diff --git a/packages/app/src/components/agent-stream-view.tsx b/packages/app/src/components/agent-stream-view.tsx
index 8f7dfa4a5..7bd100e84 100644
--- a/packages/app/src/components/agent-stream-view.tsx
+++ b/packages/app/src/components/agent-stream-view.tsx
@@ -540,7 +540,13 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
             return <TodoListCard items={item.items} />;
 
           case "compaction":
-            return <CompactionMarker status={item.status} preTokens={item.preTokens} />;
+            return (
+              <CompactionMarker
+                status={item.status}
+                trigger={item.trigger}
+                preTokens={item.preTokens}
+              />
+            );
 
           default:
             return null;
diff --git a/packages/app/src/components/message-compaction-label.test.ts b/packages/app/src/components/message-compaction-label.test.ts
new file mode 100644
index 000000000..670ab8541
--- /dev/null
+++ b/packages/app/src/components/message-compaction-label.test.ts
@@ -0,0 +1,19 @@
+import { describe, expect, it } from "vitest";
+
+import { getCompactionMarkerLabel } from "./message-compaction-label";
+
+describe("getCompactionMarkerLabel", () => {
+  it("renders loading, automatic, manual, tokenized, and fallback labels", () => {
+    expect(getCompactionMarkerLabel({ status: "loading" })).toBe("Compacting...");
+    expect(getCompactionMarkerLabel({ status: "completed", trigger: "auto" })).toBe(
+      "Context automatically compacted",
+    );
+    expect(getCompactionMarkerLabel({ status: "completed", trigger: "manual" })).toBe(
+      "Context manually compacted",
+    );
+    expect(getCompactionMarkerLabel({ status: "completed", preTokens: 12_345 })).toBe(
+      "Context compacted (12K tokens)",
+    );
+    expect(getCompactionMarkerLabel({ status: "completed" })).toBe("Context compacted");
+  });
+});
diff --git a/packages/app/src/components/message-compaction-label.ts b/packages/app/src/components/message-compaction-label.ts
new file mode 100644
index 000000000..052d1d690
--- /dev/null
+++ b/packages/app/src/components/message-compaction-label.ts
@@ -0,0 +1,17 @@
+export interface CompactionMarkerLabelInput {
+  status: "loading" | "completed";
+  trigger?: "auto" | "manual";
+  preTokens?: number;
+}
+
+export function getCompactionMarkerLabel({
+  status,
+  trigger,
+  preTokens,
+}: CompactionMarkerLabelInput): string {
+  if (status === "loading") return "Compacting...";
+  if (trigger === "auto") return "Context automatically compacted";
+  if (trigger === "manual") return "Context manually compacted";
+  if (preTokens) return `Context compacted (${Math.round(preTokens / 1000)}K tokens)`;
+  return "Context compacted";
+}
diff --git a/packages/app/src/components/message.tsx b/packages/app/src/components/message.tsx
index b53cb2f01..8864a778a 100644
--- a/packages/app/src/components/message.tsx
+++ b/packages/app/src/components/message.tsx
@@ -92,6 +92,7 @@ import {
 import { PlanCard } from "./plan-card";
 import { useToolCallSheet } from "./tool-call-sheet";
 import { ToolCallDetailsContent } from "./tool-call-details";
+import { getCompactionMarkerLabel } from "./message-compaction-label";
 import { useAttachmentPreviewUrl } from "@/attachments/use-attachment-preview-url";
 import { persistAttachmentFromBytes, persistAttachmentFromDataUrl } from "@/attachments/service";
 import type { DaemonClient } from "@server/client/daemon-client";
@@ -1978,6 +1979,7 @@ export const ActivityLog = memo(function ActivityLog({
 
 interface CompactionMarkerProps {
   status: "loading" | "completed";
+  trigger?: "auto" | "manual";
   preTokens?: number;
 }
 
@@ -2008,12 +2010,10 @@ const compactionStylesheet = StyleSheet.create((theme) => ({
 
 export const CompactionMarker = memo(function CompactionMarker({
   status,
+  trigger,
   preTokens,
 }: CompactionMarkerProps) {
-  let label: string;
-  if (status === "loading") label = "Compacting...";
-  else if (preTokens) label = `Context compacted (${Math.round(preTokens / 1000)}K tokens)`;
-  else label = "Context compacted";
+  const label = getCompactionMarkerLabel({ status, trigger, preTokens });
 
   return (
     <View style={compactionStylesheet.container}>
diff --git a/packages/server/src/server/agent/providers/codex-app-server-agent.test.ts b/packages/server/src/server/agent/providers/codex-app-server-agent.test.ts
index 7729df953..3308607db 100644
--- a/packages/server/src/server/agent/providers/codex-app-server-agent.test.ts
+++ b/packages/server/src/server/agent/providers/codex-app-server-agent.test.ts
@@ -1290,6 +1290,10 @@ describe("Codex app-server provider", () => {
                     id: "message-history",
                     text: "History loaded.",
                   },
+                  {
+                    type: "contextCompaction",
+                    id: "compact-history",
+                  },
                 ],
               },
             ],
@@ -1318,6 +1322,14 @@ describe("Codex app-server provider", () => {
           messageId: "message-history",
         },
       },
+      {
+        type: "timeline",
+        provider: "codex",
+        item: {
+          type: "compaction",
+          status: "completed",
+        },
+      },
     ]);
   });
 
@@ -1380,6 +1392,116 @@ describe("Codex app-server provider", () => {
     ]);
   });
 
+  test("emits Codex context compaction markers from live thread items", () => {
+    const session = createSession();
+    const events: AgentStreamEvent[] = [];
+    session.subscribe((event) => events.push(event));
+
+    asInternals(session).handleNotification("item/started", {
+      threadId: "test-thread",
+      item: {
+        type: "contextCompaction",
+        id: "compact-live",
+      },
+    });
+    asInternals(session).handleNotification("item/completed", {
+      threadId: "test-thread",
+      item: {
+        type: "contextCompaction",
+        id: "compact-live",
+      },
+    });
+
+    expect(events).toEqual([
+      {
+        type: "timeline",
+        provider: "codex",
+        turnId: "test-turn",
+        item: {
+          type: "compaction",
+          status: "loading",
+        },
+      },
+      {
+        type: "timeline",
+        provider: "codex",
+        turnId: "test-turn",
+        item: {
+          type: "compaction",
+          status: "completed",
+        },
+      },
+    ]);
+  });
+
+  test("emits and dedupes Codex thread/compacted notifications", () => {
+    const session = createSession();
+    session.activeForegroundTurnId = null;
+    const events: AgentStreamEvent[] = [];
+    session.subscribe((event) => events.push(event));
+
+    asInternals(session).handleNotification("thread/compacted", {
+      threadId: "test-thread",
+      turnId: "legacy-compact-turn",
+    });
+    asInternals(session).handleNotification("item/completed", {
+      threadId: "test-thread",
+      item: {
+        type: "contextCompaction",
+        id: "legacy-compact-item",
+      },
+    });
+
+    expect(events).toEqual([
+      {
+        type: "timeline",
+        provider: "codex",
+        turnId: "legacy-compact-turn",
+        item: {
+          type: "compaction",
+          status: "completed",
+        },
+      },
+    ]);
+  });
+
+  test("emits consecutive Codex thread/compacted notifications", () => {
+    const session = createSession();
+    session.activeForegroundTurnId = null;
+    const events: AgentStreamEvent[] = [];
+    session.subscribe((event) => events.push(event));
+
+    asInternals(session).handleNotification("thread/compacted", {
+      threadId: "test-thread",
+      turnId: "legacy-compact-turn-1",
+    });
+    asInternals(session).handleNotification("thread/compacted", {
+      threadId: "test-thread",
+      turnId: "legacy-compact-turn-2",
+    });
+
+    expect(events).toEqual([
+      {
+        type: "timeline",
+        provider: "codex",
+        turnId: "legacy-compact-turn-1",
+        item: {
+          type: "compaction",
+          status: "completed",
+        },
+      },
+      {
+        type: "timeline",
+        provider: "codex",
+        turnId: "legacy-compact-turn-2",
+        item: {
+          type: "compaction",
+          status: "completed",
+        },
+      },
+    ]);
+  });
+
   test("does not replace a persisted Codex thread when app-server resume fails", async () => {
     const session = createSession({ thinkingOptionId: "medium" });
     session.currentThreadId = "archived-thread-id";
@@ -1450,6 +1572,77 @@ describe("Codex app-server provider", () => {
     ]);
   });
 
+  test("lists /compact and sends Codex compaction out of band", async () => {
+    const requests: Array<{ method: string; params: unknown }> = [];
+    const session = createSession();
+    session.client = {
+      request: vi.fn(async (method: string, params: unknown) => {
+        requests.push({ method, params });
+        if (method === "thread/loaded/list") {
+          return { data: ["test-thread"] };
+        }
+        if (method === "skills/list") {
+          return { data: [] };
+        }
+        return {};
+      }),
+    };
+
+    await expect(session.listCommands?.()).resolves.toContainEqual({
+      name: "compact",
+      description: "Summarize conversation to prevent hitting the context limit",
+      argumentHint: "",
+    });
+
+    const handler = session.tryHandleOutOfBand?.("/compact");
+    expect(handler).not.toBeNull();
+
+    const events: AgentStreamEvent[] = [];
+    session.subscribe((event) => events.push(event));
+    await handler?.run({ emit: (event) => events.push(event) });
+    asInternals(session).handleNotification("item/started", {
+      threadId: "test-thread",
+      item: {
+        type: "contextCompaction",
+        id: "manual-compact",
+      },
+    });
+    asInternals(session).handleNotification("item/completed", {
+      threadId: "test-thread",
+      item: {
+        type: "contextCompaction",
+        id: "manual-compact",
+      },
+    });
+
+    expect(requests).toContainEqual({
+      method: "thread/compact/start",
+      params: { threadId: "test-thread" },
+    });
+    expect(events).toEqual([
+      {
+        type: "timeline",
+        provider: "codex",
+        turnId: "test-turn",
+        item: {
+          type: "compaction",
+          status: "loading",
+          trigger: "manual",
+        },
+      },
+      {
+        type: "timeline",
+        provider: "codex",
+        turnId: "test-turn",
+        item: {
+          type: "compaction",
+          status: "completed",
+          trigger: "manual",
+        },
+      },
+    ]);
+  });
+
   test("maps question responses from headers back to question ids and completes the tool call", async () => {
     const session = createSession();
     const events: AgentStreamEvent[] = [];
diff --git a/packages/server/src/server/agent/providers/codex-app-server-agent.ts b/packages/server/src/server/agent/providers/codex-app-server-agent.ts
index 2fe97fa86..e5637c7c0 100644
--- a/packages/server/src/server/agent/providers/codex-app-server-agent.ts
+++ b/packages/server/src/server/agent/providers/codex-app-server-agent.ts
@@ -98,6 +98,7 @@ const CODEX_TOOL_THREAD_ITEM_TYPES = new Set([
   "webSearch",
   "collabAgentToolCall",
 ]);
+const CODEX_CONTEXT_COMPACTION_TYPE = "contextCompaction";
 const CODEX_PLAN_IMPLEMENTATION_PROMPT_PREFIX =
   "The user approved the plan. Implement it now. Do not restate or revise the plan unless blocked.";
 
@@ -1546,6 +1547,11 @@ function threadItemToTimeline(
       return mapCodexThreadPlanItem(normalizedItem);
     case "reasoning":
       return mapCodexThreadReasoningItem(normalizedItem);
+    case CODEX_CONTEXT_COMPACTION_TYPE:
+      return {
+        type: "compaction",
+        status: "completed",
+      };
     default:
       return null;
   }
@@ -1729,6 +1735,13 @@ const ItemLifecycleNotificationSchema = z
   })
   .passthrough();
 
+const ContextCompactedNotificationSchema = z
+  .object({
+    threadId: z.string(),
+    turnId: z.string().optional(),
+  })
+  .passthrough();
+
 const CodexEventTurnAbortedNotificationSchema = z
   .object({
     msg: z
@@ -1958,6 +1971,7 @@ type ParsedCodexNotification =
       itemId: string;
       delta: string | null;
     }
+  | { kind: "context_compacted"; threadId: string; turnId: string | null }
   | { kind: "invalid_payload"; method: string; params: unknown }
   | { kind: "unknown_method"; method: string; params: unknown };
 
@@ -2056,6 +2070,22 @@ const CodexNotificationSchema = z.union([
       params,
     }),
   ),
+  z
+    .object({ method: z.literal("thread/compacted"), params: ContextCompactedNotificationSchema })
+    .transform(
+      ({ params }): ParsedCodexNotification => ({
+        kind: "context_compacted",
+        threadId: params.threadId,
+        turnId: params.turnId ?? null,
+      }),
+    ),
+  z.object({ method: z.literal("thread/compacted"), params: z.unknown() }).transform(
+    ({ method, params }): ParsedCodexNotification => ({
+      kind: "invalid_payload",
+      method,
+      params,
+    }),
+  ),
   z
     .object({
       method: z.literal("item/agentMessage/delta"),
@@ -2679,6 +2709,12 @@ class CodexAppServerAgentSession implements AgentSession {
   private warnedIncompleteEditToolCallIds = new Set<string>();
   private latestUsage: AgentUsage | undefined;
   private latestPlanResult: { callId: string; text: string; turnId: string | null } | null = null;
+  private pendingManualCompactionStarts = 0;
+  private compactionTriggerByItemId = new Map<string, "auto" | "manual">();
+  // Codex can report one completed compaction through both channels:
+  // `thread/compacted` and a completed `contextCompaction` item.
+  private unpairedCompactionNotificationCompletions = 0;
+  private unpairedCompactionItemCompletions = 0;
   private connected = false;
   private collaborationModes: Array<{
     name: string;
@@ -3610,7 +3646,13 @@ class CodexAppServerAgentSession implements AgentSession {
       appServerSkills.length === 0
         ? await listCodexSkills(this.config.cwd, this.deps.workspaceGitService)
         : [];
-    const builtin: AgentSlashCommand[] = [];
+    const builtin: AgentSlashCommand[] = [
+      {
+        name: "compact",
+        description: "Summarize conversation to prevent hitting the context limit",
+        argumentHint: "",
+      },
+    ];
     if (this.goalsEnabled) {
       builtin.push({
         name: "goal",
@@ -3626,10 +3668,26 @@ class CodexAppServerAgentSession implements AgentSession {
   tryHandleOutOfBand(
     prompt: AgentPromptInput,
   ): { run(ctx: { emit: (event: AgentStreamEvent) => void }): Promise<void> } | null {
-    if (!this.goalsEnabled) return null;
     if (typeof prompt !== "string") return null;
     const parsed = this.parseSlashCommandInput(prompt);
-    if (!parsed || parsed.commandName !== "goal") return null;
+    if (!parsed) return null;
+
+    if (parsed.commandName === "compact") {
+      return {
+        run: async ({ emit }) => {
+          const error = await this.executeCompactCommand();
+          if (error) {
+            emit({
+              type: "timeline",
+              provider: CODEX_PROVIDER,
+              item: { type: "assistant_message", text: formatOutOfBandStatusMessage(error) },
+            });
+          }
+        },
+      };
+    }
+
+    if (!this.goalsEnabled || parsed.commandName !== "goal") return null;
 
     const subcommand = parseGoalSubcommand(parsed.args);
     return {
@@ -3644,6 +3702,33 @@ class CodexAppServerAgentSession implements AgentSession {
     };
   }
 
+  private async executeCompactCommand(): Promise<string | null> {
+    try {
+      await this.connect();
+      if (this.currentThreadId) {
+        await this.ensureThreadLoaded();
+      } else {
+        await this.ensureThread();
+      }
+      if (!this.client || !this.currentThreadId) {
+        throw new Error("Codex thread is not available");
+      }
+      this.pendingManualCompactionStarts += 1;
+      try {
+        await this.client.request("thread/compact/start", {
+          threadId: this.currentThreadId,
+        });
+      } catch (error) {
+        this.pendingManualCompactionStarts = Math.max(0, this.pendingManualCompactionStarts - 1);
+        throw error;
+      }
+      return null;
+    } catch (error) {
+      const message = error instanceof Error ? error.message : "unknown error";
+      return `Failed to compact context: ${message}`;
+    }
+  }
+
   private async executeGoalSubcommand(subcommand: GoalSubcommand): Promise<string> {
     if (subcommand.kind === "usage") {
       return "Usage: /goal <objective>|pause|resume|clear";
@@ -3875,6 +3960,9 @@ class CodexAppServerAgentSession implements AgentSession {
       case "token_usage_updated":
         this.handleTokenUsageUpdatedNotification(parsed);
         return;
+      case "context_compacted":
+        this.handleContextCompactedNotification(parsed);
+        return;
       case "agent_message_delta":
       case "reasoning_delta":
       case "exec_command_output_delta":
@@ -4201,6 +4289,8 @@ class CodexAppServerAgentSession implements AgentSession {
     this.pendingFileChangeOutputDeltas.clear();
     this.pendingAssistantMessageBoundary = false;
     this.warnedIncompleteEditToolCallIds.clear();
+    this.unpairedCompactionNotificationCompletions = 0;
+    this.unpairedCompactionItemCompletions = 0;
   }
 
   private handlePlanUpdatedNotification(
@@ -4240,6 +4330,65 @@ class CodexAppServerAgentSession implements AgentSession {
     }
   }
 
+  private resolveContextCompactionTrigger(itemId?: string): "auto" | "manual" | undefined {
+    if (itemId) {
+      const known = this.compactionTriggerByItemId.get(itemId);
+      if (known) {
+        return known;
+      }
+    }
+    if (this.pendingManualCompactionStarts > 0) {
+      this.pendingManualCompactionStarts -= 1;
+      return "manual";
+    }
+    return undefined;
+  }
+
+  private createContextCompactionTimelineItem(
+    status: "loading" | "completed",
+    itemId?: string,
+  ): Extract<AgentTimelineItem, { type: "compaction" }> {
+    const trigger = this.resolveContextCompactionTrigger(itemId);
+    if (itemId && trigger) {
+      if (status === "loading") {
+        this.compactionTriggerByItemId.set(itemId, trigger);
+      } else {
+        this.compactionTriggerByItemId.delete(itemId);
+      }
+    }
+    return {
+      type: "compaction",
+      status,
+      ...(trigger ? { trigger } : {}),
+    };
+  }
+
+  private isContextCompactionItem(item: { type?: string; [key: string]: unknown }): boolean {
+    return (
+      normalizeCodexThreadItemType(typeof item.type === "string" ? item.type : undefined) ===
+      CODEX_CONTEXT_COMPACTION_TYPE
+    );
+  }
+
+  private handleContextCompactedNotification(
+    parsed: Extract<ParsedCodexNotification, { kind: "context_compacted" }>,
+  ): void {
+    if (parsed.threadId !== this.currentThreadId) {
+      return;
+    }
+    if (this.unpairedCompactionItemCompletions > 0) {
+      this.unpairedCompactionItemCompletions -= 1;
+      return;
+    }
+    this.unpairedCompactionNotificationCompletions += 1;
+    this.emitEvent({
+      type: "timeline",
+      provider: CODEX_PROVIDER,
+      item: this.createContextCompactionTimelineItem("completed"),
+      ...(parsed.turnId ? { turnId: parsed.turnId } : {}),
+    });
+  }
+
   private handleExecCommandStartedNotification(
     parsed: Extract<ParsedCodexNotification, { kind: "exec_command_started" }>,
   ): void {
@@ -4357,6 +4506,19 @@ class CodexAppServerAgentSession implements AgentSession {
     if (parsed.source === "codex_event") {
       return;
     }
+    if (this.isContextCompactionItem(parsed.item)) {
+      if (this.unpairedCompactionNotificationCompletions > 0) {
+        this.unpairedCompactionNotificationCompletions -= 1;
+        return;
+      }
+      this.emitEvent({
+        type: "timeline",
+        provider: CODEX_PROVIDER,
+        item: this.createContextCompactionTimelineItem("completed", parsed.item.id),
+      });
+      this.unpairedCompactionItemCompletions += 1;
+      return;
+    }
     const timelineItem = threadItemToTimeline(parsed.item, {
       includeUserMessage: false,
       cwd: this.config.cwd ?? null,
@@ -4487,6 +4649,14 @@ class CodexAppServerAgentSession implements AgentSession {
     if (parsed.source === "codex_event") {
       return;
     }
+    if (this.isContextCompactionItem(parsed.item)) {
+      this.emitEvent({
+        type: "timeline",
+        provider: CODEX_PROVIDER,
+        item: this.createContextCompactionTimelineItem("loading", parsed.item.id),
+      });
+      return;
+    }
     const timelineItem = threadItemToTimeline(parsed.item, {
       includeUserMessage: false,
       cwd: this.config.cwd ?? null,