diff --git a/src/agent-manager.ts b/src/agent-manager.ts
index bfc3cc93..0f3c0c97 100644
--- a/src/agent-manager.ts
+++ b/src/agent-manager.ts
@@ -106,7 +106,7 @@ interface SpawnOptions {
   /** Called at the end of each agentic turn with the cumulative count. */
   onTurnEnd?: (turnCount: number) => void;
   /** Called once per assistant message_end with that message's usage delta. */
-  onAssistantUsage?: (usage: { input: number; output: number; cacheWrite: number }) => void;
+  onAssistantUsage?: (usage: { input: number; output: number; cacheWrite: number; cost?: number }) => void;
   /** Called when the session successfully compacts. */
   onCompaction?: (info: CompactionInfo) => void;
   /** Nesting depth: top-level subagent = 1. */
diff --git a/src/agent-runner.ts b/src/agent-runner.ts
index 362e9a8c..b21aa846 100644
--- a/src/agent-runner.ts
+++ b/src/agent-runner.ts
@@ -396,7 +396,7 @@ export interface RunOptions {
    * Lets callers maintain a lifetime accumulator that survives compaction
    * (which replaces session.state.messages and resets stats-derived sums).
    */
-  onAssistantUsage?: (usage: { input: number; output: number; cacheWrite: number }) => void;
+  onAssistantUsage?: (usage: { input: number; output: number; cacheWrite: number; cost?: number }) => void;
   /**
    * Called when the session successfully compacts. `tokensBefore` is upstream's
    * pre-compaction context size estimate. Aborted compactions don't fire.
@@ -935,11 +935,15 @@ export async function runAgent(
     }
     if (event.type === "message_end" && event.message.role === "assistant") {
       const u = (event.message as any).usage;
-      if (u) options.onAssistantUsage?.({
-        input: u.input ?? 0,
-        output: u.output ?? 0,
-        cacheWrite: u.cacheWrite ?? 0,
-      });
+      if (u) {
+        const cost = typeof u.cost?.total === "number" && Number.isFinite(u.cost.total) ? u.cost.total : undefined;
+        options.onAssistantUsage?.({
+          input: u.input ?? 0,
+          output: u.output ?? 0,
+          cacheWrite: u.cacheWrite ?? 0,
+          ...(cost !== undefined ? { cost } : {}),
+        });
+      }
     }
     if (event.type === "compaction_end" && !event.aborted && event.result) {
       options.onCompaction?.({ reason: event.reason, tokensBefore: event.result.tokensBefore });
@@ -981,7 +985,7 @@ export async function resumeAgent(
   prompt: string,
   options: {
     onToolActivity?: (activity: ToolActivity) => void;
-    onAssistantUsage?: (usage: { input: number; output: number; cacheWrite: number }) => void;
+    onAssistantUsage?: (usage: { input: number; output: number; cacheWrite: number; cost?: number }) => void;
     onCompaction?: (info: { reason: "manual" | "threshold" | "overflow"; tokensBefore: number }) => void;
     signal?: AbortSignal;
   } = {},
@@ -999,11 +1003,15 @@ export async function resumeAgent(
         if (event.type === "tool_execution_end") options.onToolActivity?.({ type: "end", toolName: event.toolName });
         if (event.type === "message_end" && event.message.role === "assistant") {
           const u = (event.message as any).usage;
-          if (u) options.onAssistantUsage?.({
-            input: u.input ?? 0,
-            output: u.output ?? 0,
-            cacheWrite: u.cacheWrite ?? 0,
-          });
+          if (u) {
+            const cost = typeof u.cost?.total === "number" && Number.isFinite(u.cost.total) ? u.cost.total : undefined;
+            options.onAssistantUsage?.({
+              input: u.input ?? 0,
+              output: u.output ?? 0,
+              cacheWrite: u.cacheWrite ?? 0,
+              ...(cost !== undefined ? { cost } : {}),
+            });
+          }
         }
         if (event.type === "compaction_end" && !event.aborted && event.result) {
           options.onCompaction?.({ reason: event.reason, tokensBefore: event.result.tokensBefore });
diff --git a/src/index.ts b/src/index.ts
index 8736dd23..0ca9883b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -32,7 +32,7 @@ import { SubagentScheduler } from "./schedule.js";
 import { resolveStorePath, ScheduleStore } from "./schedule-store.js";
 import { applyAndEmitLoaded, type SubagentsSettings, saveAndEmitChanged, type ToolDescriptionMode } from "./settings.js";
 import { getForegroundOutcomeNote, getStatusNote, partialOutputSuffix } from "./status-note.js";
-import { type AgentConfig, type AgentInvocation, type AgentRecord, type JoinMode, type NotificationDetails, type SubagentType, type WidgetMode } from "./types.js";
+import { type AgentConfig, type AgentInvocation, type AgentRecord, type GroupSummary, type JoinMode, type NotificationDetails, type SubagentType, type WidgetMode } from "./types.js";
 import {
   type AgentActivity,
   type AgentDetails,
@@ -52,7 +52,7 @@ import {
 } from "./ui/agent-widget.js";
 import { FleetList, type FleetUICtx } from "./ui/fleet-list.js";
 import { showSchedulesMenu } from "./ui/schedule-menu.js";
-import { addUsage, getLifetimeTotal, getSessionContextPercent, type LifetimeUsage } from "./usage.js";
+import { addUsage, formatCost, getLifetimeTotal, getSessionContextPercent, type LifetimeUsage } from "./usage.js";
 
 // ---- Shared helpers ----
 
@@ -79,6 +79,23 @@ function formatLifetimeTokens(o: { lifetimeUsage: LifetimeUsage }): string {
   return t > 0 ? formatTokens(t) : "";
 }
 
+/** Format an agent's reported model cost, or "" when unavailable. */
+function formatLifetimeCost(o: { lifetimeUsage: LifetimeUsage }): string {
+  return formatCost(o.lifetimeUsage.cost);
+}
+
+/** Format aggregate stats for a grouped notification. */
+export function formatGroupSummary(summary: GroupSummary, includeCost: boolean): string {
+  const countLabel = `${summary.count} agent${summary.count === 1 ? "" : "s"} completed${summary.partial ? " (partial)" : ""}`;
+  const parts = [countLabel];
+  if (summary.totalTokens > 0) parts.push(formatTokens(summary.totalTokens));
+  if (includeCost) {
+    const cost = formatCost(summary.totalCost);
+    if (cost) parts.push(cost);
+  }
+  return parts.join(" · ");
+}
+
 /**
  * Create an AgentActivity state and spawn callbacks for tracking tool usage.
  * Used by both foreground and background paths to avoid duplication.
@@ -117,7 +134,7 @@ function createActivityTracker(maxTurns?: number, onStreamUpdate?: () => void) {
     onSessionCreated: (session: any) => {
       state.session = session;
     },
-    onAssistantUsage: (usage: { input: number; output: number; cacheWrite: number }) => {
+    onAssistantUsage: (usage: { input: number; output: number; cacheWrite: number; cost?: number }) => {
       addUsage(state.lifetimeUsage, usage);
       onStreamUpdate?.();
     },
@@ -152,7 +169,7 @@ function escapeXml(s: string): string {
 }
 
 /** Format a structured task notification matching Claude Code's <task-notification> XML. */
-function formatTaskNotification(record: AgentRecord, resultMaxLen: number): string {
+function formatTaskNotification(record: AgentRecord, resultMaxLen: number, includeCost = false): string {
   const status = getStatusLabel(record.status, record.error);
   const durationMs = record.completedAt ? record.completedAt - record.startedAt : 0;
   const totalTokens = getLifetimeTotal(record.lifetimeUsage);
@@ -174,7 +191,7 @@ function formatTaskNotification(record: AgentRecord, resultMaxLen: number): stri
     `<status>${escapeXml(status)}</status>`,
     `<summary>Agent "${escapeXml(record.description)}" ${record.status}${getStatusNote(record.status)}</summary>`,
     `<result>${escapeXml(resultPreview)}</result>`,
-    `<usage><total_tokens>${totalTokens}</total_tokens><tool_uses>${record.toolUses}</tool_uses>${ctxXml}${compactXml}<duration_ms>${durationMs}</duration_ms></usage>`,
+    `<usage><total_tokens>${totalTokens}</total_tokens><tool_uses>${record.toolUses}</tool_uses>${ctxXml}${compactXml}${includeCost && record.lifetimeUsage.cost !== undefined ? `<cost>${record.lifetimeUsage.cost}</cost>` : ""}<duration_ms>${durationMs}</duration_ms></usage>`,
     `</task-notification>`,
   ].filter(Boolean).join('\n');
 }
@@ -190,6 +207,7 @@ function buildDetails(
     ...base,
     toolUses: record.toolUses,
     tokens: formatLifetimeTokens(record),
+    cost: record.lifetimeUsage.cost,
     turnCount: activity?.turnCount,
     maxTurns: activity?.maxTurns,
     durationMs: (record.completedAt ?? Date.now()) - record.startedAt,
@@ -212,6 +230,7 @@ function buildNotificationDetails(record: AgentRecord, resultMaxLen: number, act
     turnCount: activity?.turnCount ?? 0,
     maxTurns: activity?.maxTurns,
     totalTokens,
+    cost: record.lifetimeUsage.cost,
     durationMs: record.completedAt ? record.completedAt - record.startedAt : 0,
     outputFile: record.outputFile,
     error: record.error,
@@ -229,6 +248,11 @@ export default function (pi: ExtensionAPI) {
   // injected as scoped custom tools by the existing manager instead.
   if (inChildSessionContext()) return;
 
+  let costDisplayEnabled = false;
+  function isCostDisplayEnabled(): boolean { return costDisplayEnabled; }
+  let groupSummaryEnabled = false;
+  function isGroupSummaryEnabled(): boolean { return groupSummaryEnabled; }
+
   // ---- Register custom notification renderer ----
   pi.registerMessageRenderer<NotificationDetails>(
     "subagent-notification",
@@ -251,6 +275,7 @@ export default function (pi: ExtensionAPI) {
         if (d.turnCount > 0) parts.push(formatTurns(d.turnCount, d.maxTurns));
         if (d.toolUses > 0) parts.push(`${d.toolUses} tool use${d.toolUses === 1 ? "" : "s"}`);
         if (d.totalTokens > 0) parts.push(formatTokens(d.totalTokens));
+        if (isCostDisplayEnabled() && d.cost !== undefined) parts.push(formatCost(d.cost));
         if (d.durationMs > 0) parts.push(formatMs(d.durationMs));
         if (parts.length) {
           line += "\n  " + parts.map(p => theme.fg("dim", p)).join(" " + theme.fg("dim", "·") + " ");
@@ -274,7 +299,12 @@ export default function (pi: ExtensionAPI) {
       }
 
       const all = [d, ...(d.others ?? [])];
-      return new Text(all.map(renderOne).join("\n"), 0, 0);
+      const summary = isGroupSummaryEnabled() && d.groupSummary
+        ? formatGroupSummary(d.groupSummary, isCostDisplayEnabled())
+        : "";
+      const rendered = all.map(renderOne);
+      if (summary) rendered.unshift(theme.fg("dim", summary));
+      return new Text(rendered.join("\n"), 0, 0);
     }
   );
 
@@ -319,7 +349,7 @@ export default function (pi: ExtensionAPI) {
   function emitIndividualNudge(record: AgentRecord) {
     if (record.resultConsumed) return;  // re-check at send time
 
-    const notification = formatTaskNotification(record, 500);
+    const notification = formatTaskNotification(record, 500, isCostDisplayEnabled());
     const footer = record.outputFile ? `\nFull transcript available at: ${record.outputFile}` : '';
 
     pi.sendMessage<NotificationDetails>({
@@ -349,13 +379,22 @@ export default function (pi: ExtensionAPI) {
         const unconsumed = records.filter(r => !r.resultConsumed);
         if (unconsumed.length === 0) { widget.update(); return; }
 
-        const notifications = unconsumed.map(r => formatTaskNotification(r, 300)).join('\n\n');
+        const notifications = unconsumed.map(r => formatTaskNotification(r, 300, isCostDisplayEnabled())).join('\n\n');
         const label = partial
           ? `${unconsumed.length} agent(s) finished (partial — others still running)`
           : `${unconsumed.length} agent(s) finished`;
 
         const [first, ...rest] = unconsumed;
+        const costs = unconsumed
+          .map((record) => record.lifetimeUsage.cost)
+          .filter((cost): cost is number => cost !== undefined && Number.isFinite(cost));
         const details = buildNotificationDetails(first, 300, agentActivity.get(first.id));
+        details.groupSummary = {
+          count: unconsumed.length,
+          partial,
+          totalTokens: unconsumed.reduce((total, record) => total + getLifetimeTotal(record.lifetimeUsage), 0),
+          totalCost: costs.length === unconsumed.length ? costs.reduce((total, cost) => total + cost, 0) : undefined,
+        };
         if (rest.length > 0) {
           details.others = rest.map(r => buildNotificationDetails(r, 300, agentActivity.get(r.id)));
         }
@@ -602,11 +641,13 @@ export default function (pi: ExtensionAPI) {
   // everything else; "off" = hide the widget entirely. Read live at render time.
   let widgetMode: WidgetMode = "background";
   function getWidgetMode(): WidgetMode { return widgetMode; }
-  const widget = new AgentWidget(manager, agentActivity, getWidgetMode);
+  const widget = new AgentWidget(manager, agentActivity, getWidgetMode, isCostDisplayEnabled);
   function setWidgetMode(m: WidgetMode): void { widgetMode = m; widget.update(); }
+  function setCostDisplayEnabled(b: boolean): void { costDisplayEnabled = b; widget.update(); }
+  function setGroupSummaryEnabled(b: boolean): void { groupSummaryEnabled = b; }
 
   // Claude Code-style FleetView: navigable list of main + subagents below the editor.
-  const fleet = new FleetList(manager, agentActivity);
+  const fleet = new FleetList(manager, agentActivity, isCostDisplayEnabled);
   let fleetViewEnabled = true;
   function isFleetViewEnabled(): boolean { return fleetViewEnabled; }
   function setFleetViewEnabled(b: boolean): void { fleetViewEnabled = b; fleet.setEnabled(b); }
@@ -762,6 +803,8 @@ export default function (pi: ExtensionAPI) {
       setOutputTranscript: setOutputTranscriptDefault,
       setMaxSubagentDepth: setMaxSubagentDepth,
       setFallbackSubagent: setFallbackSubagent,
+      setShowCost: setCostDisplayEnabled,
+      setShowGroupSummary: setGroupSummaryEnabled,
     },
     (event, payload) => pi.events.emit(event, payload),
   );
@@ -986,6 +1029,7 @@ Terse command-style prompts produce shallow, generic work.
         }
         if (d.toolUses > 0) parts.push(`${d.toolUses} tool use${d.toolUses === 1 ? "" : "s"}`);
         if (d.tokens) parts.push(d.tokens);
+        if (isCostDisplayEnabled() && d.cost !== undefined) parts.push(formatCost(d.cost));
         return parts.map(p => fgPreservingNestedStyles(theme, "dim", p)).join(" " + theme.fg("dim", "·") + " ");
       };
 
@@ -1325,6 +1369,7 @@ Terse command-style prompts produce shallow, generic work.
           ...detailBase,
           toolUses: fgState.toolUses,
           tokens: formatLifetimeTokens(fgState),
+          cost: fgState.lifetimeUsage.cost,
           turnCount: fgState.turnCount,
           maxTurns: fgState.maxTurns,
           durationMs: Date.now() - startedAt,
@@ -1421,6 +1466,10 @@ Terse command-style prompts produce shallow, generic work.
       const durationMs = (record.completedAt ?? Date.now()) - record.startedAt;
       const statsParts = [`${record.toolUses} tool uses`];
       if (tokenText) statsParts.push(tokenText);
+      if (isCostDisplayEnabled()) {
+        const costText = formatLifetimeCost(record);
+        if (costText) statsParts.push(costText);
+      }
       return textResult(
         `${fallbackNote}Agent completed in ${formatMs(durationMs)} (${statsParts.join(", ")})${getForegroundOutcomeNote(record.status)}.\n\n` +
         (record.result?.trim() || "No output."),
@@ -1479,6 +1528,10 @@ Terse command-style prompts produce shallow, generic work.
       const contextPercent = getSessionContextPercent(record.session);
       const statsParts = [`Tool uses: ${record.toolUses}`];
       if (tokens) statsParts.push(tokens);
+      if (isCostDisplayEnabled()) {
+        const costText = formatLifetimeCost(record);
+        if (costText) statsParts.push(`Cost: ${costText}`);
+      }
       if (contextPercent !== null) statsParts.push(`Context: ${Math.round(contextPercent)}%`);
       if (record.compactionCount) statsParts.push(`Compactions: ${record.compactionCount}`);
       statsParts.push(`Duration: ${duration}`);
@@ -1554,6 +1607,10 @@ Terse command-style prompts produce shallow, generic work.
         const contextPercent = getSessionContextPercent(record.session);
         const stateParts: string[] = [];
         if (tokens) stateParts.push(tokens);
+        if (isCostDisplayEnabled()) {
+          const costText = formatLifetimeCost(record);
+          if (costText) stateParts.push(costText);
+        }
         stateParts.push(`${record.toolUses} tool ${record.toolUses === 1 ? "use" : "uses"}`);
         if (contextPercent !== null) stateParts.push(`context ${Math.round(contextPercent)}% full`);
         if (record.compactionCount) stateParts.push(`${record.compactionCount} compaction${record.compactionCount === 1 ? "" : "s"}`);
@@ -1772,7 +1829,7 @@ Terse command-style prompts produce shallow, generic work.
           if (manager.abort(record.id)) {
             ctx.ui.notify(`Stopped "${record.description}".`, "info");
           }
-        }, keybindings, (message: string) => manager.steer(record.id, message));
+        }, keybindings, (message: string) => manager.steer(record.id, message), isCostDisplayEnabled);
       },
       {
         overlay: true,
@@ -2152,6 +2209,8 @@ ${systemPrompt}
       // explicit configuration — which then fails loudly if general-purpose later
       // goes away. undefined is dropped by JSON.stringify.
       fallbackSubagent: getFallbackSubagent(),
+      showCost: isCostDisplayEnabled(),
+      showGroupSummary: isGroupSummaryEnabled(),
     };
   }
 
@@ -2242,6 +2301,20 @@ ${systemPrompt}
           currentValue: getOutputTranscriptDefault() ? "on" : "off",
           values: ["on", "off"],
         },
+        {
+          id: "showCost",
+          label: "Cost display",
+          description: "Show reported model cost in agent progress and results",
+          currentValue: isCostDisplayEnabled() ? "on" : "off",
+          values: ["on", "off"],
+        },
+        {
+          id: "showGroupSummary",
+          label: "Group summary",
+          description: "Show aggregate stats for grouped background-agent notifications",
+          currentValue: isGroupSummaryEnabled() ? "on" : "off",
+          values: ["on", "off"],
+        },
         {
           id: "fleetView",
           label: "Fleet view",
@@ -2334,6 +2407,14 @@ ${systemPrompt}
         const enabled = value === "on";
         setOutputTranscriptDefault(enabled);
         notifyApplied(ctx, `Output transcript ${enabled ? "enabled" : "disabled"} by default`);
+      } else if (id === "showCost") {
+        const enabled = value === "on";
+        setCostDisplayEnabled(enabled);
+        notifyApplied(ctx, `Cost display ${enabled ? "enabled" : "disabled"}`);
+      } else if (id === "showGroupSummary") {
+        const enabled = value === "on";
+        setGroupSummaryEnabled(enabled);
+        notifyApplied(ctx, `Group summary ${enabled ? "enabled" : "disabled"}`);
       } else if (id === "toolDescriptionMode") {
         setToolDescriptionMode(value as ToolDescriptionMode);
         notifyApplied(ctx, `Tool description set to ${value}. Takes effect on next pi session.`);
diff --git a/src/settings.ts b/src/settings.ts
index ac6299dd..4aa77310 100644
--- a/src/settings.ts
+++ b/src/settings.ts
@@ -117,6 +117,10 @@ export interface SubagentsSettings {
    * meaning one thing here and another in the resolver.
    */
   fallbackSubagent?: string;
+  /** Whether to show reported model costs in subagent UI and results. Defaults to false. */
+  showCost?: boolean;
+  /** Whether to show aggregate stats for grouped background-agent notifications. Defaults to false. */
+  showGroupSummary?: boolean;
 }
 
 export type ToolDescriptionMode = "full" | "compact" | "custom";
@@ -136,6 +140,8 @@ export interface SettingsAppliers {
   setOutputTranscript: (b: boolean) => void;
   setMaxSubagentDepth: (n: number) => void;
   setFallbackSubagent: (v: string | undefined) => void;
+  setShowCost: (b: boolean) => void;
+  setShowGroupSummary: (b: boolean) => void;
 }
 
 /** Emit callback — a subset of `pi.events.emit` to keep helpers testable. */
@@ -220,6 +226,12 @@ function sanitize(raw: unknown): SubagentsSettings {
   } else if (typeof r.fallbackSubagent === "string" && r.fallbackSubagent.trim()) {
     out.fallbackSubagent = r.fallbackSubagent.trim();
   }
+  if (typeof r.showCost === "boolean") {
+    out.showCost = r.showCost;
+  }
+  if (typeof r.showGroupSummary === "boolean") {
+    out.showGroupSummary = r.showGroupSummary;
+  }
   return out;
 }
 
@@ -283,6 +295,8 @@ export function applySettings(s: SubagentsSettings, appliers: SettingsAppliers):
   if (typeof s.fleetView === "boolean") appliers.setFleetView(s.fleetView);
   if (s.widgetMode) appliers.setWidgetMode(s.widgetMode);
   if (typeof s.outputTranscript === "boolean") appliers.setOutputTranscript(s.outputTranscript);
+  if (typeof s.showCost === "boolean") appliers.setShowCost(s.showCost);
+  if (typeof s.showGroupSummary === "boolean") appliers.setShowGroupSummary(s.showGroupSummary);
 }
 
 /**
diff --git a/src/types.ts b/src/types.ts
index 3d566aa4..0ea9d799 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -115,7 +115,8 @@ export interface AgentRecord {
   /**
    * Lifetime usage breakdown, accumulated via `message_end` events. Survives
    * compaction. Total = input + output + cacheWrite (cacheRead deliberately
-   * excluded — see issue #38). Initialized to zeros at spawn.
+   * excluded — see issue #38). Reported model cost is accumulated separately
+   * when available. Initialized to zeros at spawn.
    */
   lifetimeUsage: LifetimeUsage;
   /** Number of times this agent's session has compacted. Initialized to 0 at spawn. */
@@ -158,6 +159,15 @@ export interface AgentInvocation {
   isolation?: IsolationMode;
 }
 
+/** Aggregate stats attached to a grouped notification. */
+export interface GroupSummary {
+  count: number;
+  partial: boolean;
+  totalTokens: number;
+  /** Sum of reported model costs, when available for every member. */
+  totalCost?: number;
+}
+
 /** Details attached to custom notification messages for visual rendering. */
 export interface NotificationDetails {
   id: string;
@@ -171,6 +181,10 @@ export interface NotificationDetails {
   outputFile?: string;
   error?: string;
   resultPreview: string;
+  /** Reported model cost, when available. */
+  cost?: number;
+  /** Aggregate stats for a grouped notification. */
+  groupSummary?: GroupSummary;
   /** Additional agents in a group notification. */
   others?: NotificationDetails[];
 }
diff --git a/src/ui/agent-widget.ts b/src/ui/agent-widget.ts
index 3cbe9cc8..90195957 100644
--- a/src/ui/agent-widget.ts
+++ b/src/ui/agent-widget.ts
@@ -9,7 +9,7 @@ import { truncateToWidth } from "@earendil-works/pi-tui";
 import type { AgentManager } from "../agent-manager.js";
 import { getConfig } from "../agent-types.js";
 import type { AgentInvocation, SubagentType, WidgetMode } from "../types.js";
-import { getLifetimeTotal, getSessionContextPercent, type LifetimeUsage, type SessionLike } from "../usage.js";
+import { formatCost, getLifetimeTotal, getSessionContextPercent, type LifetimeUsage, type SessionLike } from "../usage.js";
 
 // ---- Constants ----
 
@@ -84,6 +84,8 @@ export interface AgentDetails {
   turnCount?: number;
   /** Effective max turns (undefined = unlimited). */
   maxTurns?: number;
+  /** Reported model cost, when available. */
+  cost?: number;
   agentId?: string;
   error?: string;
 }
@@ -237,6 +239,7 @@ export class AgentWidget {
      * extension supplies one defaulting to `"background"`.
      */
     private mode: () => WidgetMode = () => "all",
+    private showCost: () => boolean = () => false,
   ) {}
 
   /**
@@ -306,7 +309,7 @@ export class AgentWidget {
   }
 
   /** Render a finished agent line. */
-  private renderFinishedLine(a: { id: string; type: SubagentType; status: string; description: string; toolUses: number; startedAt: number; completedAt?: number; error?: string }, theme: Theme): string {
+  private renderFinishedLine(a: { id: string; type: SubagentType; status: string; description: string; toolUses: number; startedAt: number; completedAt?: number; error?: string; lifetimeUsage: LifetimeUsage }, theme: Theme): string {
     const name = getDisplayName(a.type);
     const modeLabel = getPromptModeLabel(a.type);
     const duration = formatMs((a.completedAt ?? Date.now()) - a.startedAt);
@@ -336,6 +339,11 @@ export class AgentWidget {
     const activity = this.agentActivity.get(a.id);
     if (activity) parts.push(formatTurns(activity.turnCount, activity.maxTurns));
     if (a.toolUses > 0) parts.push(`${a.toolUses} tool use${a.toolUses === 1 ? "" : "s"}`);
+    const totalTokens = getLifetimeTotal(a.lifetimeUsage);
+    if (totalTokens > 0) parts.push(formatTokens(totalTokens));
+    if (this.showCost() && a.lifetimeUsage.cost !== undefined) {
+      parts.push(formatCost(a.lifetimeUsage.cost));
+    }
     parts.push(duration);
 
     const modeTag = modeLabel ? ` ${theme.fg("dim", `(${modeLabel})`)}` : "";
@@ -384,7 +392,8 @@ export class AgentWidget {
 
       const bg = this.agentActivity.get(a.id);
       const toolUses = bg?.toolUses ?? a.toolUses;
-      const tokens = getLifetimeTotal(bg?.lifetimeUsage);
+      const usage = bg?.lifetimeUsage ?? a.lifetimeUsage;
+      const tokens = getLifetimeTotal(usage);
       const contextPercent = getSessionContextPercent(bg?.session);
       const tokenText = tokens > 0 ? formatSessionTokens(tokens, contextPercent, theme, a.compactionCount) : "";
 
@@ -392,6 +401,7 @@ export class AgentWidget {
       if (bg) parts.push(formatTurns(bg.turnCount, bg.maxTurns));
       if (toolUses > 0) parts.push(`${toolUses} tool use${toolUses === 1 ? "" : "s"}`);
       if (tokenText) parts.push(tokenText);
+      if (this.showCost() && usage.cost !== undefined) parts.push(formatCost(usage.cost));
       parts.push(elapsed);
       const statsText = parts.join(" · ");
 
diff --git a/src/ui/conversation-viewer.ts b/src/ui/conversation-viewer.ts
index e482344e..12a69f09 100644
--- a/src/ui/conversation-viewer.ts
+++ b/src/ui/conversation-viewer.ts
@@ -9,7 +9,7 @@ import type { AgentSession } from "@earendil-works/pi-coding-agent";
 import { type Component, Input, matchesKey, type TUI, truncateToWidth, visibleWidth, wrapTextWithAnsi } from "@earendil-works/pi-tui";
 import { extractText } from "../context.js";
 import type { AgentRecord } from "../types.js";
-import { getLifetimeTotal, getSessionContextPercent } from "../usage.js";
+import { formatCost, getLifetimeTotal, getSessionContextPercent } from "../usage.js";
 import type { Theme } from "./agent-widget.js";
 import { type AgentActivity, buildInvocationTags, describeActivity, fgPreservingNestedStyles, formatDuration, formatSessionTokens, getDisplayName, getPromptModeLabel } from "./agent-widget.js";
 import { createViewerKeys, type ViewerKeybindings, type ViewerKeys } from "./viewer-keys.js";
@@ -45,6 +45,8 @@ export class ConversationViewer implements Component {
     keybindings?: ViewerKeybindings,
     /** Send a steering message to the agent. Omitted → no compose affordance. */
     private onSteer?: (message: string) => void,
+    /** Read live cost-display preference. Omitted → hide reported cost. */
+    private showCost: () => boolean = () => false,
   ) {
     this.keys = createViewerKeys(keybindings);
     this.unsubscribe = session.subscribe(() => {
@@ -152,11 +154,15 @@ export class ConversationViewer implements Component {
     const headerParts: string[] = [duration];
     const toolUses = this.activity?.toolUses ?? this.record.toolUses;
     if (toolUses > 0) headerParts.unshift(`${toolUses} tool${toolUses === 1 ? "" : "s"}`);
-    const tokens = getLifetimeTotal(this.activity?.lifetimeUsage);
+    const usage = this.activity?.lifetimeUsage ?? this.record.lifetimeUsage;
+    const tokens = getLifetimeTotal(usage);
     if (tokens > 0) {
       const percent = getSessionContextPercent(this.activity?.session);
       headerParts.push(formatSessionTokens(tokens, percent, th, this.record.compactionCount));
     }
+    if (this.showCost() && usage?.cost !== undefined) {
+      headerParts.push(formatCost(usage.cost));
+    }
 
     lines.push(row(
       `${statusIcon} ${th.bold(name)}${modeTag}  ${th.fg("muted", this.record.description)} ${th.fg("dim", "·")} ${fgPreservingNestedStyles(th, "dim", headerParts.join(" · "))}`,
diff --git a/src/ui/fleet-list.ts b/src/ui/fleet-list.ts
index 3727b05e..29f16c85 100644
--- a/src/ui/fleet-list.ts
+++ b/src/ui/fleet-list.ts
@@ -14,7 +14,7 @@
 import { Editor, isKeyRelease, Key, matchesKey, truncateToWidth, visibleWidth } from "@earendil-works/pi-tui";
 import type { AgentManager } from "../agent-manager.js";
 import type { AgentRecord } from "../types.js";
-import { getLifetimeTotal } from "../usage.js";
+import { formatCost, getLifetimeTotal } from "../usage.js";
 import { type AgentActivity, getDisplayName, type Theme } from "./agent-widget.js";
 import { ConversationViewer, VIEWPORT_HEIGHT_PCT } from "./conversation-viewer.js";
 
@@ -93,6 +93,7 @@ export class FleetList {
   constructor(
     private manager: AgentManager,
     private agentActivity: Map<string, AgentActivity>,
+    private showCost: () => boolean = () => false,
   ) {}
 
   // ---- Lifecycle ----
@@ -310,6 +311,7 @@ export class FleetList {
           },
           keybindings,
           (message: string) => this.manager.steer(record.id, message),
+          this.showCost,
         );
       },
       {
@@ -372,9 +374,14 @@ export class FleetList {
 
   private renderAgentRow(rosterIndex: number, sel: number, record: AgentRecord, width: number, theme: Theme): string {
     const left = `  ${this.bullet(rosterIndex, sel, theme)} ${theme.fg("muted", getDisplayName(record.type))}  ${record.description}`;
-    const tokens = getLifetimeTotal(this.agentActivity.get(record.id)?.lifetimeUsage ?? record.lifetimeUsage);
+    const usage = this.agentActivity.get(record.id)?.lifetimeUsage ?? record.lifetimeUsage;
+    const tokens = getLifetimeTotal(usage);
     const elapsedMs = (record.completedAt ?? Date.now()) - record.startedAt; // freezes once finished
-    const right = theme.fg("dim", `${formatFleetElapsed(elapsedMs)} · ${formatFleetTokens(tokens)}`);
+    const cost = this.showCost() ? formatCost(usage.cost) : "";
+    const stats = [formatFleetElapsed(elapsedMs), formatFleetTokens(tokens), cost]
+      .filter(Boolean)
+      .join(" · ");
+    const right = theme.fg("dim", stats);
     return rightAlign(left, right, width);
   }
 }
diff --git a/src/usage.ts b/src/usage.ts
index 9fe075a9..152e0087 100644
--- a/src/usage.ts
+++ b/src/usage.ts
@@ -5,9 +5,10 @@
  * compaction (which replaces session.state.messages and would reset any
  * stats-derived sum). cacheRead is excluded because each turn's cacheRead is
  * the cumulative cached prefix re-read on that one call — summing across
- * turns counts the prefix N times. See issue #38.
+ * turns counts the prefix N times. See issue #38. Reported model cost is
+ * accumulated separately when the provider supplies it.
  */
-export type LifetimeUsage = { input: number; output: number; cacheWrite: number };
+export type LifetimeUsage = { input: number; output: number; cacheWrite: number; cost?: number };
 
 /** Sum of lifetime usage components, or 0 if undefined. */
 export function getLifetimeTotal(u?: LifetimeUsage): number {
@@ -19,6 +20,12 @@ export function addUsage(into: LifetimeUsage, delta: LifetimeUsage): void {
   into.input += delta.input;
   into.output += delta.output;
   into.cacheWrite += delta.cacheWrite;
+  if (delta.cost !== undefined) into.cost = (into.cost ?? 0) + delta.cost;
+}
+
+/** Format a reported model cost for compact UI display, or "" when unavailable. */
+export function formatCost(cost?: number): string {
+  return cost !== undefined && Number.isFinite(cost) ? `~$${cost.toFixed(3)}` : "";
 }
 
 /** Minimal shape we read from upstream `getSessionStats()`. */
diff --git a/test/agent-manager.test.ts b/test/agent-manager.test.ts
index 35e20563..531c687c 100644
--- a/test/agent-manager.test.ts
+++ b/test/agent-manager.test.ts
@@ -582,8 +582,8 @@ describe("AgentManager — lifetime usage + compaction count are eagerly initial
     vi.mocked(runAgent).mockImplementation(async (_ctx, _type, _prompt, opts: any) => {
       captured = opts;
       // Two assistant messages with usage
-      opts.onAssistantUsage?.({ input: 100, output: 50, cacheWrite: 10 });
-      opts.onAssistantUsage?.({ input: 200, output: 80, cacheWrite: 20 });
+      opts.onAssistantUsage?.({ input: 100, output: 50, cacheWrite: 10, cost: 0.012 });
+      opts.onAssistantUsage?.({ input: 200, output: 80, cacheWrite: 20, cost: 0.006 });
       return { responseText: "done", session: mockSession(), aborted: false, steered: false };
     });
 
@@ -594,9 +594,11 @@ describe("AgentManager — lifetime usage + compaction count are eagerly initial
     await manager.getRecord(id)!.promise;
 
     expect(captured).toBeDefined();
-    expect(manager.getRecord(id)!.lifetimeUsage).toEqual({
-      input: 300, output: 130, cacheWrite: 30,
-    });
+    const usage = manager.getRecord(id)!.lifetimeUsage;
+    expect(usage.input).toBe(300);
+    expect(usage.output).toBe(130);
+    expect(usage.cacheWrite).toBe(30);
+    expect(usage.cost).toBeCloseTo(0.018);
   });
 
   it("onCompaction from runAgent increments record.compactionCount", async () => {
diff --git a/test/agent-runner.test.ts b/test/agent-runner.test.ts
index 34790f08..099929d9 100644
--- a/test/agent-runner.test.ts
+++ b/test/agent-runner.test.ts
@@ -533,6 +533,24 @@ describe("agent-runner usage callback wiring", () => {
     expect(seen).toEqual([{ input: 50, output: 0, cacheWrite: 0 }]);
   });
 
+  it("runAgent forwards reported cost when message_end includes it", async () => {
+    const { session, listeners } = createSession("OK");
+    createAgentSession.mockResolvedValue({ session });
+
+    const seen: any[] = [];
+    session.prompt = vi.fn(async () => {
+      emitMessageEnd(listeners, { input: 50, output: 10, cacheWrite: 2, cost: { total: 0.018 } });
+      session.messages.push({ role: "assistant", content: [{ type: "text", text: "OK" }] });
+    });
+
+    await runAgent(ctx, "Explore", "go", {
+      pi,
+      onAssistantUsage: (u) => seen.push(u),
+    });
+
+    expect(seen).toEqual([{ input: 50, output: 10, cacheWrite: 2, cost: 0.018 }]);
+  });
+
   it("runAgent skips the callback when message_end has no usage field", async () => {
     const { session, listeners } = createSession("OK");
     createAgentSession.mockResolvedValue({ session });
@@ -553,7 +571,7 @@ describe("agent-runner usage callback wiring", () => {
     const seen: any[] = [];
 
     session.prompt = vi.fn(async () => {
-      emitMessageEnd(listeners, { input: 10, output: 20, cacheWrite: 5 });
+      emitMessageEnd(listeners, { input: 10, output: 20, cacheWrite: 5, cost: { total: 0.004 } });
       session.messages.push({ role: "assistant", content: [{ type: "text", text: "RESUMED" }] });
     });
 
@@ -561,7 +579,7 @@ describe("agent-runner usage callback wiring", () => {
       onAssistantUsage: (u) => seen.push(u),
     });
 
-    expect(seen).toEqual([{ input: 10, output: 20, cacheWrite: 5 }]);
+    expect(seen).toEqual([{ input: 10, output: 20, cacheWrite: 5, cost: 0.004 }]);
   });
 
   it("forwards compaction_end events to onCompaction (only when not aborted)", async () => {
diff --git a/test/agent-widget.test.ts b/test/agent-widget.test.ts
index 6bed6cf1..83f1284f 100644
--- a/test/agent-widget.test.ts
+++ b/test/agent-widget.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { renderRunningAgentStatus } from "../src/index.js";
+import { formatGroupSummary, renderRunningAgentStatus } from "../src/index.js";
 import type { WidgetMode } from "../src/types.js";
 import { type AgentActivity, AgentWidget, fgPreservingNestedStyles, formatSessionTokens } from "../src/ui/agent-widget.js";
 
@@ -54,28 +54,55 @@ describe("renderRunningAgentStatus", () => {
   });
 });
 
+describe("formatGroupSummary", () => {
+  const summary = {
+    count: 3,
+    partial: false,
+    totalTokens: 42_200,
+    totalCost: 0.042,
+  };
+
+  it("shows aggregate token usage without cost when cost display is disabled", () => {
+    expect(formatGroupSummary(summary, false)).toBe("3 agents completed · 42.2k token");
+  });
+
+  it("includes aggregate cost only when cost display is enabled", () => {
+    expect(formatGroupSummary(summary, true)).toBe("3 agents completed · 42.2k token · ~$0.042");
+  });
+
+  it("marks partial groups", () => {
+    expect(formatGroupSummary({ ...summary, partial: true }, false)).toBe("3 agents completed (partial) · 42.2k token");
+  });
+});
+
 describe("AgentWidget", () => {
   const theme = { fg: (_c: string, s: string) => s, bold: (s: string) => s };
 
-  function makeActivity(): AgentActivity {
+  function makeActivity(cost?: number): AgentActivity {
     return {
       activeTools: new Map(),
       toolUses: 0,
       responseText: "",
       turnCount: 1,
-      lifetimeUsage: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+      lifetimeUsage: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, cost },
     };
   }
 
-  function makeRecord(id: string, opts: { isBackground?: boolean; parentAgentId?: string } = {}) {
+  function makeRecord(id: string, opts: {
+    isBackground?: boolean;
+    parentAgentId?: string;
+    status?: "running" | "steered";
+    lifetimeUsage?: { input: number; output: number; cacheWrite: number; cost?: number };
+  } = {}) {
     return {
       id,
       type: "general-purpose",
       description: `${id} description`,
-      status: "running",
+      status: opts.status ?? "running",
       toolUses: 0,
       startedAt: Date.now(),
-      lifetimeUsage: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+      completedAt: opts.status === "steered" ? Date.now() : undefined,
+      lifetimeUsage: opts.lifetimeUsage ?? { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
       compactionCount: 0,
       isBackground: opts.isBackground,
       parentAgentId: opts.parentAgentId,
@@ -83,11 +110,12 @@ describe("AgentWidget", () => {
   }
 
   /** Render the widget for a manager and return the produced lines ("" if nothing rendered). */
-  function renderLines(manager: unknown, activityId: string, mode?: () => WidgetMode): string {
+  function renderLines(manager: unknown, activityId: string, mode?: () => WidgetMode, showCost?: () => boolean, cost?: number): string {
     const widget = new AgentWidget(
       manager as any,
-      new Map([[activityId, makeActivity()]]),
+      new Map([[activityId, makeActivity(cost)]]),
       mode,
+      showCost,
     );
     let factory: any;
     widget.setUICtx({
@@ -139,6 +167,30 @@ describe("AgentWidget", () => {
   });
 
   // "off" hides the widget entirely — even a background agent renders nothing.
+  it("shows cost only when cost display is enabled", () => {
+    const manager = { listAgents: () => [makeRecord("background", { isBackground: true })] };
+    expect(renderLines(manager, "background", () => "background", () => false, 0.018)).not.toContain("~$0.018");
+    expect(renderLines(manager, "background", () => "background", () => true, 0.018)).toContain("~$0.018");
+  });
+
+  it("keeps lifetime tokens and cost on a finished turn-limited agent", () => {
+    const manager = {
+      listAgents: () => [makeRecord("limited", {
+        isBackground: true,
+        status: "steered",
+        lifetimeUsage: { input: 1_000, output: 200, cacheWrite: 0, cost: 0.018 },
+      })],
+    };
+    const lines = renderLines(manager, "limited", () => "background", () => true);
+    const hiddenCostLines = renderLines(manager, "limited", () => "background", () => false);
+
+    expect(lines).toContain("1.2k token");
+    expect(lines).toContain("~$0.018");
+    expect(lines).toContain("turn limit");
+    expect(hiddenCostLines).toContain("1.2k token");
+    expect(hiddenCostLines).not.toContain("~$0.018");
+  });
+
   it("renders nothing in 'off' mode", () => {
     const manager = { listAgents: () => [makeRecord("background", { isBackground: true })] };
     expect(renderLines(manager, "background", () => "off")).toBe("");
diff --git a/test/conversation-viewer.test.ts b/test/conversation-viewer.test.ts
index d1aedad2..238f085b 100644
--- a/test/conversation-viewer.test.ts
+++ b/test/conversation-viewer.test.ts
@@ -257,6 +257,42 @@ describe("ConversationViewer", () => {
     });
   });
 
+  describe("cost display", () => {
+    it("shows reported lifetime cost when enabled", () => {
+      const viewer = new ConversationViewer(
+        mockTui(),
+        mockSession(),
+        mockRecord({ lifetimeUsage: { input: 1_000, output: 200, cacheWrite: 0, cost: 0.018 } }),
+        undefined,
+        ansiTheme(),
+        vi.fn(),
+        undefined,
+        undefined,
+        undefined,
+        () => true,
+      );
+
+      expect(viewer.render(80).join("\n")).toContain("~$0.018");
+    });
+
+    it("hides reported lifetime cost when disabled", () => {
+      const viewer = new ConversationViewer(
+        mockTui(),
+        mockSession(),
+        mockRecord({ lifetimeUsage: { input: 1_000, output: 200, cacheWrite: 0, cost: 0.018 } }),
+        undefined,
+        ansiTheme(),
+        vi.fn(),
+        undefined,
+        undefined,
+        undefined,
+        () => false,
+      );
+
+      expect(viewer.render(80).join("\n")).not.toContain("~$0.018");
+    });
+  });
+
   describe("safety net against upstream wrapTextWithAnsi bugs", () => {
     // These tests call buildContentLines() directly (via the private method)
     // because render() has its own truncation via row(). The safety net in
diff --git a/test/fleet-list.test.ts b/test/fleet-list.test.ts
index 7d91c286..210e8468 100644
--- a/test/fleet-list.test.ts
+++ b/test/fleet-list.test.ts
@@ -49,7 +49,7 @@ interface Harness {
   ui: FleetUICtx;
   manager: AgentManager;
   /** The overlay component (a real ConversationViewer) once one is opened. */
-  overlayComponent: () => { handleInput(data: string): void } | undefined;
+  overlayComponent: () => { handleInput(data: string): void; render(width: number): string[] } | undefined;
   /** Feed a key to the registered input handler; returns the consume result. */
   press: (data: string) => { consume?: boolean } | undefined;
   /** Render the currently-registered below-editor widget at the given width. */
@@ -65,7 +65,7 @@ interface Harness {
   widgetTui: { requestRender(): void; focusedComponent?: unknown };
 }
 
-function harness(agents: AgentRecord[]): Harness {
+function harness(agents: AgentRecord[], showCost = false): Harness {
   let inputHandler: ((data: string) => { consume?: boolean } | undefined) | undefined;
   let widgetFactory: ((tui: any, theme: any) => { render(w: number): string[] }) | undefined;
   let editorText = "";
@@ -93,7 +93,7 @@ function harness(agents: AgentRecord[]): Harness {
   };
 
   const manager = fakeManager(agents);
-  const fleet = new FleetList(manager, new Map());
+  const fleet = new FleetList(manager, new Map(), () => showCost);
   fleet.setUICtx(ui);
   fleet.update();
 
@@ -315,6 +315,35 @@ describe("FleetList rendering", () => {
     expect(agentLine).toMatch(/\d+s · ↓/); // "<seconds>s · ↓ ..." (timing-agnostic)
   });
 
+  it("shows reported cost when cost display is enabled", () => {
+    const h = harness([
+      makeRecord({ lifetimeUsage: { input: 13_100, output: 0, cacheWrite: 0, cost: 0.018 } }),
+    ], true);
+    const agentLine = h.render(120).find(l => l.includes("Sleep then report 1"))!;
+    expect(agentLine).toContain("~$0.018");
+  });
+
+  it("passes cost display to the selected agent popup", () => {
+    const h = harness([
+      makeRecord({ lifetimeUsage: { input: 13_100, output: 0, cacheWrite: 0, cost: 0.018 } }),
+    ], true);
+    h.press(DOWN);  // activate (main)
+    h.press(DOWN);  // select the agent
+    h.press(ENTER); // open the conversation popup
+
+    // The harness theme uses visible markup instead of ANSI escapes; use a wide
+    // render width so that markup does not affect the viewer's truncation path.
+    expect(h.overlayComponent()!.render(500).join("\n")).toContain("~$0.018");
+  });
+
+  it("hides reported cost when cost display is disabled", () => {
+    const h = harness([
+      makeRecord({ lifetimeUsage: { input: 13_100, output: 0, cacheWrite: 0, cost: 0.018 } }),
+    ]);
+    const agentLine = h.render(120).find(l => l.includes("Sleep then report 1"))!;
+    expect(agentLine).not.toContain("~$0.018");
+  });
+
   it("orders agents earliest-launched first (top)", () => {
     const agents = [
       makeRecord({ id: "new", description: "newest", startedAt: 2000 }),
diff --git a/test/settings.test.ts b/test/settings.test.ts
index af83b841..d19098b4 100644
--- a/test/settings.test.ts
+++ b/test/settings.test.ts
@@ -284,6 +284,38 @@ describe("settings persistence", () => {
       expect(loadSettings(projectDir).scopeModels).toBeUndefined();
     });
 
+    it("accepts showCost boolean (true and false)", () => {
+      writeProject({ showCost: true });
+      expect(loadSettings(projectDir)).toEqual({ showCost: true });
+      writeProject({ showCost: false });
+      expect(loadSettings(projectDir)).toEqual({ showCost: false });
+    });
+
+    it("drops non-boolean showCost", () => {
+      writeProject({ showCost: "yes" });
+      expect(loadSettings(projectDir).showCost).toBeUndefined();
+      writeProject({ showCost: 1 });
+      expect(loadSettings(projectDir).showCost).toBeUndefined();
+      writeProject({ showCost: null });
+      expect(loadSettings(projectDir).showCost).toBeUndefined();
+    });
+
+    it("accepts showGroupSummary boolean (true and false)", () => {
+      writeProject({ showGroupSummary: true });
+      expect(loadSettings(projectDir)).toEqual({ showGroupSummary: true });
+      writeProject({ showGroupSummary: false });
+      expect(loadSettings(projectDir)).toEqual({ showGroupSummary: false });
+    });
+
+    it("drops non-boolean showGroupSummary", () => {
+      writeProject({ showGroupSummary: "yes" });
+      expect(loadSettings(projectDir).showGroupSummary).toBeUndefined();
+      writeProject({ showGroupSummary: 1 });
+      expect(loadSettings(projectDir).showGroupSummary).toBeUndefined();
+      writeProject({ showGroupSummary: null });
+      expect(loadSettings(projectDir).showGroupSummary).toBeUndefined();
+    });
+
     it("accepts disableDefaultAgents boolean (true and false)", () => {
       writeProject({ disableDefaultAgents: true });
       expect(loadSettings(projectDir)).toEqual({ disableDefaultAgents: true });
@@ -420,6 +452,8 @@ describe("settings persistence", () => {
         setOutputTranscript: vi.fn(),
         setMaxSubagentDepth: vi.fn(),
         setFallbackSubagent: vi.fn(),
+        setShowCost: vi.fn(),
+        setShowGroupSummary: vi.fn(),
       };
     });
 
@@ -466,6 +500,8 @@ describe("settings persistence", () => {
           toolDescriptionMode: "compact",
           fleetView: false,
           widgetMode: "off",
+          showCost: true,
+          showGroupSummary: true,
         },
         appliers,
       );
@@ -479,6 +515,8 @@ describe("settings persistence", () => {
       expect(appliers.setToolDescriptionMode).toHaveBeenCalledWith("compact");
       expect(appliers.setFleetView).toHaveBeenCalledWith(false);
       expect(appliers.setWidgetMode).toHaveBeenCalledWith("off");
+      expect(appliers.setShowCost).toHaveBeenCalledWith(true);
+      expect(appliers.setShowGroupSummary).toHaveBeenCalledWith(true);
     });
 
     it("applies widgetMode; skips it when absent", () => {
@@ -517,6 +555,13 @@ describe("settings persistence", () => {
       expect(appliers.setOutputTranscript).toHaveBeenCalledWith(true);
     });
 
+    it("applies showGroupSummary (both true and false)", () => {
+      applySettings({ showGroupSummary: false }, appliers);
+      expect(appliers.setShowGroupSummary).toHaveBeenCalledWith(false);
+      applySettings({ showGroupSummary: true }, appliers);
+      expect(appliers.setShowGroupSummary).toHaveBeenCalledWith(true);
+    });
+
     it("applies defaultMaxTurns: 0 as the explicit unlimited marker", () => {
       applySettings({ defaultMaxTurns: 0 }, appliers);
       expect(appliers.setDefaultMaxTurns).toHaveBeenCalledWith(0);
@@ -578,6 +623,8 @@ describe("settings persistence", () => {
         setOutputTranscript: vi.fn(),
         setMaxSubagentDepth: vi.fn(),
         setFallbackSubagent: vi.fn(),
+        setShowCost: vi.fn(),
+        setShowGroupSummary: vi.fn(),
       };
     });
 
diff --git a/test/usage.test.ts b/test/usage.test.ts
index 4300925e..aa9eba1d 100644
--- a/test/usage.test.ts
+++ b/test/usage.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { getLifetimeTotal, getSessionContextPercent, getSessionTokens } from "../src/usage.js";
+import { addUsage, formatCost, getLifetimeTotal, getSessionContextPercent, getSessionTokens } from "../src/usage.js";
 
 // Regression for issue #38 — token semantics + context indicator
 describe("usage", () => {
@@ -50,6 +50,26 @@ describe("usage", () => {
     });
   });
 
+  describe("cost", () => {
+    it("accumulates reported cost without affecting token totals", () => {
+      const usage = { input: 100, output: 20, cacheWrite: 5 };
+      addUsage(usage, { input: 10, output: 2, cacheWrite: 1, cost: 0.012 });
+      addUsage(usage, { input: 20, output: 3, cacheWrite: 0, cost: 0.006 });
+
+      expect(usage.input).toBe(130);
+      expect(usage.output).toBe(25);
+      expect(usage.cacheWrite).toBe(6);
+      expect(usage.cost).toBeCloseTo(0.018);
+      expect(getLifetimeTotal(usage)).toBe(161);
+    });
+
+    it("formats reported cost and omits unavailable values", () => {
+      expect(formatCost(0.018)).toBe("~$0.018");
+      expect(formatCost(undefined)).toBe("");
+      expect(formatCost(Number.NaN)).toBe("");
+    });
+  });
+
   describe("getLifetimeTotal", () => {
     it("sums components and handles undefined", () => {
       expect(getLifetimeTotal(undefined)).toBe(0);