diff --git a/src/features/chat/components/chat-input.tsx b/src/features/chat/components/chat-input.tsx
index 06cf1bba..c3809002 100644
--- a/src/features/chat/components/chat-input.tsx
+++ b/src/features/chat/components/chat-input.tsx
@@ -16,9 +16,11 @@ import {
   useChatInputController,
 } from "~/features/chat/hooks/use-chat-input-controller";
 import { useChatUIStore } from "~/features/chat/store";
+import { useUserSettings } from "~/features/settings/hooks/use-user-settings";
 import { cn } from "~/lib/utils";
 
 import { ChatInputCapabilities } from "./chat-input-capabilities";
+import { ContextWindowBar } from "./context-window-bar";
 import { ModelSelector } from "./ui/model-selector";
 
 type ChatInputProps = {
@@ -26,6 +28,7 @@ type ChatInputProps = {
   sendMessage: UseChatHelpers<ChatUIMessage>["sendMessage"];
   isLoading?: boolean;
   onStop?: () => void;
+  messages?: ChatUIMessage[];
 };
 
 export function ChatInput({
@@ -33,6 +36,7 @@ export function ChatInput({
   sendMessage,
   isLoading = false,
   onStop,
+  messages = [],
 }: ChatInputProps) {
   const { input, apiStatus, model, features, attachments, send } = useChatInputController({
     sendMessage,
@@ -40,6 +44,11 @@ export function ChatInput({
     onStop,
   });
   const isIncognito = useChatUIStore(state => state.isIncognito);
+  const { data: settings } = useUserSettings();
+  const contextWindowDisplay = settings?.contextWindowDisplay ?? "auto";
+
+  const selectedModel = model.favorites.find(m => m.id === model.selectedId);
+  const contextLength = selectedModel?.contextLength ?? 0;
 
   return (
     <div className={cn(`bg-background p-4 pt-0`, className)}>
@@ -59,6 +68,11 @@ export function ChatInput({
             attachments.isDragging && "ring-primary ring-2",
           )}
         >
+          <ContextWindowBar
+            messages={messages}
+            contextLength={contextLength}
+            displayMode={contextWindowDisplay}
+          />
           {isIncognito && (
             <div className={`
               text-muted-foreground flex items-center gap-2 border-b
diff --git a/src/features/chat/components/chat-view.tsx b/src/features/chat/components/chat-view.tsx
index 950b4cfd..016554a0 100644
--- a/src/features/chat/components/chat-view.tsx
+++ b/src/features/chat/components/chat-view.tsx
@@ -63,6 +63,7 @@ export function ChatView({
           sendMessage={sendMessage}
           isLoading={isLoading}
           onStop={onStop}
+          messages={messages}
         />
       </div>
     </div>
diff --git a/src/features/chat/components/context-window-bar.tsx b/src/features/chat/components/context-window-bar.tsx
new file mode 100644
index 00000000..243d2058
--- /dev/null
+++ b/src/features/chat/components/context-window-bar.tsx
@@ -0,0 +1,128 @@
+"use client";
+
+import { useMemo, useState } from "react";
+
+import type { ChatUIMessage } from "~/features/chat/types";
+
+import { cn } from "~/lib/utils";
+
+type ContextWindowBarProps = {
+  messages: ChatUIMessage[];
+  contextLength: number;
+  displayMode: "disabled" | "auto" | "always";
+};
+
+export function ContextWindowBar({
+  messages,
+  contextLength,
+  displayMode,
+}: ContextWindowBarProps) {
+  const [isHovered, setIsHovered] = useState(false);
+
+  const { usedTokens, percentage } = useMemo(() => {
+    // Estimate context window usage by summing content that accumulates in history.
+    //
+    // We avoid using inputTokens from metadata because totalUsage.inputTokens
+    // is summed across all multi-step tool calls (search → extract → respond),
+    // dramatically over-counting the actual context size.
+    //
+    // Instead we estimate from the actual message content:
+    // - Assistant text/reasoning parts: estimate from character count (÷4)
+    // - Tool result parts: estimate from serialized output size (÷4)
+    //   (search sources, extracted content — these are the largest contributors)
+    // - User messages: estimate from character count (÷4)
+    // - Baseline: ~500 tokens for system prompt + tool definitions
+    const CHARS_PER_TOKEN = 4;
+    const SYSTEM_PROMPT_BASELINE = 500;
+    let total = SYSTEM_PROMPT_BASELINE;
+
+    for (const msg of messages) {
+      if (!msg.parts) continue;
+
+      for (const part of msg.parts) {
+        if (part.type === "text") {
+          total += Math.ceil(((part as { text: string }).text?.length ?? 0) / CHARS_PER_TOKEN);
+        }
+        else if (part.type === "reasoning") {
+          total += Math.ceil(((part as { text: string }).text?.length ?? 0) / CHARS_PER_TOKEN);
+        }
+        else if (part.type.startsWith("tool-")) {
+          const toolPart = part as { input?: unknown; output?: unknown };
+          const inputSize = toolPart.input ? JSON.stringify(toolPart.input).length : 0;
+          const outputSize = toolPart.output ? JSON.stringify(toolPart.output).length : 0;
+          total += Math.ceil((inputSize + outputSize) / CHARS_PER_TOKEN);
+        }
+        else if (part.type === "file") {
+          // File parts contribute their URL/data length
+          total += Math.ceil(((part as { url?: string }).url?.length ?? 0) / CHARS_PER_TOKEN);
+        }
+      }
+    }
+
+    const pct = contextLength > 0 ? Math.min((total / contextLength) * 100, 100) : 0;
+    return { usedTokens: total, percentage: pct };
+  }, [messages, contextLength]);
+
+  if (displayMode === "disabled") return null;
+  if (displayMode === "auto" && percentage < 25) return null;
+  if (contextLength === 0) return null;
+
+  const barColor = percentage >= 90
+    ? "bg-destructive"
+    : percentage >= 70
+      ? "bg-yellow-500"
+      : "bg-primary";
+
+  const formatTokens = (tokens: number) => {
+    if (tokens >= 1_000_000) return `${(tokens / 1_000_000).toFixed(1)}M`;
+    if (tokens >= 1_000) return `${(tokens / 1_000).toFixed(1)}k`;
+    return tokens.toLocaleString();
+  };
+
+  return (
+    <div
+      className={cn(
+        "relative w-full cursor-default overflow-hidden transition-all duration-300 ease-out",
+        isHovered ? "h-5" : "h-1",
+      )}
+      onMouseEnter={() => setIsHovered(true)}
+      onMouseLeave={() => setIsHovered(false)}
+      role="meter"
+      aria-valuenow={percentage}
+      aria-valuemin={0}
+      aria-valuemax={100}
+      aria-label={`Context window usage: ~${formatTokens(usedTokens)} / ${formatTokens(contextLength)} tokens (~${Math.round(percentage)}%)`}
+    >
+      {/* Background track */}
+      <div className="bg-muted/50 absolute inset-0" />
+
+      {/* Filled bar */}
+      <div
+        className={cn(
+          barColor,
+          "absolute inset-y-0 left-0 transition-all duration-500 ease-out",
+          isHovered ? "opacity-80" : "opacity-60",
+        )}
+        style={{ width: `${percentage}%` }}
+      />
+
+      {/* Label (visible on hover) */}
+      <div
+        className={cn(
+          "absolute inset-0 flex items-center justify-center transition-opacity duration-200",
+          isHovered ? "opacity-100" : "opacity-0",
+        )}
+      >
+        <span className="text-foreground text-[10px] font-medium leading-none drop-shadow-sm">
+          ~
+          {formatTokens(usedTokens)}
+          {" / "}
+          {formatTokens(contextLength)}
+          {" · ~"}
+          {Math.round(percentage)}
+          %
+        </span>
+      </div>
+    </div>
+  );
+}
diff --git a/src/features/settings/actions.ts b/src/features/settings/actions.ts
index fab61c06..2df0b7e4 100644
--- a/src/features/settings/actions.ts
+++ b/src/features/settings/actions.ts
@@ -118,6 +118,7 @@ export async function createDefaultUserSettings(userId: string): Promise<UserSet
     toolHandoffModel: "gemini-flash-lite",
     desktopNotifications: false,
     autoScrollDuringGeneration: true,
+    contextWindowDisplay: "auto",
     favoriteModels: STARTER_FAVORITE_MODELS,
   };
 
diff --git a/src/features/settings/components/pages/input-page.tsx b/src/features/settings/components/pages/input-page.tsx
index fe0f1654..1acacdaf 100644
--- a/src/features/settings/components/pages/input-page.tsx
+++ b/src/features/settings/components/pages/input-page.tsx
@@ -22,6 +22,12 @@ const keyboardShortcuts = [
   { label: "Unfocus Input", keys: ["Esc"] },
 ];
 
+const contextWindowDisplayOptions = [
+  { value: "disabled" as const, label: "Disabled" },
+  { value: "auto" as const, label: "Auto (>25%)" },
+  { value: "always" as const, label: "Always" },
+];
+
 const sendMessageKeyboardShortcutOptions = [
   { value: "enter" as const, label: <Kbd>Enter</Kbd> },
   { value: "ctrlEnter" as const, label: (
@@ -92,6 +98,15 @@ export function InputPage() {
             onChange={value => save({ sendMessageKeyboardShortcut: value })}
             layout="flex"
           />
+
+          <SelectionCardItem
+            label="Context Window Usage"
+            description="Show a bar at the top of the input box indicating how much of the model's context window has been used."
+            options={contextWindowDisplayOptions}
+            value={settings.contextWindowDisplay ?? "auto"}
+            onChange={value => save({ contextWindowDisplay: value })}
+            layout="flex"
+          />
         </SettingsSection>
 
         <Separator />
diff --git a/src/features/settings/queries.ts b/src/features/settings/queries.ts
index 4e52643a..9f3c708c 100644
--- a/src/features/settings/queries.ts
+++ b/src/features/settings/queries.ts
@@ -33,6 +33,7 @@ const DEFAULT_SETTINGS: UserSettingsData = {
   toolHandoffModel: "gemini-flash-lite",
   desktopNotifications: false,
   autoScrollDuringGeneration: true,
+  contextWindowDisplay: "auto",
   favoriteModels: STARTER_FAVORITE_MODELS,
 };
 
diff --git a/src/features/settings/types.ts b/src/features/settings/types.ts
index 48f5e971..0b4869f3 100644
--- a/src/features/settings/types.ts
+++ b/src/features/settings/types.ts
@@ -64,6 +64,7 @@ export const preferencesSchema = z.object({
   toolHandoffModel: z.enum(toolModelIds).default("gemini-flash-lite"),
   desktopNotifications: z.boolean().default(false),
   autoScrollDuringGeneration: z.boolean().default(true),
+  contextWindowDisplay: z.enum(["disabled", "auto", "always"]).default("auto"),
 });
 
 /**
@@ -96,6 +97,7 @@ export const preferencesUpdateSchema = z.object({
   toolHandoffModel: z.enum(toolModelIds).optional(),
   desktopNotifications: z.boolean().optional(),
   autoScrollDuringGeneration: z.boolean().optional(),
+  contextWindowDisplay: z.enum(["disabled", "auto", "always"]).optional(),
 });
 
 export type PreferencesInput = z.infer<typeof preferencesSchema>;
@@ -182,6 +184,7 @@ export type UserSettingsData = {
   toolHandoffModel: ToolModelId;
   desktopNotifications: boolean;
   autoScrollDuringGeneration: boolean;
+  contextWindowDisplay: "disabled" | "auto" | "always";
   // List of favorite model IDs from OpenRouter (max 10)
   favoriteModels?: string[];
   // Derived: which providers have a key configured (server can verify server-stored keys,