Found out how to do it in lvgl 8:
if (lv_event_get_code(e) == LV_EVENT_VALUE_CHANGED) {
lv_obj_t* tabview = lv_event_get_target(e);
lv_obj_t* tabContainer = lv_tabview_get_content(tabview);
lv_anim_t* anim = lv_anim_get(tabContainer, NULL);
if(anim) {
lv_anim_set_ready_cb(anim, ready_cb);
}
}