diff --git a/apps/web/src/components/chat/ChatComposer.tsx b/apps/web/src/components/chat/ChatComposer.tsx
index bff16c88bbcc..331a764b1fbf 100644
--- a/apps/web/src/components/chat/ChatComposer.tsx
+++ b/apps/web/src/components/chat/ChatComposer.tsx
@@ -50,6 +50,7 @@ import {
   type ComposerSubmissionIntent,
   type ComposerTrigger,
   collapseExpandedComposerCursor,
+  composerEnterCommandAction,
   composerSubmissionIntentForEnter,
   detectComposerTrigger,
   expandCollapsedComposerCursor,
@@ -3048,12 +3049,13 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
   const submitCitationAndSend = useCallback(() => {
     const intent = composerSubmissionIntentForEnter({
       isMobileViewport,
+      sendKey: settings.composerSendKey,
       shiftKey: false,
       modifierKey: true,
       isDraftThread: routeKind === "draft",
     });
     submitComposer(undefined, intent ?? "foreground");
-  }, [isMobileViewport, routeKind, submitComposer]);
+  }, [isMobileViewport, routeKind, settings.composerSendKey, submitComposer]);
   const compactThreadContext = useCallback(() => {
     if (
       compactDisabled ||
@@ -3220,9 +3222,9 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
     }
     const { trigger } = resolveActiveComposerTrigger();
     const menuIsActive = composerMenuOpenRef.current || trigger !== null;
+    const currentItems = composerMenuItemsRef.current;
+    const selectedItem = activeComposerMenuItemRef.current ?? currentItems[0];
     if (menuIsActive) {
-      const currentItems = composerMenuItemsRef.current;
-      const selectedItem = activeComposerMenuItemRef.current ?? currentItems[0];
       if (key === "ArrowDown" && currentItems.length > 0) {
         nudgeComposerMenuHighlight("ArrowDown");
         return true;
@@ -3231,7 +3233,7 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
         nudgeComposerMenuHighlight("ArrowUp");
         return true;
       }
-      if ((key === "Enter" || key === "Tab") && selectedItem) {
+      if (key === "Tab" && selectedItem) {
         onSelectComposerItem(selectedItem);
         return true;
       }
@@ -3239,18 +3241,23 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
     if (key === "ArrowUp" || key === "ArrowDown") {
       return navigatePromptHistory(key === "ArrowUp" ? "backward" : "forward", event);
     }
-    const submissionIntent =
-      key === "Enter"
-        ? composerSubmissionIntentForEnter({
-            isMobileViewport,
-            shiftKey: event.shiftKey,
-            modifierKey: event.metaKey || event.ctrlKey,
-            isDraftThread: routeKind === "draft",
-          })
-        : null;
-    if (submissionIntent) {
-      submitComposer(undefined, submissionIntent);
-      return true;
+    if (key === "Enter") {
+      const action = composerEnterCommandAction({
+        menuCanSelect: menuIsActive && selectedItem != null,
+        isMobileViewport,
+        sendKey: settings.composerSendKey,
+        shiftKey: event.shiftKey,
+        modifierKey: event.metaKey || event.ctrlKey,
+        isDraftThread: routeKind === "draft",
+      });
+      if (action?.kind === "submit") {
+        submitComposer(undefined, action.intent);
+        return true;
+      }
+      if (action?.kind === "select-menu" && selectedItem) {
+        onSelectComposerItem(selectedItem);
+        return true;
+      }
     }
     return false;
   };
diff --git a/apps/web/src/components/settings/SettingsPanels.tsx b/apps/web/src/components/settings/SettingsPanels.tsx
index 4c108b01d0c8..0666d1e17653 100644
--- a/apps/web/src/components/settings/SettingsPanels.tsx
+++ b/apps/web/src/components/settings/SettingsPanels.tsx
@@ -168,6 +168,13 @@ const ENVIRONMENT_IDENTIFICATION_LABELS: Record<EnvironmentIdentificationMode, s
   none: "None",
 };
 
+const MOD_KEY_LABEL = isMacPlatform(navigator.platform) ? "Cmd" : "Ctrl";
+
+const COMPOSER_SEND_KEY_LABELS = {
+  enter: "Enter",
+  "mod-enter": `${MOD_KEY_LABEL}+Enter`,
+} as const;
+
 const TIMESTAMP_FORMAT_LABELS = {
   locale: "System default",
   "12-hour": "12-hour",
@@ -545,6 +552,9 @@ export function useSettingsRestore(onRestored?: () => void) {
       ...(settings.composerCollapseOnScroll !== DEFAULT_UNIFIED_SETTINGS.composerCollapseOnScroll
         ? ["Collapse composer on scroll"]
         : []),
+      ...(settings.composerSendKey !== DEFAULT_UNIFIED_SETTINGS.composerSendKey
+        ? ["Send prompt with"]
+        : []),
       ...(settings.contextWindowMeterEnabled !== DEFAULT_UNIFIED_SETTINGS.contextWindowMeterEnabled
         ? ["Context window indicator"]
         : []),
@@ -603,6 +613,7 @@ export function useSettingsRestore(onRestored?: () => void) {
       settings.confirmThreadDelete,
       settings.confirmThreadUnpin,
       settings.composerCollapseOnScroll,
+      settings.composerSendKey,
       settings.addProjectBaseDirectory,
       settings.defaultThreadEnvMode,
       settings.newWorktreesStartFromOrigin,
@@ -708,6 +719,7 @@ export function useSettingsRestore(onRestored?: () => void) {
       proactivePanelsEnabled: DEFAULT_UNIFIED_SETTINGS.proactivePanelsEnabled,
       showSkillsInSlashMenu: DEFAULT_UNIFIED_SETTINGS.showSkillsInSlashMenu,
       composerCollapseOnScroll: DEFAULT_UNIFIED_SETTINGS.composerCollapseOnScroll,
+      composerSendKey: DEFAULT_UNIFIED_SETTINGS.composerSendKey,
       contextWindowMeterEnabled: DEFAULT_UNIFIED_SETTINGS.contextWindowMeterEnabled,
       environmentIdentificationMode: DEFAULT_UNIFIED_SETTINGS.environmentIdentificationMode,
       glassOpacity: DEFAULT_UNIFIED_SETTINGS.glassOpacity,
@@ -2370,6 +2382,43 @@ export function GeneralSettingsPanel() {
           }
         />
 
+        <SettingsRow
+          {...searchableSetting("composer-send-key")}
+          description={`Set the prompt sending key to ${MOD_KEY_LABEL}+Enter to keep a stray Enter from sending an unfinished prompt.`}
+          resetAction={
+            settings.composerSendKey !== DEFAULT_UNIFIED_SETTINGS.composerSendKey ? (
+              <SettingResetButton
+                label="send prompt with"
+                onClick={() =>
+                  updateSettings({ composerSendKey: DEFAULT_UNIFIED_SETTINGS.composerSendKey })
+                }
+              />
+            ) : null
+          }
+          control={
+            <Select
+              value={settings.composerSendKey}
+              onValueChange={(value) => {
+                if (value) {
+                  updateSettings({ composerSendKey: value });
+                }
+              }}
+            >
+              <SelectTrigger size="sm" className="w-full sm:w-40" aria-label="Send prompt with">
+                <SelectValue>{COMPOSER_SEND_KEY_LABELS[settings.composerSendKey]}</SelectValue>
+              </SelectTrigger>
+              <SelectPopup align="end" alignItemWithTrigger={false}>
+                <SelectItem hideIndicator value="enter">
+                  {COMPOSER_SEND_KEY_LABELS.enter}
+                </SelectItem>
+                <SelectItem hideIndicator value="mod-enter">
+                  {COMPOSER_SEND_KEY_LABELS["mod-enter"]}
+                </SelectItem>
+              </SelectPopup>
+            </Select>
+          }
+        />
+
         <SettingsRow
           serverScoped
           {...searchableSetting("provider-update-checks")}
diff --git a/apps/web/src/components/settings/settingsSearch.ts b/apps/web/src/components/settings/settingsSearch.ts
index e32baf6f3987..356cb63a1a2b 100644
--- a/apps/web/src/components/settings/settingsSearch.ts
+++ b/apps/web/src/components/settings/settingsSearch.ts
@@ -220,6 +220,14 @@ export const SETTINGS_SEARCH_ITEMS = [
     to: "/settings/general",
     searchTerms: ["composer rest resting scroll wheel conversation timeline shrink minimize"],
   },
+  {
+    id: "composer-send-key",
+    title: "Send prompt with",
+    to: "/settings/general",
+    searchTerms: [
+      "enter cmd command ctrl control return submit accidental keyboard shortcut composer",
+    ],
+  },
   {
     id: "provider-update-checks",
     title: "Provider update checks",
diff --git a/apps/web/src/composer-logic.test.ts b/apps/web/src/composer-logic.test.ts
index cbc1821b0da0..232aae2a6a18 100644
--- a/apps/web/src/composer-logic.test.ts
+++ b/apps/web/src/composer-logic.test.ts
@@ -9,6 +9,7 @@ import { describe, expect, it } from "vite-plus/test";
 import {
   clampCollapsedComposerCursor,
   collapseExpandedComposerCursor,
+  composerEnterCommandAction,
   composerSubmissionIntentForEnter,
   detectComposerTrigger,
   expandCollapsedComposerCursor,
@@ -53,13 +54,15 @@ describe("formatAssistantCitationForComposer", () => {
 });
 
 describe("composerSubmissionIntentForEnter", () => {
+  const desktop = { isMobileViewport: false, isDraftThread: true } as const;
+
   it("submits plain Enter on desktop", () => {
     expect(
       composerSubmissionIntentForEnter({
-        isMobileViewport: false,
+        ...desktop,
+        sendKey: "enter",
         shiftKey: false,
         modifierKey: false,
-        isDraftThread: true,
       }),
     ).toBe("foreground");
   });
@@ -67,10 +70,11 @@ describe("composerSubmissionIntentForEnter", () => {
   it("inserts a newline for plain Enter on mobile", () => {
     expect(
       composerSubmissionIntentForEnter({
+        ...desktop,
         isMobileViewport: true,
+        sendKey: "enter",
         shiftKey: false,
         modifierKey: false,
-        isDraftThread: true,
       }),
     ).toBeNull();
   });
@@ -78,10 +82,10 @@ describe("composerSubmissionIntentForEnter", () => {
   it("inserts a newline for Shift+Enter", () => {
     expect(
       composerSubmissionIntentForEnter({
-        isMobileViewport: false,
+        ...desktop,
+        sendKey: "enter",
         shiftKey: true,
         modifierKey: false,
-        isDraftThread: true,
       }),
     ).toBeNull();
   });
@@ -89,10 +93,10 @@ describe("composerSubmissionIntentForEnter", () => {
   it("submits a new thread in the background with Mod+Enter", () => {
     expect(
       composerSubmissionIntentForEnter({
-        isMobileViewport: false,
+        ...desktop,
+        sendKey: "enter",
         shiftKey: false,
         modifierKey: true,
-        isDraftThread: true,
       }),
     ).toBe("background");
   });
@@ -100,13 +104,125 @@ describe("composerSubmissionIntentForEnter", () => {
   it("keeps Mod+Enter in the foreground for an active thread", () => {
     expect(
       composerSubmissionIntentForEnter({
-        isMobileViewport: false,
+        ...desktop,
+        isDraftThread: false,
+        sendKey: "enter",
         shiftKey: false,
         modifierKey: true,
-        isDraftThread: false,
       }),
     ).toBe("foreground");
   });
+
+  describe("with Mod+Enter as the send key", () => {
+    it.each([
+      ["plain Enter", false],
+      ["Shift+Enter", true],
+    ])("inserts a newline for %s", (_label, shiftKey) => {
+      expect(
+        composerSubmissionIntentForEnter({
+          ...desktop,
+          sendKey: "mod-enter",
+          shiftKey,
+          modifierKey: false,
+        }),
+      ).toBeNull();
+    });
+
+    it("submits a draft in the foreground with Mod+Enter", () => {
+      expect(
+        composerSubmissionIntentForEnter({
+          ...desktop,
+          sendKey: "mod-enter",
+          shiftKey: false,
+          modifierKey: true,
+        }),
+      ).toBe("foreground");
+    });
+
+    it("moves the background start to Shift+Mod+Enter", () => {
+      expect(
+        composerSubmissionIntentForEnter({
+          ...desktop,
+          sendKey: "mod-enter",
+          shiftKey: true,
+          modifierKey: true,
+        }),
+      ).toBe("background");
+      expect(
+        composerSubmissionIntentForEnter({
+          ...desktop,
+          isDraftThread: false,
+          sendKey: "mod-enter",
+          shiftKey: true,
+          modifierKey: true,
+        }),
+      ).toBe("foreground");
+    });
+  });
+});
+
+describe("composerEnterCommandAction", () => {
+  const desktop = { isMobileViewport: false, isDraftThread: true } as const;
+
+  it("lets the completion menu consume unmodified Enter", () => {
+    expect(
+      composerEnterCommandAction({
+        ...desktop,
+        menuCanSelect: true,
+        sendKey: "enter",
+        shiftKey: false,
+        modifierKey: false,
+      }),
+    ).toEqual({ kind: "select-menu" });
+  });
+
+  it("sends with Mod+Enter even when the completion menu is open", () => {
+    expect(
+      composerEnterCommandAction({
+        ...desktop,
+        menuCanSelect: true,
+        sendKey: "mod-enter",
+        shiftKey: false,
+        modifierKey: true,
+      }),
+    ).toEqual({ kind: "submit", intent: "foreground" });
+  });
+
+  it("starts a background draft with Shift+Mod+Enter while the menu is open", () => {
+    expect(
+      composerEnterCommandAction({
+        ...desktop,
+        menuCanSelect: true,
+        sendKey: "mod-enter",
+        shiftKey: true,
+        modifierKey: true,
+      }),
+    ).toEqual({ kind: "submit", intent: "background" });
+  });
+
+  it("still lets the menu consume Enter when send is Mod+Enter", () => {
+    expect(
+      composerEnterCommandAction({
+        ...desktop,
+        menuCanSelect: true,
+        sendKey: "mod-enter",
+        shiftKey: false,
+        modifierKey: false,
+      }),
+    ).toEqual({ kind: "select-menu" });
+  });
+
+  it("submits Mod+Enter as a background draft when send is Enter", () => {
+    expect(
+      composerEnterCommandAction({
+        ...desktop,
+        menuCanSelect: true,
+        sendKey: "enter",
+        shiftKey: false,
+        modifierKey: true,
+      }),
+    ).toEqual({ kind: "submit", intent: "background" });
+  });
 });
 
 describe("detectComposerTrigger", () => {
diff --git a/apps/web/src/composer-logic.ts b/apps/web/src/composer-logic.ts
index 4a5b7022adc7..5e701366af22 100644
--- a/apps/web/src/composer-logic.ts
+++ b/apps/web/src/composer-logic.ts
@@ -1,4 +1,4 @@
-import type { AssistantCitation } from "@t3tools/contracts";
+import type { AssistantCitation, ComposerSendKey } from "@t3tools/contracts";
 import {
   serializeAssistantCitation,
   withAssistantCitationComment,
@@ -26,14 +26,49 @@ export function formatAssistantCitationForComposer(citation: AssistantCitation,
 
 export function composerSubmissionIntentForEnter(input: {
   isMobileViewport: boolean;
+  sendKey: ComposerSendKey;
   shiftKey: boolean;
   modifierKey: boolean;
   isDraftThread: boolean;
 }): ComposerSubmissionIntent | null {
-  if (input.isMobileViewport || input.shiftKey) {
+  if (input.isMobileViewport) {
     return null;
   }
-  return input.modifierKey && input.isDraftThread ? "background" : "foreground";
+  const { sendKey, shiftKey, modifierKey } = input;
+  const sends = sendKey === "mod-enter" ? modifierKey : !shiftKey;
+  if (!sends) {
+    return null;
+  }
+  // Mod+Enter starts a draft in the background; when it is the send key itself,
+  // Shift+Mod+Enter takes over that role.
+  const background = sendKey === "mod-enter" ? modifierKey && shiftKey : modifierKey;
+  return background && input.isDraftThread ? "background" : "foreground";
+}
+
+export type ComposerEnterCommandAction =
+  | { kind: "submit"; intent: ComposerSubmissionIntent }
+  | { kind: "select-menu" };
+
+/** Unmodified Enter confirms a completion. Modified Enter is a send chord. */
+export function composerEnterCommandAction(input: {
+  menuCanSelect: boolean;
+  isMobileViewport: boolean;
+  sendKey: ComposerSendKey;
+  shiftKey: boolean;
+  modifierKey: boolean;
+  isDraftThread: boolean;
+}): ComposerEnterCommandAction | null {
+  const intent = composerSubmissionIntentForEnter(input);
+  if (intent && input.modifierKey) {
+    return { kind: "submit", intent };
+  }
+  if (input.menuCanSelect) {
+    return { kind: "select-menu" };
+  }
+  if (intent) {
+    return { kind: "submit", intent };
+  }
+  return null;
 }
 
 const isInlineTokenSegment = (segment: ComposerPromptSegment): boolean => segment.type !== "text";
diff --git a/docs/user/composer.md b/docs/user/composer.md
index 4a8df5333664..241b0f50904c 100644
--- a/docs/user/composer.md
+++ b/docs/user/composer.md
@@ -56,6 +56,14 @@ is unavailable or has changed, the saved quote remains readable.
 Mobile displays saved quotes and comments, but does not create citations or
 navigate to their sources.
 
+## Require Cmd/Ctrl+Enter to send
+
+On web and desktop, Enter sends the prompt and Shift+Enter starts a new line. If
+you keep sending drafts early, switch Settings → General → Behavior →
+**Send prompt with** to `Cmd+Enter` on macOS or `Ctrl+Enter` on Windows and
+Linux. Enter then starts a new line, and `Shift+Cmd+Enter` on macOS or
+`Shift+Ctrl+Enter` on Windows and Linux starts a new thread in the background.
+
 ## Recall a sent prompt
 
 Press `ArrowUp` in an empty composer to bring back the last prompt you sent in this thread. Press
diff --git a/docs/user/thread-sidebar.md b/docs/user/thread-sidebar.md
index b2c244a6123e..076676cfc33c 100644
--- a/docs/user/thread-sidebar.md
+++ b/docs/user/thread-sidebar.md
@@ -18,7 +18,8 @@ if that project exists there. Otherwise it selects an environment that has it.
 In a desktop browser or the desktop app, press `Cmd+Enter` on macOS or `Ctrl+Enter`
 on Windows and Linux to start a new thread and immediately open another draft. The
 next draft keeps the workspace mode and base branch you selected. With **New
-worktree**, each background submission creates its own worktree.
+worktree**, each background submission creates its own worktree. If `Cmd+Enter`
+is your send key, hold Shift as well.
 
 ## Pin and reorder threads
 
diff --git a/packages/contracts/src/settings.ts b/packages/contracts/src/settings.ts
index 3491103da94f..394dd54e46e6 100644
--- a/packages/contracts/src/settings.ts
+++ b/packages/contracts/src/settings.ts
@@ -44,6 +44,11 @@ export const DiffLayout = Schema.Literals(["stacked", "split"]);
 export type DiffLayout = typeof DiffLayout.Type;
 const DEFAULT_DIFF_LAYOUT: DiffLayout = "stacked";
 
+// Which Enter chord sends the composer prompt. "mod" is Cmd on macOS and Ctrl elsewhere.
+export const ComposerSendKey = Schema.Literals(["enter", "mod-enter"]);
+export type ComposerSendKey = typeof ComposerSendKey.Type;
+const DEFAULT_COMPOSER_SEND_KEY: ComposerSendKey = "enter";
+
 export const SidebarProjectSortOrder = Schema.Literals(["updated_at", "created_at", "manual"]);
 export type SidebarProjectSortOrder = typeof SidebarProjectSortOrder.Type;
 export const DEFAULT_SIDEBAR_PROJECT_SORT_ORDER: SidebarProjectSortOrder = "updated_at";
@@ -406,6 +411,9 @@ export const ClientSettingsSchema = Schema.Struct({
   // Desktop resting composer: scrolling an existing thread's conversation
   // settles the composer into its single-line layout. Losing focus never does.
   composerCollapseOnScroll: Schema.Boolean.pipe(Schema.withDecodingDefault(Effect.succeed(true))),
+  composerSendKey: ComposerSendKey.pipe(
+    Schema.withDecodingDefault(Effect.succeed(DEFAULT_COMPOSER_SEND_KEY)),
+  ),
   proactivePanelsEnabled: Schema.Boolean.pipe(Schema.withDecodingDefault(Effect.succeed(false))),
   showSkillsInSlashMenu: Schema.Boolean.pipe(Schema.withDecodingDefault(Effect.succeed(true))),
   // Legacy sidebar (the original per-project tree). Deliberately a fresh key
@@ -1352,6 +1360,7 @@ export const ClientSettingsPatch = Schema.Struct({
   planModeEnabled: Schema.optionalKey(Schema.Boolean),
   contextWindowMeterEnabled: Schema.optionalKey(Schema.Boolean),
   composerCollapseOnScroll: Schema.optionalKey(Schema.Boolean),
+  composerSendKey: Schema.optionalKey(ComposerSendKey),
   proactivePanelsEnabled: Schema.optionalKey(Schema.Boolean),
   showSkillsInSlashMenu: Schema.optionalKey(Schema.Boolean),
   legacySidebarEnabled: Schema.optionalKey(Schema.Boolean),