Detection, done like sync:

- ESC[?u goes to every VT100-like terminal at attach, whatever the
  options.
- A reply turns on a new kittykeys terminal feature. Users can force
  it on or off with terminal-features kittykeys, including kittykeys@
  to turn it off.
- Changing extended-keys now takes effect immediately for attached
  clients (options.c).

Use, per client, when extended-keys is on: Kitty for clients that have
kittykeys, modifyOtherKeys for clients with extkeys, VT10x otherwise.

Pane side:

- Applications can request either protocol; Kitty wins if one asks for
  both.
- Each application gets what it asked for, whichever client typed the
  key.
- ESC[?u is answered truthfully.
- The per-client gate is gone. window.c and popup.c are simply
  master's versions again.

extended-keys always is back to its master meaning, forcing
modifyOtherKeys mode 1 only. Forcing Kitty on every program would have
sent bash ESC[97;5u for Ctrl-A.

extended-keys-format kitty is still accepted, but now behaves the same
as csi-u.

CHANGES

@@ -111,14 +111,14 @@ CHANGES FROM 3.7c TO 3.8
 
 * Change show-options and show-hooks to use formats and add a -F flag to each.
 
-* Add support for the Kitty keyboard protocol, selected with a new kitty
-  value for the extended-keys-format option. This can report the Super and
-  Hyper modifiers (key name prefixes s- and H-) as well as Control, Meta
-  and Shift. The protocol is negotiated separately with each client, so
-  terminals with different capabilities may be attached at the same time;
-  clients without it use standard extended keys, or VT10x keys if those
-  are also unavailable, and their input is translated for applications
-  which have asked for Kitty encoding.
+* Add support for the Kitty keyboard protocol. When extended-keys is on,
+  tmux uses it with terminals which support it, detected when a client
+  attaches or set with a new kittykeys terminal feature, and standard
+  extended keys or VT10x keys with other terminals, so terminals with
+  different capabilities may be attached at the same time. Programs inside
+  tmux may ask for either the Kitty protocol or modifyOtherKeys and get keys
+  in the form they asked for. The Kitty protocol can report the Super and
+  Hyper modifiers (key name prefixes s- and H-).
 
 * Add a client_key_mode format giving the extended key reporting mode in
   use for a client, alongside the existing pane_key_mode for a pane.

format.c

@@ -1635,11 +1635,9 @@ format_cb_client_key_mode(struct format_tree *ft)
 	}
 
 	/* This mirrors the choice made in tty_update_features(). */
-	kitty = ((c->tty.flags & (TTY_HAVEKKB|TTY_KKBSUPPORT)) ==
-	    (TTY_HAVEKKB|TTY_KKBSUPPORT));
+	kitty = ((c->tty.term->flags & TERM_KITTYKEYS) != 0);
 	eks = (options_get_number(global_options, "extended-keys") != 0);
-	if (kitty && options_get_number(global_options,
-	    "extended-keys-format") == EXTENDED_KEYS_KITTY)
+	if (kitty)
 		eks = 0;
 	if (eks && tty_term_has(c->tty.term, TTYC_ENEKS))
 		mode = "Ext";
@@ -2527,10 +2525,7 @@ format_cb_pane_key_mode(struct format_tree *ft)
 	char	*s;
 
 	if (ft->wp != NULL && ft->wp->screen != NULL) {
-		if (options_get_number(global_options, "extended-keys-format") ==
-		    EXTENDED_KEYS_KITTY) {
-			if (ft->wp->screen->kitty_keys.flags == 0)
-				return (xstrdup("VT10x"));
+		if (ft->wp->screen->kitty_keys.flags != 0) {
 			xasprintf(&s, "Kitty %u",
 			    ft->wp->screen->kitty_keys.flags);
 			return (s);

input-keys.c

@@ -395,8 +395,7 @@ input_key_build(void)
 
 /* Translate a key code into an output key sequence for a pane. */
 int
-input_key_pane(struct window_pane *wp, key_code key, struct mouse_event *m,
-    int extended_encoding)
+input_key_pane(struct window_pane *wp, key_code key, struct mouse_event *m)
 {
 	if (log_get_level() != 0) {
 		log_debug("writing key 0x%llx (%s) to %%%u", key,
@@ -408,20 +407,7 @@ input_key_pane(struct window_pane *wp, key_code key, struct mouse_event *m,
 			input_key_mouse(wp, m);
 		return (0);
 	}
-	return (input_key(wp->screen, wp->event, key, extended_encoding));
-}
-
-/* Return whether a key may use the configured extended encoding. */
-int
-input_key_client_supports_extended(struct client *c, key_code key)
-{
-	if (c == NULL || (key & KEYC_SENT))
-		return (1);
-	if (options_get_number(global_options, "extended-keys") == 0)
-		return (0);
-	if (c->tty.flags & TTY_KKBPUSHED)
-		return (1);
-	return (tty_term_has(c->tty.term, TTYC_ENEKS));
+	return (input_key(wp->screen, wp->event, key));
 }
 
 static void
@@ -586,8 +572,7 @@ input_key_mode1(struct bufferevent *bev, key_code key)
 
 /* Translate a key code into an output key sequence. */
 int
-input_key(struct screen *s, struct bufferevent *bev, key_code key,
-    int extended_encoding)
+input_key(struct screen *s, struct bufferevent *bev, key_code key)
 {
 	struct input_key_entry	*ike = NULL;
 	key_code		 newkey;
@@ -604,9 +589,8 @@ input_key(struct screen *s, struct bufferevent *bev, key_code key,
 		return (0);
 	}
 
-	if (extended_encoding &&
-	    options_get_number(global_options, "extended-keys-format") ==
-	    EXTENDED_KEYS_KITTY && input_key_kitty(s, bev, key) == 0)
+	/* Kitty keys take precedence if the application asked for them. */
+	if (input_key_kitty(s, bev, key) == 0)
 		return (0);
 
 	/* Is this backspace? */
@@ -700,8 +684,7 @@ input_key(struct screen *s, struct bufferevent *bev, key_code key,
 	}
 	if (key & (KEYC_SUPER|KEYC_HYPER))
 		return (input_key_vt10x(bev, key));
-	if (options_get_number(global_options, "extended-keys-format") ==
-	    EXTENDED_KEYS_KITTY)
+	if (s->kitty_keys.flags & KITTY_KEY_SUPPORTED)
 		return (input_key_vt10x(bev, key));
 
 	/*

input-kitty.c

@@ -145,21 +145,10 @@ static const struct input_kitty_key input_kitty_keys[] = {
 	{ KEYC_ISO_LEVEL5_SHIFT, 57454, 'u' }
 };
 
-static u_int
-input_kitty_default_flags(void)
-{
-	if (options_get_number(global_options, "extended-keys") == 2 &&
-	    options_get_number(global_options, "extended-keys-format") ==
-	    EXTENDED_KEYS_KITTY)
-		return (KITTY_KEY_DISAMBIGUATE);
-	return (0);
-}
-
 void
 input_kitty_reset(struct screen *s)
 {
 	memset(&s->kitty_keys, 0, sizeof s->kitty_keys);
-	s->kitty_keys.flags = input_kitty_default_flags();
 }
 
 void
@@ -186,7 +175,6 @@ input_kitty_set(struct screen *s, u_int flags, int mode)
 		s->kitty_keys.flags &= ~flags;
 	else
 		s->kitty_keys.flags = flags;
-	s->kitty_keys.flags |= input_kitty_default_flags();
 }
 
 void
@@ -194,8 +182,7 @@ input_kitty_push(struct screen *s, u_int flags)
 {
 	s->kitty_keys.saved_flags = s->kitty_keys.flags;
 	s->kitty_keys.have_saved = 1;
-	s->kitty_keys.flags = (flags & KITTY_KEY_SUPPORTED)|
-	    input_kitty_default_flags();
+	s->kitty_keys.flags = flags & KITTY_KEY_SUPPORTED;
 }
 
 void
@@ -206,9 +193,8 @@ input_kitty_pop(struct screen *s, u_int count)
 	if (s->kitty_keys.have_saved && count == 1)
 		s->kitty_keys.flags = s->kitty_keys.saved_flags;
 	else
-		s->kitty_keys.flags = input_kitty_default_flags();
+		s->kitty_keys.flags = 0;
 	s->kitty_keys.have_saved = 0;
-	s->kitty_keys.flags |= input_kitty_default_flags();
 }
 
 static u_int

input.c

@@ -162,7 +162,6 @@ static void	input_set_state(struct input_ctx *,
 		    const struct input_transition *);
 static void	input_reset_cell(struct input_ctx *);
 static void	input_report_current_theme(struct input_ctx *);
-static int	input_pane_supports_extended(struct window_pane *);
 static void	input_osc_4(struct input_ctx *, const char *);
 static void	input_osc_8(struct input_ctx *, const char *);
 static void	input_osc_9(struct input_ctx *, const char *);
@@ -1180,29 +1179,6 @@ input_send_reply(struct input_ctx *ictx, const char *reply)
 	}
 }
 
-/* Return whether attached tty clients can provide extended keys to a pane. */
-static int
-input_pane_supports_extended(struct window_pane *wp)
-{
-	struct client	*c;
-
-	if (wp == NULL)
-		return (1);
-	TAILQ_FOREACH(c, &clients, entry) {
-		if ((c->flags & (CLIENT_TERMINAL|CLIENT_ATTACHED)) !=
-		    (CLIENT_TERMINAL|CLIENT_ATTACHED))
-			continue;
-		if (c->flags &
-		    (CLIENT_UNATTACHEDFLAGS|CLIENT_CONTROL|CLIENT_READONLY))
-			continue;
-		if (c->session == NULL || !session_has(c->session, wp->window))
-			continue;
-		if (!input_key_client_supports_extended(c, 0))
-			return (0);
-	}
-	return (1);
-}
-
 /* Reply to terminal query. */
 static void printflike(3, 4)
 input_reply(struct input_ctx *ictx, int add, const char *fmt, ...)
@@ -1557,9 +1533,6 @@ input_csi_dispatch(struct input_ctx *ictx)
 			screen_write_cursormove(sctx, m - 1, n - 1, 1);
 		break;
 	case INPUT_CSI_MODSET:
-		if (options_get_number(global_options, "extended-keys-format") ==
-		    EXTENDED_KEYS_KITTY)
-			break;
 		n = input_get(ictx, 0, 0, 0);
 		if (n != 4)
 			break;
@@ -1579,9 +1552,6 @@ input_csi_dispatch(struct input_ctx *ictx)
 			screen_write_mode_set(sctx, MODE_KEYS_EXTENDED);
 		break;
 	case INPUT_CSI_MODOFF:
-		if (options_get_number(global_options, "extended-keys-format") ==
-		    EXTENDED_KEYS_KITTY)
-			break;
 		n = input_get(ictx, 0, 0, 0);
 		if (n != 4)
 			break;
@@ -1596,19 +1566,12 @@ input_csi_dispatch(struct input_ctx *ictx)
 			screen_write_mode_set(sctx, MODE_KEYS_EXTENDED);
 		break;
 	case INPUT_CSI_KITTY_QUERY:
-		if (options_get_number(global_options, "extended-keys") == 0 ||
-		    options_get_number(global_options, "extended-keys-format") !=
-		    EXTENDED_KEYS_KITTY)
+		if (options_get_number(global_options, "extended-keys") == 0)
 			break;
-		n = s->kitty_keys.flags;
-		if (!input_pane_supports_extended(ictx->wp))
-			n = 0;
-		input_reply(ictx, 1, "\033[?%uu", n);
+		input_reply(ictx, 1, "\033[?%uu", s->kitty_keys.flags);
 		break;
 	case INPUT_CSI_KITTY_SET:
-		if (options_get_number(global_options, "extended-keys") == 0 ||
-		    options_get_number(global_options, "extended-keys-format") !=
-		    EXTENDED_KEYS_KITTY)
+		if (options_get_number(global_options, "extended-keys") == 0)
 			break;
 		n = input_get(ictx, 0, 0, 0);
 		m = input_get(ictx, 1, 1, 1);
@@ -1616,18 +1579,14 @@ input_csi_dispatch(struct input_ctx *ictx)
 			input_kitty_set(s, n, m);
 		break;
 	case INPUT_CSI_KITTY_PUSH:
-		if (options_get_number(global_options, "extended-keys") == 0 ||
-		    options_get_number(global_options, "extended-keys-format") !=
-		    EXTENDED_KEYS_KITTY)
+		if (options_get_number(global_options, "extended-keys") == 0)
 			break;
 		n = input_get(ictx, 0, 0, 0);
 		if (n >= 0)
 			input_kitty_push(s, n);
 		break;
 	case INPUT_CSI_KITTY_POP:
-		if (options_get_number(global_options, "extended-keys") == 0 ||
-		    options_get_number(global_options, "extended-keys-format") !=
-		    EXTENDED_KEYS_KITTY)
+		if (options_get_number(global_options, "extended-keys") == 0)
 			break;
 		n = input_get(ictx, 0, 1, 1);
 		if (n >= 0)

options.c

@@ -1400,6 +1400,12 @@ options_push_changes(const char *name)
 		TAILQ_FOREACH(loop, &clients, entry)
 			server_client_set_key_table(loop, NULL);
 	}
+	if (strcmp(name, "extended-keys") == 0) {
+		TAILQ_FOREACH(loop, &clients, entry) {
+			if (loop->tty.flags & TTY_STARTED)
+				tty_update_features(&loop->tty);
+		}
+	}
 	if (strcmp(name, "user-keys") == 0) {
 		TAILQ_FOREACH(loop, &clients, entry) {
 			if (loop->tty.flags & TTY_OPENED)

popup.c

@@ -449,8 +449,7 @@ popup_key_cb(struct client *c, void *data, struct key_event *event)
 			bufferevent_write(job_get_event(pd->job), buf, len);
 			return (0);
 		}
-		input_key(&pd->s, job_get_event(pd->job), event->key,
-		    input_key_client_supports_extended(pd->c, event->key));
+		input_key(&pd->s, job_get_event(pd->job), event->key);
 	}
 	return (0);
 

regress/kitty-keys-clients.sh

@@ -1,27 +1,23 @@
 #!/bin/sh
 
-# Test per-client keyboard protocol negotiation and pane-side fallback.
+# Test per-client keyboard protocol detection and pane-side encoding.
 
 PATH=/bin:/usr/bin
 TERM=screen
 
 [ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
 KCONF=$(mktemp)
-UCONF=$(mktemp)
 LCONF=$(mktemp)
 OUT=$(mktemp)
 TMP=$(mktemp)
 SOCKETS="testKmc$$ testKka$$ testKua$$ testKrt$$ testKru$$ testKlq$$ testKlu$$"
 
-printf '%s\n' 'set -g extended-keys on' \
-    'set -g extended-keys-format kitty' >"$KCONF"
-printf '%s\n' 'set -g extended-keys on' \
-    'set -g extended-keys-format csi-u' >"$UCONF"
+printf '%s\n' 'set -g extended-keys on' >"$KCONF"
 printf '%s\n' 'set -g extended-keys off' >"$LCONF"
 
 cleanup()
 {
-	rm -f "$KCONF" "$UCONF" "$LCONF" "$OUT" "$TMP"
+	rm -f "$KCONF" "$LCONF" "$OUT" "$TMP"
 	for socket in $SOCKETS; do
 		$TEST_TMUX -L"$socket" kill-server 2>/dev/null
 	done
@@ -78,16 +74,17 @@ wait_for_client_mode()
 	[ "$(client_mode "$tmux" "$session")" = "$wanted" ]
 }
 
-# A server preferring Kitty must negotiate each client independently.
+# Each client must be negotiated independently. A tmux with extended-keys off
+# stands in for a terminal without Kitty keys, since it does not answer the
+# query.
 M="$TEST_TMUX -LtestKmc$$ -f$KCONF"
 KA="$TEST_TMUX -LtestKka$$ -f$KCONF"
-UA="$TEST_TMUX -LtestKua$$ -f$UCONF"
+UA="$TEST_TMUX -LtestKua$$ -f$LCONF"
 $M new-session -d -x80 -y24 -s kitty || exit 1
 $M new-session -d -x80 -y24 -s csiu || exit 1
 $KA new-session -d -x80 -y24 "$M attach-session -t kitty" || exit 1
 $UA new-session -d -x80 -y24 "$M attach-session -t csiu" || exit 1
 wait_for_mode "$KA" 'Kitty 1' || exit 1
-wait_for_mode "$UA" 'Ext 2' || exit 1
 
 # Each client must report the protocol its own terminal negotiated.
 wait_for_client_mode "$M" kitty 'Kitty 1' || exit 1
@@ -99,7 +96,7 @@ uc=$($M list-clients -F '#{client_name} #{client_session}' |
 $M command-prompt -t"$uc" -k 'display-message -pl "%%"' >"$TMP" &
 pid=$!
 sleep 0.2
-$UA send-keys 'Escape [97;5u'
+$UA send-keys Escape '[97;5u'
 wait "$pid"
 [ "$(tr -d '[:space:]' <"$TMP")" = 'C-a' ] || exit 1
 
@@ -117,11 +114,10 @@ $M kill-server 2>/dev/null
 # Standard extended input must be translated for a Kitty-requesting pane.
 : >"$OUT"
 R="$TEST_TMUX -LtestKrt$$ -f$KCONF"
-RU="$TEST_TMUX -LtestKru$$ -f$UCONF"
+RU="$TEST_TMUX -LtestKru$$ -f$LCONF"
 $R new-session -d -x80 -y24 \
     "stty raw -echo; printf '\033[>1u'; dd bs=1 count=7 2>/dev/null | od -An -v -t x1 >'$OUT'; sleep 5" || exit 1
 $RU new-session -d -x80 -y24 "$R attach-session" || exit 1
-wait_for_mode "$RU" 'Ext 2' || exit 1
 wait_for_client_mode "$R" '' 'Ext' || exit 1
 $RU send-keys C-a
 wait_for_output "$OUT" || exit 1
@@ -129,16 +125,22 @@ wait_for_output "$OUT" || exit 1
 $RU kill-server 2>/dev/null
 $R kill-server 2>/dev/null
 
-# Do not report Kitty active when an attached client only supports VT10x.
+# An application is told the Kitty flags it asked for even when a client that
+# only supports VT10x is attached, and keys from that client are encoded as it
+# asked.
 : >"$OUT"
+: >"$TMP"
 printf '%s\n' "set -as terminal-overrides ',*:Eneks@:Dseks@'" >>"$KCONF"
 LQ="$TEST_TMUX -LtestKlq$$ -f$KCONF"
 LU="$TEST_TMUX -LtestKlu$$ -f$LCONF"
 $LQ new-session -d -x80 -y24 \
-    "stty raw -echo; sleep 2; printf '\033[>1u\033[?u'; dd bs=1 count=5 2>/dev/null | od -An -v -t x1 >'$OUT'; sleep 5" || exit 1
+    "stty raw -echo; sleep 2; printf '\033[>1u\033[?u'; dd bs=1 count=5 2>/dev/null | od -An -v -t x1 >'$OUT'; dd bs=1 count=7 2>/dev/null | od -An -v -t x1 >'$TMP'; sleep 5" || exit 1
 $LU new-session -d -x80 -y24 "$LQ attach-session" || exit 1
 wait_for_output "$OUT" || exit 1
-[ "$(tr -d ' \n' <"$OUT")" = '1b5b3f3075' ] || exit 1
+[ "$(tr -d ' \n' <"$OUT")" = '1b5b3f3175' ] || exit 1
 wait_for_client_mode "$LQ" '' 'VT10x' || exit 1
+$LU send-keys C-a
+wait_for_output "$TMP" || exit 1
+[ "$(tr -d ' \n' <"$TMP")" = '1b5b39373b3575' ] || exit 1
 
 exit 0

regress/kitty-keys-input.sh

@@ -12,8 +12,7 @@ TERM=screen
 CONF=$(mktemp)
 TMP=$(mktemp)
 
-printf '%s\n' 'set -g extended-keys on' \
-    'set -g extended-keys-format kitty' >"$CONF"
+printf '%s\n' 'set -g extended-keys on' >"$CONF"
 
 TMUX="$TEST_TMUX -LtestKIA$$ -f$CONF"
 TMUX2="$TEST_TMUX -LtestKIB$$ -f$CONF"
@@ -44,7 +43,9 @@ assert_key()
 
 	$TMUX2 command-prompt -k 'display-message -pl "%%"' >"$TMP" &
 	sleep 0.15
-	$TMUX send-keys $keys
+	# Send raw bytes so the outer tmux does not encode them itself.
+	raw=$(printf '%s' "$keys" | sed -e 's/Escape /\\033/g' -e 's/ //g')
+	$TMUX send-keys -H $(printf "$raw" | od -An -v -t x1)
 	wait
 
 	actual=$(tr -d '[:space:]' <"$TMP")
@@ -62,10 +63,6 @@ if ! wait_for_mode 'Kitty 1'; then
 	exit 1
 fi
 
-# The handshake is done, so stop the outer tmux encoding the raw sequences
-# below as Kitty keys itself.
-$TMUX set-option -g extended-keys-format csi-u
-
 # Modifiers, including the Kitty-only Super and Hyper.
 assert_key 'Escape [97;2u' 'S-a'
 assert_key 'Escape [97;3u' 'M-a'

regress/kitty-keys.sh

@@ -13,8 +13,7 @@ TMUX="$TEST_TMUX -LtestK$$ -f$CONF"
 
 trap 'rm -f "$CONF" "$OUT"; $TMUX kill-server 2>/dev/null' 0 1 15
 
-printf '%s\n' 'set -g extended-keys on' \
-    'set -g extended-keys-format kitty' >"$CONF"
+printf '%s\n' 'set -g extended-keys on' >"$CONF"
 
 wait_for_output()
 {
@@ -90,11 +89,13 @@ wait_for_output
 check_output 1b5b3f31751b5b3f3075
 
 : >"$OUT"
+# "always" forces modifyOtherKeys mode 1, not Kitty keys.
 $TMUX set-option -g extended-keys always
 $TMUX respawn-pane -k -t: \
     "stty raw -echo; printf '\033[>0u\033[?u'; dd bs=1 count=5 2>/dev/null | od -An -v -t x1 >'$OUT'; sleep 5"
 wait_for_output
-check_output 1b5b3f3175
+check_output 1b5b3f3075
+wait_for_mode 'Ext 1'
 $TMUX set-option -g extended-keys on
 
 : >"$OUT"

screen-write.c

@@ -437,9 +437,7 @@ screen_write_reset(struct screen_write_ctx *ctx)
 
 	s->mode = MODE_CURSOR|MODE_WRAP;
 
-	if (options_get_number(global_options, "extended-keys") == 2 &&
-	    options_get_number(global_options, "extended-keys-format") !=
-	    EXTENDED_KEYS_KITTY)
+	if (options_get_number(global_options, "extended-keys") == 2)
 		s->mode = (s->mode & ~EXTENDED_KEY_MODES)|MODE_KEYS_EXTENDED;
 	input_kitty_reset(s);
 

screen.c

@@ -118,9 +118,7 @@ screen_reinit(struct screen *s, int check)
 
 	s->mode = MODE_CURSOR|MODE_WRAP|(s->mode & MODE_CRLF);
 
-	if (options_get_number(global_options, "extended-keys") == 2 &&
-	    options_get_number(global_options, "extended-keys-format") !=
-	    EXTENDED_KEYS_KITTY)
+	if (options_get_number(global_options, "extended-keys") == 2)
 		s->mode = (s->mode & ~EXTENDED_KEY_MODES)|MODE_KEYS_EXTENDED;
 	if (SCREEN_IS_ALTERNATE(s))
 		screen_alternate_off(s, NULL, 0);

tmux.1

@@ -4908,19 +4908,29 @@ If enabled, the server will exit when there are no attached clients.
 .Op Ic on | off | always
 .Xc
 Controls how modified keys are reported.
-For the
-.Ic csi\-u
-and
-.Ic xterm
-formats, this controls the
+When enabled,
+.Nm
+uses the Kitty keyboard protocol with terminals which support it, and the
 .Ic modifyOtherKeys
 .Xr xterm 1
-resource.
-For the
-.Ic kitty
-format, this controls the progressive keyboard protocol enhancements.
+resource with other terminals which support extended keys.
+Each client uses the best that its terminal supports, so clients with different
+terminals may be attached at the same time.
 .Pp
-When set to
+Programs inside panes may request either the Kitty keyboard protocol or
+.Ic modifyOtherKeys ,
+and keys are sent to each program in the form it requested, whichever client
+they were typed on.
+The Kitty keyboard protocol can report the Super and Hyper modifiers, whose key
+name prefixes are
+.Ql s-
+and
+.Ql H- ;
+its disambiguate and report-all enhancements are supported.
+.Pp
+For
+.Ic modifyOtherKeys ,
+when set to
 .Ic on ,
 the program inside the pane can request one of two modes: mode 1 which changes
 the sequence for only keys which lack an existing well-known representation; or
@@ -4929,7 +4939,8 @@ When set to
 .Ic always ,
 modes 1 and 2 can still be requested by applications, but mode 1 will be forced
 instead of the standard mode.
-This applies only to applications inside panes and does not change what
+This applies only to applications inside panes; it does not force the Kitty
+keyboard protocol or change what
 .Nm
 requests from the terminal.
 When set to
@@ -4938,19 +4949,12 @@ this feature is disabled and only standard keys are reported.
 .Pp
 .Nm
 will always request extended keys itself if the terminal supports them.
-When the
-.Ic kitty
-format is selected, it is preferred separately for each client; clients which
-do not support it use standard extended keys if available, or standard VT10x
-keys otherwise.
-Input from standard extended-key clients is translated to Kitty encoding for
-applications which have requested it.
-A Kitty keyboard state query reflects the clients attached to the window at
-the time of the query; if none are attached, the requested state is reported.
-Applications are not notified if client support changes after the reply.
+Support for the Kitty keyboard protocol is detected when a client attaches.
 See also the
+.Ic kittykeys
+and
 .Ic extkeys
-feature for the
+features for the
 .Ic terminal\-features
 option, the
 .Ic extended\-keys\-format
@@ -4962,22 +4966,9 @@ variables.
 .It Xo Ic extended\-keys\-format
 .Op Ic csi\-u | xterm | kitty
 .Xc
-Selects the format for reporting modified keys to applications.
-The
-.Ic kitty
-format uses the Kitty keyboard protocol and supports the Super and Hyper
-modifiers.
-Their key name prefixes are
-.Ql s-
-and
-.Ql H- .
-The disambiguate and report-all enhancements are supported; event types,
-alternate keys and associated text are not requested.
-For the
-.Ic csi\-u
-and
-.Ic xterm
-formats, this is the equivalent of the
+Selects the format for reporting modified keys to programs which request
+.Ic modifyOtherKeys .
+This is the equivalent of the
 .Ic formatOtherKeys
 .Xr xterm 1
 resource.
@@ -4989,10 +4980,11 @@ and as
 .Ql \[ha][[65;6u
 when set to
 .Ic csi\-u .
-With
-.Ic kitty ,
-it will be reported as
-.Ql \[ha][[97;6u .
+.Ic kitty
+is accepted for compatibility and is the same as
+.Ic csi\-u ;
+programs which request the Kitty keyboard protocol receive it whatever this
+option is set to.
 .It Xo Ic focus\-events
 .Op Ic on | off
 .Xc
@@ -5141,6 +5133,9 @@ Ignore function keys from
 and use the
 .Nm
 internal set only.
+.It kittykeys
+Supports the Kitty keyboard protocol.
+This is added automatically if the terminal answers the Kitty keyboard query.
 .It margins
 Supports DECSLRM margins.
 .It mouse

tmux.h

@@ -1829,6 +1829,7 @@ struct tty_term {
 #define TERM_VT100LIKE 0x20
 #define TERM_SIXEL 0x40
 #define TERM_INVALIDMS 0x80
+#define TERM_KITTYKEYS 0x100
 	int		 flags;
 
 	LIST_ENTRY(tty_term) entry;
@@ -1911,7 +1912,6 @@ struct tty {
 #define TTY_HAVESYNC 0x10000
 #define TTY_HAVEKKB 0x20000
 #define TTY_KKBPUSHED 0x40000
-#define TTY_KKBSUPPORT 0x80000
 #define TTY_ALL_REQUEST_FLAGS \
 	(TTY_HAVEDA|TTY_HAVEDA2|TTY_HAVEXDA|TTY_HAVESYNC|TTY_HAVEKKB)
 	int		 flags;
@@ -3545,12 +3545,10 @@ void	 input_cancel_requests(struct client *);
 
 /* input-key.c */
 void	 input_key_build(void);
-int	 input_key_pane(struct window_pane *, key_code, struct mouse_event *,
-	     int);
-int	 input_key(struct screen *, struct bufferevent *, key_code, int);
+int	 input_key_pane(struct window_pane *, key_code, struct mouse_event *);
+int	 input_key(struct screen *, struct bufferevent *, key_code);
 int	 input_key_get_mouse(struct screen *, struct mouse_event *, u_int,
 	     u_int, const char **, size_t *);
-int	 input_key_client_supports_extended(struct client *, key_code);
 
 /* input-kitty.c */
 void	 input_kitty_reset(struct screen *);

tty-features.c

@@ -235,6 +235,13 @@ static const struct tty_feature tty_feature_sync = {
 	0
 };
 
+/* Terminal supports the Kitty keyboard protocol. */
+static const struct tty_feature tty_feature_kittykeys = {
+	"kittykeys",
+	NULL,
+	TERM_KITTYKEYS
+};
+
 /* Terminal supports extended keys. */
 static const char *const tty_feature_extkeys_capabilities[] = {
 	"Eneks=\\E[>4;2m",
@@ -386,6 +393,7 @@ static const struct tty_feature *const tty_features[] = {
 	&tty_feature_extkeys,
 	&tty_feature_focus,
 	&tty_feature_ignorefkeys,
+	&tty_feature_kittykeys,
 	&tty_feature_margins,
 	&tty_feature_mouse,
 	&tty_feature_osc7,

tty-kitty.c

@@ -261,10 +261,6 @@ tty_keys_kitty_query(struct tty *tty, const char *buf, size_t len,
 	*size = 0;
 	if (tty->flags & TTY_HAVEKKB)
 		return (-1);
-	if (options_get_number(global_options, "extended-keys") == 0 ||
-	    options_get_number(global_options, "extended-keys-format") !=
-	    EXTENDED_KEYS_KITTY)
-		return (-1);
 
 	if (buf[0] != '\033')
 		return (-1);
@@ -291,8 +287,9 @@ tty_keys_kitty_query(struct tty *tty, const char *buf, size_t len,
 
 	*size = i + 1;
 	tty->kitty_keys = flags;
-	tty->flags |= (TTY_HAVEKKB|TTY_KKBSUPPORT);
+	tty->flags |= TTY_HAVEKKB;
 	log_debug("%s: received Kitty keyboard flags %u", c->name, flags);
+	tty_parse_client_features(c, "kittykeys", ",");
 	tty_update_features(tty);
 	return (0);
 }
@@ -304,18 +301,13 @@ tty_update_kitty(struct tty *tty, struct screen *s)
 	char	buf[32];
 
 	if (options_get_number(global_options, "extended-keys") == 0 ||
-	    options_get_number(global_options, "extended-keys-format") !=
-	    EXTENDED_KEYS_KITTY) {
+	    (~tty->term->flags & TERM_KITTYKEYS)) {
 		if (tty->flags & TTY_KKBPUSHED) {
 			tty_puts(tty, "\033[<u");
 			tty->flags &= ~TTY_KKBPUSHED;
 		}
 		return;
 	}
-	if ((tty->flags & (TTY_HAVEKKB|TTY_KKBSUPPORT)) !=
-	    (TTY_HAVEKKB|TTY_KKBSUPPORT))
-		return;
-
 	flags = KITTY_KEY_DISAMBIGUATE;
 	if (s != NULL && (s->kitty_keys.flags & KITTY_KEY_SUPPORTED) != 0)
 		flags = s->kitty_keys.flags & KITTY_KEY_SUPPORTED;
@@ -345,9 +337,7 @@ tty_keys_kitty(struct tty *tty, const char *buf, size_t len, size_t *size,
 	int		 result;
 
 	*size = 0;
-	if ((tty->flags & TTY_KKBPUSHED) == 0 ||
-	    options_get_number(global_options, "extended-keys-format") !=
-	    EXTENDED_KEYS_KITTY)
+	if ((tty->flags & TTY_KKBPUSHED) == 0)
 		return (-1);
 	if (len == 0 || buf[0] != '\033')
 		return (-1);

tty.c

@@ -409,10 +409,7 @@ tty_send_requests(struct tty *tty)
 		return;
 
 	if (tty->term->flags & TERM_VT100LIKE) {
-		if (~tty->flags & TTY_HAVEKKB &&
-		    options_get_number(global_options, "extended-keys") != 0 &&
-		    options_get_number(global_options, "extended-keys-format") ==
-		    EXTENDED_KEYS_KITTY)
+		if (~tty->flags & TTY_HAVEKKB)
 			tty_puts(tty, "\033[?u");
 		if (~tty->flags & TTY_HAVEDA)
 			tty_puts(tty, "\033[c");
@@ -562,19 +559,14 @@ void
 tty_update_features(struct tty *tty)
 {
 	struct client	*c = tty->client;
-	int		 extended_keys, format;
 
 	if (tty_apply_features(tty->term))
 		tty_term_apply_overrides(tty->term);
 
 	if (tty_use_margin(tty))
 		tty_putcode(tty, TTYC_ENMG);
-	extended_keys = options_get_number(global_options, "extended-keys");
-	format = options_get_number(global_options, "extended-keys-format");
-	if (extended_keys == 0 ||
-	    (format == EXTENDED_KEYS_KITTY &&
-	    (tty->flags & (TTY_HAVEKKB|TTY_KKBSUPPORT)) ==
-	    (TTY_HAVEKKB|TTY_KKBSUPPORT)))
+	if (options_get_number(global_options, "extended-keys") == 0 ||
+	    (tty->term->flags & TERM_KITTYKEYS))
 		tty_puts(tty, tty_term_string(tty->term, TTYC_DSEKS));
 	else
 		tty_puts(tty, tty_term_string(tty->term, TTYC_ENEKS));

window.c

@@ -1980,8 +1980,7 @@ window_pane_copy_paste(struct window_pane *wp, char *buf, size_t len)
 }
 
 static void
-window_pane_copy_key(struct window_pane *wp, key_code key,
-    int extended_encoding)
+window_pane_copy_key(struct window_pane *wp, key_code key)
 {
 	struct window_pane	*loop;
 
@@ -1992,7 +1991,7 @@ window_pane_copy_key(struct window_pane *wp, key_code key,
 		    (~loop->flags & PANE_INPUTOFF) &&
 		    window_pane_is_visible(loop) &&
 		    options_get_number(loop->options, "synchronize-panes"))
-			input_key_pane(loop, key, NULL, extended_encoding);
+			input_key_pane(loop, key, NULL);
 	}
 }
 
@@ -2020,7 +2019,6 @@ window_pane_key(struct window_pane *wp, struct client *c, struct session *s,
     struct winlink *wl, key_code key, struct mouse_event *m)
 {
 	struct window_mode_entry	*wme;
-	int				 extended_encoding;
 
 	if (KEYC_IS_MOUSE(key) && m == NULL)
 		return (-1);
@@ -2043,14 +2041,13 @@ window_pane_key(struct window_pane *wp, struct client *c, struct session *s,
 	if (wp->fd == -1 || wp->flags & PANE_INPUTOFF)
 		return (0);
 
-	extended_encoding = input_key_client_supports_extended(c, key);
-	if (input_key_pane(wp, key, m, extended_encoding) != 0)
+	if (input_key_pane(wp, key, m) != 0)
 		return (-1);
 
 	if (KEYC_IS_MOUSE(key))
 		return (0);
 	if (options_get_number(wp->options, "synchronize-panes"))
-		window_pane_copy_key(wp, key, extended_encoding);
+		window_pane_copy_key(wp, key);
 	return (0);
 }