diff --git a/cli/src/commands/__tests__/command-args.test.ts b/cli/src/commands/__tests__/command-args.test.ts
index c755c953ae..47b8a1d691 100644
--- a/cli/src/commands/__tests__/command-args.test.ts
+++ b/cli/src/commands/__tests__/command-args.test.ts
@@ -164,7 +164,7 @@ describe('command factory pattern', () => {
     })
 
     test('expected commands ignore args', () => {
-      const expectedNoArgs = ['login', 'logout', 'exit', 'usage', 'init']
+      const expectedNoArgs = ['login', 'logout', 'exit', 'usage', 'init', 'compact']
       for (const name of expectedNoArgs) {
         const cmd = COMMAND_REGISTRY.find((c) => c.name === name)
         expect(cmd, `Command ${name} should exist`).toBeDefined()
diff --git a/cli/src/commands/__tests__/compact-command.test.ts b/cli/src/commands/__tests__/compact-command.test.ts
new file mode 100644
index 0000000000..449147836a
--- /dev/null
+++ b/cli/src/commands/__tests__/compact-command.test.ts
@@ -0,0 +1,182 @@
+import { beforeEach, describe, expect, mock, test } from 'bun:test'
+
+import { useChatStore } from '../../state/chat-store'
+import { findCommand } from '../command-registry'
+import { handleCompactCommand } from '../compact'
+import { parseCommandInput } from '../router-utils'
+import { getUserMessage } from '../../utils/message-history'
+
+import type { RouterParams } from '../command-registry'
+import type { ChatMessage } from '../../types/chat'
+
+const createMockParams = (
+  overrides: Partial<RouterParams> = {},
+): RouterParams =>
+  ({
+    agentMode: 'DEFAULT',
+    inputRef: { current: { focus: mock(() => {}) } as never },
+    inputValue: '/compact',
+    isChainInProgressRef: { current: false },
+    isStreaming: false,
+    logoutMutation: {} as RouterParams['logoutMutation'],
+    streamMessageIdRef: { current: null },
+    addToQueue: mock(() => {}),
+    hasQueuedMessages: () => false,
+    clearMessages: mock(() => {}),
+    saveToHistory: mock(() => {}),
+    scrollToLatest: mock(() => {}),
+    sendMessage: mock(async () => {}),
+    setCanProcessQueue: mock(() => {}),
+    setInputFocused: mock(() => {}),
+    setInputValue: mock(() => {}),
+    setIsAuthenticated: mock(() => {}),
+    setMessages: mock(() => {}),
+    setUser: mock(() => {}),
+    ...overrides,
+  }) as RouterParams
+
+describe('handleCompactCommand', () => {
+  beforeEach(() => {
+    useChatStore.setState({
+      messages: [],
+      pendingAttachments: [],
+    })
+  })
+
+  test('bails out early with system message when conversation is empty', async () => {
+    const params = createMockParams({ inputValue: '/compact' })
+
+    await handleCompactCommand(params)
+
+    expect(params.saveToHistory).toHaveBeenCalledWith('/compact')
+    expect(params.setInputValue).toHaveBeenCalledWith({
+      text: '',
+      cursorPosition: 0,
+      lastEditDueToNav: false,
+    })
+    expect(params.setMessages).toHaveBeenCalledTimes(1)
+
+    // Inspect the system message added
+    const updater = (params.setMessages as ReturnType<typeof mock>).mock
+      .calls[0][0] as (prev: ChatMessage[]) => ChatMessage[]
+    const resultingMessages = updater([])
+    expect(resultingMessages.length).toBe(1)
+    expect(resultingMessages[0].content).toContain('Nothing to compact')
+    expect(resultingMessages[0].id).toStartWith('sys-')
+
+    // Must NOT call sendMessage or addToQueue
+    expect(params.sendMessage).not.toHaveBeenCalled()
+    expect(params.addToQueue).not.toHaveBeenCalled()
+  })
+
+  test('dispatches /compact to sendMessage when idle and messages exist', async () => {
+    useChatStore.setState({
+      messages: [getUserMessage('Hello, world!')],
+    })
+
+    const params = createMockParams({
+      inputValue: '/compact',
+      agentMode: 'DEFAULT',
+    })
+
+    await handleCompactCommand(params)
+
+    expect(params.saveToHistory).toHaveBeenCalledWith('/compact')
+    expect(params.setInputValue).toHaveBeenCalledWith({
+      text: '',
+      cursorPosition: 0,
+      lastEditDueToNav: false,
+    })
+    expect(params.addToQueue).not.toHaveBeenCalled()
+    expect(params.sendMessage).toHaveBeenCalledWith({
+      content: '/compact',
+      agentMode: 'DEFAULT',
+    })
+  })
+
+  test('queues /compact when streaming is in progress', async () => {
+    useChatStore.setState({
+      messages: [getUserMessage('Running code')],
+    })
+
+    const params = createMockParams({
+      inputValue: '/compact',
+      isStreaming: true,
+    })
+
+    await handleCompactCommand(params)
+
+    expect(params.saveToHistory).toHaveBeenCalledWith('/compact')
+    expect(params.addToQueue).toHaveBeenCalledWith('/compact', [])
+    expect(params.setInputFocused).toHaveBeenCalledWith(true)
+    expect(params.sendMessage).not.toHaveBeenCalled()
+  })
+
+  test('queues /compact when chain is in progress', async () => {
+    useChatStore.setState({
+      messages: [getUserMessage('Running chain')],
+    })
+
+    const params = createMockParams({
+      inputValue: '/compact',
+      isChainInProgressRef: { current: true },
+    })
+
+    await handleCompactCommand(params)
+
+    expect(params.addToQueue).toHaveBeenCalledWith('/compact', [])
+    expect(params.sendMessage).not.toHaveBeenCalled()
+  })
+
+  test('queues /compact when streamMessageIdRef is active', async () => {
+    useChatStore.setState({
+      messages: [getUserMessage('Active stream')],
+    })
+
+    const params = createMockParams({
+      inputValue: '/compact',
+      streamMessageIdRef: { current: 'ai-msg-123' },
+    })
+
+    await handleCompactCommand(params)
+
+    expect(params.addToQueue).toHaveBeenCalledWith('/compact', [])
+    expect(params.sendMessage).not.toHaveBeenCalled()
+  })
+})
+
+describe('compact command registry and aliases', () => {
+  test('findCommand resolves compact by primary name', () => {
+    const cmd = findCommand('compact')
+    expect(cmd).toBeDefined()
+    expect(cmd?.name).toBe('compact')
+    expect(cmd?.aliases).toContain('summarize')
+    expect(cmd?.acceptsArgs).toBe(false)
+  })
+
+  test('findCommand resolves compact by summarize alias', () => {
+    const cmd = findCommand('summarize')
+    expect(cmd).toBeDefined()
+    expect(cmd?.name).toBe('compact')
+  })
+
+  test('parseCommandInput supports /compact and slashless compact', () => {
+    expect(parseCommandInput('/compact')).toEqual({
+      command: 'compact',
+      args: '',
+      implicitCommand: false,
+    })
+
+    expect(parseCommandInput('compact')).toEqual({
+      command: 'compact',
+      args: '',
+      implicitCommand: true,
+    })
+
+    expect(parseCommandInput('/summarize')).toEqual({
+      command: 'summarize',
+      args: '',
+      implicitCommand: false,
+    })
+  })
+})
diff --git a/cli/src/commands/command-registry.ts b/cli/src/commands/command-registry.ts
index 9c381796fc..2e5122793b 100644
--- a/cli/src/commands/command-registry.ts
+++ b/cli/src/commands/command-registry.ts
@@ -9,6 +9,7 @@ import {
   handleProposalReport,
   handleProposalsOff,
 } from './ads'
+import { handleCompactCommand } from './compact'
 import { handleCopyConversationCommand } from './copy-conversation'
 import { handleExportConversationCommand } from './export-conversation'
 import { handleHelpCommand } from './help'
@@ -313,6 +314,13 @@ const ALL_COMMANDS: CommandDefinition[] = [
       await handleExportConversationCommand(params, args)
     },
   }),
+  defineCommand({
+    name: 'compact',
+    aliases: ['summarize'],
+    handler: async (params) => {
+      await handleCompactCommand(params)
+    },
+  }),
   defineCommandWithArgs({
     name: 'feedback',
     aliases: ['bug', 'report'],
diff --git a/cli/src/commands/compact.ts b/cli/src/commands/compact.ts
new file mode 100644
index 0000000000..d3a95059e7
--- /dev/null
+++ b/cli/src/commands/compact.ts
@@ -0,0 +1,50 @@
+import { useChatStore } from '../state/chat-store'
+import { getSystemMessage } from '../utils/message-history'
+import { capturePendingAttachments } from '../utils/pending-attachments'
+
+import type { RouterParams } from './command-registry'
+
+/**
+ * Handle the `/compact` (and `/summarize`) command.
+ *
+ * Bails out early with a system message when the conversation is empty,
+ * queues the command if a stream or chain is actively running,
+ * or dispatches `/compact` to the agent runtime to summarize and compact history.
+ */
+export async function handleCompactCommand(
+  params: RouterParams,
+): Promise<void> {
+  const trimmed = params.inputValue.trim()
+  params.saveToHistory(trimmed)
+  params.setInputValue({ text: '', cursorPosition: 0, lastEditDueToNav: false })
+
+  const messages = useChatStore.getState().messages
+  if (messages.length === 0) {
+    params.setMessages((prev) => [
+      ...prev,
+      getSystemMessage('Nothing to compact — the conversation is empty.'),
+    ])
+    return
+  }
+
+  // Check streaming/queue state
+  if (
+    params.isStreaming ||
+    params.streamMessageIdRef.current ||
+    params.isChainInProgressRef.current
+  ) {
+    const pendingAttachments = capturePendingAttachments()
+    params.addToQueue('/compact', pendingAttachments)
+    params.setInputFocused(true)
+    params.inputRef.current?.focus()
+    return
+  }
+
+  params.sendMessage({
+    content: '/compact',
+    agentMode: params.agentMode,
+  })
+  setTimeout(() => {
+    params.scrollToLatest()
+  }, 0)
+}
diff --git a/cli/src/data/slash-commands.ts b/cli/src/data/slash-commands.ts
index c9a1321c11..37d1eeca7d 100644
--- a/cli/src/data/slash-commands.ts
+++ b/cli/src/data/slash-commands.ts
@@ -146,6 +146,13 @@ const ALL_SLASH_COMMANDS: SlashCommand[] = [
     description: 'Write the full conversation to a file (.md, or .json for raw messages)',
     aliases: ['export-chat'],
   },
+  {
+    id: 'compact',
+    label: 'compact',
+    description: 'Compact conversation history to reclaim context space',
+    aliases: ['summarize'],
+    implicitCommand: true,
+  },
   {
     id: 'agent:gpt-5',
     label: 'agent:gpt-5',