diff --git a/input.c b/input.c
index 70caff47..3bcd7c67 100644
--- a/input.c
+++ b/input.c
@@ -1408,17 +1408,29 @@ input_csi_dispatch(struct input_ctx *ictx)
 	case INPUT_CSI_MODSET:
 		n = input_get(ictx, 0, 0, 0);
 		m = input_get(ictx, 1, 0, 0);
-		if (options_get_number(global_options, "extended-keys") == 2)
+		/*
+		 * Set the extended key reporting mode as per the client request,
+		 * unless "extended-keys always" forces us into mode 1.
+		 */
+		if (options_get_number(global_options, "extended-keys") != 1)
 			break;
-		if (n == 0 || (n == 4 && m == 0))
-			screen_write_mode_clear(sctx, MODE_KEXTENDED);
-		else if (n == 4 && (m == 1 || m == 2))
-			screen_write_mode_set(sctx, MODE_KEXTENDED);
+		screen_write_mode_clear(sctx,
+		    MODE_KEYS_EXTENDED|MODE_KEYS_EXTENDED_2);
+		if (n == 4 && m == 1)
+			screen_write_mode_set(sctx, MODE_KEYS_EXTENDED);
+		if (n == 4 && m == 2)
+			screen_write_mode_set(sctx, MODE_KEYS_EXTENDED_2);
 		break;
 	case INPUT_CSI_MODOFF:
 		n = input_get(ictx, 0, 0, 0);
-		if (n == 4)
-			screen_write_mode_clear(sctx, MODE_KEXTENDED);
+		/*
+		 * Clear the extended key reporting mode as per the client request,
+		 * unless "extended-keys always" forces us into mode 1.
+		 */
+		if (n == 4) {
+			screen_write_mode_clear(sctx,
+			    MODE_KEYS_EXTENDED|MODE_KEYS_EXTENDED_2);
+		}
 		break;
 	case INPUT_CSI_WINOPS:
 		input_csi_dispatch_winops(ictx);
diff --git a/options-table.c b/options-table.c
index 929ca5e5..738001d5 100644
--- a/options-table.c
+++ b/options-table.c
@@ -94,6 +94,9 @@ static const char *options_table_detach_on_destroy_list[] = {
 static const char *options_table_extended_keys_list[] = {
 	"off", "on", "always", NULL
 };
+static const char *options_table_extended_keys_format_list[] = {
+	"csi-u", "xterm", NULL
+};
 static const char *options_table_allow_passthrough_list[] = {
 	"off", "on", "all", NULL
 };
@@ -315,6 +318,14 @@ const struct options_table_entry options_table[] = {
 		  "that support it."
 	},
 
+	{ .name = "extended-keys-format",
+	  .type = OPTIONS_TABLE_CHOICE,
+	  .scope = OPTIONS_TABLE_SERVER,
+	  .choices = options_table_extended_keys_format_list,
+	  .default_num = 1,
+	  .text = "The format of emitted extended key sequences."
+	},
+
 	{ .name = "focus-events",
 	  .type = OPTIONS_TABLE_FLAG,
 	  .scope = OPTIONS_TABLE_SERVER,
@@ -614,7 +625,7 @@ const struct options_table_entry options_table[] = {
 	{ .name = "prefix",
 	  .type = OPTIONS_TABLE_KEY,
 	  .scope = OPTIONS_TABLE_SESSION,
-	  .default_num = '\002',
+	  .default_num = 'b'|KEYC_CTRL,
 	  .text = "The prefix key."
 	},