diff --git a/cli.py b/cli.py
index a4ce0cdd56a..c1d5ada5562 100644
--- a/cli.py
+++ b/cli.py
@@ -77,14 +77,16 @@ except (ImportError, AttributeError):
 
 try:
     from hermes_cli.pt_input_extras import (
+        install_cmd_backspace_alias,
         install_ctrl_enter_alias,
         install_ignored_terminal_sequences,
         install_shift_enter_alias,
     )
     install_shift_enter_alias()
     install_ctrl_enter_alias()
+    install_cmd_backspace_alias()
     install_ignored_terminal_sequences()
-    del install_shift_enter_alias, install_ctrl_enter_alias, install_ignored_terminal_sequences
+    del install_shift_enter_alias, install_ctrl_enter_alias, install_cmd_backspace_alias, install_ignored_terminal_sequences
 except Exception:
     pass
 import threading
diff --git a/hermes_cli/pt_input_extras.py b/hermes_cli/pt_input_extras.py
index 16a0f17ea43..2efd5d8bc3b 100644
--- a/hermes_cli/pt_input_extras.py
+++ b/hermes_cli/pt_input_extras.py
@@ -83,6 +83,49 @@ def install_ctrl_enter_alias() -> int:
     return changed
 
 
+def install_cmd_backspace_alias() -> int:
+    """Map Cmd+Backspace / Cmd+ForwardDelete to the readline kill bindings
+    prompt_toolkit already ships (``unix-line-discard`` / ``kill-line``).
+
+    Terminals that rewrite Cmd+Backspace to Ctrl+U (``\\x15``) already work.
+    Kitty keyboard protocol and xterm modifyOtherKeys terminals instead
+    report Cmd as the *super* modifier bit (8), producing sequences
+    prompt_toolkit does not map — the raw bytes then fall through to
+    literal insertion.
+
+    Cmd+Backspace → ``Keys.ControlU`` (kill backward to start of line).
+    Codepoint 127 with modifier 9 (super) / 10 (super+shift):
+      - ``\\x1b[127;9u`` / ``\\x1b[127;10u``  — Kitty CSI-u
+      - ``\\x1b[27;9;127~``                   — xterm modifyOtherKeys
+
+    Cmd+ForwardDelete → ``Keys.ControlK`` (kill to end of line). The
+    forward-delete key is a CSI *tilde* key, not a CSI-u codepoint, so the
+    modifier rides in the standard ``CSI 3 ; mod ~`` form:
+      - ``\\x1b[3;9~`` / ``\\x1b[3;10~``
+
+    Returns the number of sequences whose mapping was changed.
+    """
+    try:
+        from prompt_toolkit.input.ansi_escape_sequences import ANSI_SEQUENCES
+        from prompt_toolkit.keys import Keys
+    except Exception:
+        return 0
+
+    aliases = {
+        "\x1b[127;9u": Keys.ControlU,
+        "\x1b[127;10u": Keys.ControlU,
+        "\x1b[27;9;127~": Keys.ControlU,
+        "\x1b[3;9~": Keys.ControlK,
+        "\x1b[3;10~": Keys.ControlK,
+    }
+    changed = 0
+    for seq, key in aliases.items():
+        if ANSI_SEQUENCES.get(seq) != key:
+            ANSI_SEQUENCES[seq] = key
+            changed += 1
+    return changed
+
+
 def install_ignored_terminal_sequences() -> int:
     """Map terminal-emitted noise sequences to ``Keys.Ignore`` so they
     are consumed by the VT100 parser before they reach key bindings or
diff --git a/tests/cli/test_cli_cmd_backspace.py b/tests/cli/test_cli_cmd_backspace.py
new file mode 100644
index 00000000000..d9ea60a6c6c
--- /dev/null
+++ b/tests/cli/test_cli_cmd_backspace.py
@@ -0,0 +1,79 @@
+"""Verify Cmd+Backspace / Cmd+ForwardDelete byte sequences from CSI-u
+terminals reach prompt_toolkit's readline kill bindings instead of leaking
+into the buffer as literal text.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from prompt_toolkit.input.ansi_escape_sequences import ANSI_SEQUENCES
+from prompt_toolkit.input.vt100_parser import Vt100Parser
+from prompt_toolkit.keys import Keys
+
+from hermes_cli.pt_input_extras import install_cmd_backspace_alias
+
+
+# Cmd rides as the super modifier bit (8), so modifier = 9 (super) or
+# 10 (super+shift).
+CMD_BACKSPACE_SEQUENCES = (
+    "\x1b[127;9u",       # Kitty CSI-u
+    "\x1b[127;10u",      # Kitty CSI-u, +shift
+    "\x1b[27;9;127~",    # xterm modifyOtherKeys
+)
+
+# Forward-delete is a CSI tilde key, not a CSI-u codepoint.
+CMD_FWD_DELETE_SEQUENCES = (
+    "\x1b[3;9~",
+    "\x1b[3;10~",
+)
+
+
+@pytest.fixture(autouse=True)
+def _ensure_alias_installed():
+    install_cmd_backspace_alias()
+
+
+def _parse(byte_seq: str):
+    out = []
+    parser = Vt100Parser(out.append)
+    for ch in byte_seq:
+        parser.feed(ch)
+    parser.flush()
+    return [kp.key for kp in out]
+
+
+@pytest.mark.parametrize("seq", CMD_BACKSPACE_SEQUENCES)
+def test_cmd_backspace_parses_as_ctrl_u(seq):
+    """Cmd+Backspace must reach unix-line-discard, exactly as Ctrl+U does."""
+    assert _parse(seq) == _parse("\x15")
+
+
+@pytest.mark.parametrize("seq", CMD_FWD_DELETE_SEQUENCES)
+def test_cmd_forward_delete_parses_as_ctrl_k(seq):
+    """Cmd+ForwardDelete must reach kill-line, exactly as Ctrl+K does."""
+    assert _parse(seq) == _parse("\x0b")
+
+
+@pytest.mark.parametrize("seq", CMD_BACKSPACE_SEQUENCES + CMD_FWD_DELETE_SEQUENCES)
+def test_sequences_emit_exactly_one_keypress(seq):
+    """The whole sequence is consumed. A partial match would emit Escape
+    plus the remainder as literal text — the bug this alias exists to fix."""
+    assert len(_parse(seq)) == 1
+
+
+def test_install_is_idempotent():
+    install_cmd_backspace_alias()
+    assert install_cmd_backspace_alias() == 0
+
+
+def test_unmodified_keys_keep_their_own_bindings():
+    """Aliasing the Cmd variants must not disturb the bare keys."""
+    assert ANSI_SEQUENCES["\x1b[3~"] == Keys.Delete
+    assert ANSI_SEQUENCES["\x7f"] == Keys.ControlH
+
+
+def test_ctrl_forward_delete_is_not_remapped():
+    """Ctrl+ForwardDelete (modifier 5) is delete-word on Linux/Windows and
+    must keep prompt_toolkit's own binding, not become kill-line."""
+    assert ANSI_SEQUENCES["\x1b[3;5~"] == Keys.ControlDelete
diff --git a/ui-tui/src/__tests__/textInputLineKill.test.ts b/ui-tui/src/__tests__/textInputLineKill.test.ts
new file mode 100644
index 00000000000..09c22f7466f
--- /dev/null
+++ b/ui-tui/src/__tests__/textInputLineKill.test.ts
@@ -0,0 +1,46 @@
+import { describe, expect, it } from 'vitest'
+
+import { isLineKillModifier } from '../components/textInput.js'
+
+// Cmd+Backspace should kill to the line boundary, but the modifier it is
+// distinguished by matters a great deal. `isActionMod` is the wrong test:
+//   - on macOS it accepts `key.meta`, and hermes-ink reports Option as
+//     `meta` — so Option+Backspace (delete-word, the macOS standard) would
+//     silently become "delete the whole line".
+//   - on Linux/Windows it is `key.ctrl`, and Ctrl+Backspace is delete-word
+//     there in readline, VS Code, browsers, and Windows Terminal.
+// Only the kitty CSI-u / modifyOtherKeys `super` bit means Cmd.
+
+const key = (over: Partial<{ ctrl: boolean; meta: boolean; super: boolean }> = {}) => ({
+  ctrl: false,
+  meta: false,
+  super: false,
+  ...over
+})
+
+describe('isLineKillModifier', () => {
+  it('accepts the super bit (Cmd via kitty CSI-u / modifyOtherKeys)', () => {
+    expect(isLineKillModifier(key({ super: true }))).toBe(true)
+  })
+
+  it('accepts super even when the terminal also sets a benign ctrl bit', () => {
+    // VS Code/Cursor forward Cmd chords as CSI-u with super + ctrl set.
+    expect(isLineKillModifier(key({ ctrl: true, super: true }))).toBe(true)
+  })
+
+  it('rejects meta so Option+Backspace stays delete-word on macOS', () => {
+    expect(isLineKillModifier(key({ meta: true }))).toBe(false)
+  })
+
+  it('rejects ctrl so Ctrl+Backspace stays delete-word on Linux/Windows', () => {
+    expect(isLineKillModifier(key({ ctrl: true }))).toBe(false)
+  })
+
+  it('rejects an unmodified keypress', () => {
+    expect(isLineKillModifier(key())).toBe(false)
+  })
+
+  it('treats a missing super field as absent rather than truthy', () => {
+    expect(isLineKillModifier({ ctrl: false, meta: false })).toBe(false)
+  })
+})
diff --git a/ui-tui/src/components/textInput.tsx b/ui-tui/src/components/textInput.tsx
index 9d35bbdf133..6fafe03b57b 100644
--- a/ui-tui/src/components/textInput.tsx
+++ b/ui-tui/src/components/textInput.tsx
@@ -321,6 +321,24 @@ export function resolveCursorLayout(display: string, cur: number, curRefCurrent:
   return cursorLayout(display, curRefCurrent, columns)
 }
 
+/**
+ * True when a Backspace / ForwardDelete keystroke should kill to the line
+ * boundary rather than delete a single word.
+ *
+ * Only the *super* bit qualifies. It is tempting to reuse `isActionMod`,
+ * but that accepts `key.meta` on macOS — and hermes-ink reports Option as
+ * `meta`, so Option+Backspace (delete-word, the macOS standard) would be
+ * swallowed. On Linux/Windows `isActionMod` is `key.ctrl`, and
+ * Ctrl+Backspace is delete-word there too. `super` is set only by kitty
+ * CSI-u / xterm modifyOtherKeys, where it unambiguously means Cmd.
+ *
+ * Terminals that instead rewrite Cmd+Backspace to Ctrl+U are handled by
+ * the `isMacActionFallback` kill-to-start path, not by this predicate.
+ */
+export function isLineKillModifier(key: { ctrl: boolean; meta: boolean; super?: boolean }): boolean {
+  return key.super === true
+}
+
 /**
  * Pure computation for the fast-echo backspace bypass: given the
  * current value/cursor (already validated by `canFastBackspaceShape`),
@@ -1198,7 +1216,12 @@ export function TextInput({
         v = v.slice(0, range.start) + v.slice(range.end)
         c = range.start
       } else if (k.backspace && c > 0) {
-        if (wordMod) {
+        if (isLineKillModifier(k)) {
+          // Cmd+Backspace — kill backward to start of line, matching the
+          // Ctrl+U (unix-line-discard) path below.
+          v = v.slice(c)
+          c = 0
+        } else if (wordMod) {
           const t = wordLeft(v, c)
           v = v.slice(0, t) + v.slice(c)
           c = t
@@ -1222,7 +1245,10 @@ export function TextInput({
           c = t
         }
       } else if (delFwd && c < v.length) {
-        if (wordMod) {
+        if (isLineKillModifier(k)) {
+          // Cmd+ForwardDelete — kill to end of line, matching Ctrl+K.
+          v = v.slice(0, c)
+        } else if (wordMod) {
           const t = wordRight(v, c)
           v = v.slice(0, c) + v.slice(t)
         } else {