@@ -44,7 +44,7 @@ const clientSettings: ClientSettings = {
   fontFamilyComposer: "",
   fontFamilySans: "",
   fontFamilyTerminal: "",
-  fontSizeChat: 14,
+  fontSizeChat: null,
   fontSizeCode: 13,
   fontSizeInterface: 16,
   fontSizePrompt: 14,
 
@@ -1,5 +1,4 @@
 import {
-  DEFAULT_CHAT_FONT_SIZE,
   DEFAULT_CODE_FONT_SIZE,
   DEFAULT_INTERFACE_FONT_SIZE,
   DEFAULT_PROMPT_FONT_SIZE,
@@ -68,7 +67,7 @@ export interface AppearanceFontPreferences {
   readonly chat: string;
   readonly sizeInterface: number;
   readonly sizePrompt: number;
-  readonly sizeChat: number;
+  readonly sizeChat: number | null;
   readonly sizeCode: number;
   readonly smoothing: boolean;
 }
@@ -96,8 +95,7 @@ export function applyAppearanceFontVariables(
   root.style.fontSize = `${clampInterfaceFontSize(preferences.sizeInterface)}px`;
   root.style.setProperty("--font-size-prompt", `${clampPromptFontSize(preferences.sizePrompt)}px`);
   const chat = clampChatFontSize(preferences.sizeChat);
-  // The default leaves messages on their rem size, so they keep following the interface size.
-  if (chat === DEFAULT_CHAT_FONT_SIZE) {
+  if (chat === null) {
     root.style.removeProperty("--font-size-chat");
   } else {
     root.style.setProperty("--font-size-chat", `${chat}px`);
@@ -131,8 +129,9 @@ function clampPromptFontSize(value: number): number {
   return clampFontSize(value, MIN_PROMPT_FONT_SIZE, MAX_PROMPT_FONT_SIZE, DEFAULT_PROMPT_FONT_SIZE);
 }
 
-function clampChatFontSize(value: number): number {
-  return clampFontSize(value, MIN_CHAT_FONT_SIZE, MAX_CHAT_FONT_SIZE, DEFAULT_CHAT_FONT_SIZE);
+function clampChatFontSize(value: number | null): number | null {
+  if (value === null || !Number.isFinite(value)) return null;
+  return Math.min(MAX_CHAT_FONT_SIZE, Math.max(MIN_CHAT_FONT_SIZE, Math.round(value)));
 }
 
 function clampCodeFontSize(value: number): number {
 
@@ -119,6 +119,7 @@ function ChatFontRow() {
         value: settings.fontSizeChat,
         defaultValue: DEFAULT_UNIFIED_SETTINGS.fontSizeChat,
         onChange: (fontSizeChat) => updateSettings({ fontSizeChat }),
+        onClear: () => updateSettings({ fontSizeChat: null }),
       }}
       preview={<ChatFontPreview />}
     />
@@ -414,9 +415,11 @@ function FontFamilySettingsRow({
     label: string;
     min: number;
     max: number;
-    value: number;
-    defaultValue: number;
+    value: number | null;
+    defaultValue: number | null;
     onChange: (v: number) => void;
+    /** Adds a "Default" option that stores null. */
+    onClear?: () => void;
   };
 }) {
   const trimmed = value.trim();
@@ -535,19 +538,28 @@ function FontFamilySettingsRow({
     <div className="flex w-full items-center gap-2 sm:w-auto">
       <div className="min-w-0 flex-1 sm:w-44 sm:flex-none">{familyControl}</div>
       <Select
-        value={String(size.value)}
+        value={size.value === null ? "default" : String(size.value)}
         onValueChange={(next) => {
           if (typeof next !== "string") return;
+          if (next === "default") {
+            size.onClear?.();
+            return;
+          }
           const parsed = Number(next);
           if (Number.isInteger(parsed) && parsed >= size.min && parsed <= size.max) {
             size.onChange(parsed);
           }
         }}
       >
         <SelectTrigger size="sm" className="w-22 shrink-0" aria-label={size.label}>
-          <SelectValue>{size.value} px</SelectValue>
+          <SelectValue>{size.value === null ? "Default" : `${size.value} px`}</SelectValue>
         </SelectTrigger>
         <SelectPopup align="end" alignItemWithTrigger={false}>
+          {size.onClear !== undefined ? (
+            <SelectItem hideIndicator value="default">
+              Default
+            </SelectItem>
+          ) : null}
           {Array.from({ length: size.max - size.min + 1 }, (_, index) => size.min + index).map(
             (px) => (
               <SelectItem hideIndicator key={px} value={String(px)}>
 
@@ -172,8 +172,6 @@ export const MAX_CHAT_FONT_SIZE = 20;
 export const ChatFontSize = Schema.Int.check(
   Schema.isBetween({ minimum: MIN_CHAT_FONT_SIZE, maximum: MAX_CHAT_FONT_SIZE }),
 );
-export type ChatFontSize = typeof ChatFontSize.Type;
-export const DEFAULT_CHAT_FONT_SIZE: ChatFontSize = 14;
 
 export const MIN_CODE_FONT_SIZE = 10;
 export const MAX_CODE_FONT_SIZE = 18;
@@ -440,9 +438,8 @@ export const ClientSettingsSchema = Schema.Struct({
   fontSizePrompt: PromptFontSize.pipe(
     Schema.withDecodingDefault(Effect.succeed(DEFAULT_PROMPT_FONT_SIZE)),
   ),
-  fontSizeChat: ChatFontSize.pipe(
-    Schema.withDecodingDefault(Effect.succeed(DEFAULT_CHAT_FONT_SIZE)),
-  ),
+  // Null keeps messages on the interface size.
+  fontSizeChat: Schema.NullOr(ChatFontSize).pipe(Schema.withDecodingDefault(Effect.succeed(null))),
   fontSizeCode: CodeFontSize.pipe(
     Schema.withDecodingDefault(Effect.succeed(DEFAULT_CODE_FONT_SIZE)),
   ),
@@ -1762,7 +1759,7 @@ export const ClientSettingsPatch = Schema.Struct({
   onboardingCompletedAt: Schema.optionalKey(Schema.NullOr(Schema.String)),
   fontSizeInterface: Schema.optionalKey(InterfaceFontSize),
   fontSizePrompt: Schema.optionalKey(PromptFontSize),
-  fontSizeChat: Schema.optionalKey(ChatFontSize),
+  fontSizeChat: Schema.optionalKey(Schema.NullOr(ChatFontSize)),
   fontSizeCode: Schema.optionalKey(CodeFontSize),
   fontSizeTerminal: Schema.optionalKey(TerminalFontSize),
   fontFamilyChat: Schema.optionalKey(FontFamilyPreference),