     async (toolsetId: ToolsetPreference, commandId?: string | null) => {
       const overlayCommand = commandId
@@ -11346,6 +11437,8 @@ ${SYSTEM_REMINDER_CLOSE}
         handleModelSelect(action.modelId, action.commandId);
       } else if (action.type === "set_sleeptime") {
         handleSleeptimeModeSelect(action.settings, action.commandId);
+      } else if (action.type === "set_compaction") {
+        handleCompactionModeSelect(action.mode, action.commandId);
       } else if (action.type === "switch_conversation") {
         const cmd = action.commandId
           ? commandRunner.getHandle(action.commandId, "/resume")
@@ -11426,6 +11519,7 @@ ${SYSTEM_REMINDER_CLOSE}
     handleAgentSelect,
     handleModelSelect,
     handleSleeptimeModeSelect,
+    handleCompactionModeSelect,
     handleToolsetSelect,
     handleSystemPromptSelect,
     agentId,
@@ -12840,6 +12934,14 @@ If using apply_patch, use this exact relative patch path: ${applyPatchRelativePa
               />
             )}
 
+            {activeOverlay === "compaction" && (
+              <CompactionSelector
+                initialMode={agentState?.compaction_settings?.mode}
+                onSave={handleCompactionModeSelect}
+                onCancel={closeOverlay}
+              />
+            )}
+
             {/* GitHub App Installer - setup Letta Code GitHub Action */}
             {activeOverlay === "install-github-app" && (
               <InstallGithubAppFlow
diff --git a/src/cli/commands/registry.ts b/src/cli/commands/registry.ts
index a7235e9..40b22d7 100644
--- a/src/cli/commands/registry.ts
+++ b/src/cli/commands/registry.ts
@@ -92,6 +92,15 @@ export const commands: Record<string, Command> = {
       return "Opening sleeptime settings...";
     },
   },
+  "/compaction": {
+    desc: "Configure compaction mode settings",
+    order: 15.6,
+    noArgs: true,
+    handler: () => {
+      // Handled specially in App.tsx to open compaction settings
+      return "Opening compaction settings...";
+    },
+  },
   "/memfs": {
     desc: "Manage filesystem-backed memory (/memfs [enable|disable|sync|reset])",
     args: "[enable|disable|sync|reset]",
diff --git a/src/cli/components/CompactionSelector.tsx b/src/cli/components/CompactionSelector.tsx
new file mode 100644
index 0000000..0ddb15b
--- /dev/null
+++ b/src/cli/components/CompactionSelector.tsx
@@ -0,0 +1,128 @@
+import { Box, useInput } from "ink";
+import { useMemo, useState } from "react";
+import { useTerminalWidth } from "../hooks/useTerminalWidth";
+import { colors } from "./colors";
+import { Text } from "./Text";
+
+const SOLID_LINE = "─";
+
+type CompactionMode =
+  | "all"
+  | "sliding_window"
+  | "self_compact_all"
+  | "self_compact_sliding_window";
+const MODE_OPTIONS: CompactionMode[] = [
+  "all",
+  "sliding_window",
+  "self_compact_all",
+  "self_compact_sliding_window",
+];
+const MODE_LABELS: Record<CompactionMode, string> = {
+  all: "All",
+  sliding_window: "Sliding Window",
+  self_compact_all: "Self Compact All",
+  self_compact_sliding_window: "Self Compact Sliding Window",
+};
+
+function cycleOption<T extends string>(
+  options: readonly T[],
+  current: T,
+  direction: -1 | 1,
+): T {
+  if (options.length === 0) {
+    return current;
+  }
+  const currentIndex = options.indexOf(current);
+  const safeIndex = currentIndex >= 0 ? currentIndex : 0;
+  const nextIndex = (safeIndex + direction + options.length) % options.length;
+  return options[nextIndex] ?? current;
+}
+
+interface CompactionSelectorProps {
+  initialMode: string | null | undefined;
+  onSave: (mode: CompactionMode) => void;
+  onCancel: () => void;
+}
+
+export function CompactionSelector({
+  initialMode,
+  onSave,
+  onCancel,
+}: CompactionSelectorProps) {
+  const terminalWidth = useTerminalWidth();
+  const solidLine = SOLID_LINE.repeat(Math.max(terminalWidth, 10));
+
+  const parsedInitialMode = useMemo((): CompactionMode => {
+    if (
+      initialMode === "all" ||
+      initialMode === "sliding_window" ||
+      initialMode === "self_compact_all" ||
+      initialMode === "self_compact_sliding_window"
+    ) {
+      return initialMode as CompactionMode;
+    }
+    return "sliding_window";
+  }, [initialMode]);
+
+  const [mode, setMode] = useState<CompactionMode>(parsedInitialMode);
+
+  useInput((input, key) => {
+    if (key.ctrl && input === "c") {
+      onCancel();
+      return;
+    }
+
+    if (key.escape) {
+      onCancel();
+      return;
+    }
+
+    if (key.return) {
+      onSave(mode);
+      return;
+    }
+
+    if (key.leftArrow || key.rightArrow || key.tab) {
+      const direction: -1 | 1 = key.leftArrow ? -1 : 1;
+      setMode((prev) => cycleOption(MODE_OPTIONS, prev, direction));
+    }
+  });
+
+  return (
+    <Box flexDirection="column">
+      <Text dimColor>{"> /compaction"}</Text>
+      <Text dimColor>{solidLine}</Text>
+
+      <Box height={1} />
+
+      <Text bold color={colors.selector.title}>
+        Configure compaction mode
+      </Text>
+
+      <Box height={1} />
+
+      <Box flexDirection="row">
+        <Text>{"> "}</Text>
+        <Text bold>Mode:</Text>
+        <Text>{"   "}</Text>
+        {MODE_OPTIONS.map((opt) => (
+          <Box key={opt} flexDirection="row">
+            <Text
+              backgroundColor={
+                mode === opt ? colors.selector.itemHighlighted : undefined
+              }
+              color={mode === opt ? "black" : undefined}
+              bold={mode === opt}
+            >
+              {` ${MODE_LABELS[opt]} `}
+            </Text>
+            <Text> </Text>
+          </Box>
+        ))}
+      </Box>
+
+      <Box height={1} />
+      <Text dimColor>{"  Enter to save · ←→/Tab options · Esc cancel"}</Text>
+    </Box>
+  );
+}