diff --git a/bricks/_common/sources.mk b/bricks/_common/sources.mk
index 1f1215901..7ed2f6b3e 100644
--- a/bricks/_common/sources.mk
+++ b/bricks/_common/sources.mk
@@ -242,6 +242,7 @@ PBIO_SRC_C = $(addprefix lib/pbio/,\
 	sys/battery.c \
 	sys/command.c \
 	sys/core.c \
+	sys/hmi_buildhat.c \
 	sys/hmi_ev3.c \
 	sys/hmi_ev3_ui.c \
 	sys/hmi_none.c \
diff --git a/lib/pbio/platform/build_hat/pbsysconfig.h b/lib/pbio/platform/build_hat/pbsysconfig.h
index 5ccffd986..95e9a239c 100644
--- a/lib/pbio/platform/build_hat/pbsysconfig.h
+++ b/lib/pbio/platform/build_hat/pbsysconfig.h
@@ -10,7 +10,7 @@
 #define PBSYS_CONFIG_BATTERY_CHARGER                (0)
 #define PBSYS_CONFIG_HMI                            (1)
 #define PBSYS_CONFIG_HMI_STOP_BUTTON                (0) // does not exist but pbsys_main() requires this to be defined
-#define PBSYS_CONFIG_HMI_NONE                       (1)
+#define PBSYS_CONFIG_HMI_BUILDHAT                   (1)
 #define PBSYS_CONFIG_HMI_NUM_SLOTS                  (0)
 #define PBSYS_CONFIG_HOST                           (1)
 #define PBSYS_CONFIG_HOST_EVENT_OUT_SIZE            (512)
diff --git a/lib/pbio/sys/hmi_buildhat.c b/lib/pbio/sys/hmi_buildhat.c
new file mode 100644
index 000000000..c51779f45
--- /dev/null
+++ b/lib/pbio/sys/hmi_buildhat.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2018-2026 The Pybricks Authors
+
+// Provides the Human Machine Interface (HMI) for the Build HAT.
+// There is nothing to select, so the REPL starts right after boot.
+
+#include <pbsys/config.h>
+
+#if PBSYS_CONFIG_HMI_BUILDHAT
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <pbio/button.h>
+#include <pbio/light.h>
+#include <pbio/os.h>
+#include <pbsys/light.h>
+#include <pbsys/main.h>
+#include <pbsys/status.h>
+
+void pbsys_hmi_init(void) {
+}
+
+void pbsys_hmi_deinit(void) {
+}
+
+void pbsys_hmi_stop_animation(void) {
+}
+
+void pbsys_hmi_connection_changed_handler(void) {
+}
+
+pbio_error_t pbsys_hmi_await_program_selection(void) {
+
+    do {
+        if (pbsys_status_test(PBIO_PYBRICKS_STATUS_SHUTDOWN_REQUEST)) {
+            return PBIO_ERROR_CANCELED;
+        }
+        pbio_os_run_processes_and_wait_for_event();
+    } while (pbdrv_button_get_pressed());
+
+    // Start the "ready" animation, same as hmi_pup.c does after program
+    // selection.
+    #if PBSYS_CONFIG_STATUS_LIGHT_STATE_ANIMATIONS
+    pbio_color_light_start_breathe_animation(pbsys_status_light_main, PBSYS_CONFIG_STATUS_LIGHT_STATE_ANIMATIONS_HUE);
+    #elif PBSYS_CONFIG_STATUS_LIGHT
+    pbio_color_light_off(pbsys_status_light_main);
+    #endif
+
+    return pbsys_main_program_request_start(PBIO_PYBRICKS_USER_PROGRAM_ID_REPL, PBSYS_MAIN_PROGRAM_START_REQUEST_TYPE_BOOT);
+}
+
+#endif // PBSYS_CONFIG_HMI_BUILDHAT