diff --git a/include/savedata.h b/include/savedata.h
index 616c124..11f2a72 100644
--- a/include/savedata.h
+++ b/include/savedata.h
@@ -26,8 +26,7 @@ void json_load_page(struct page *page, cJSON *vars, bool call_dtors);
 union vm_value json_to_vm_value(enum ain_data_type type, enum ain_data_type struct_type, int array_rank, cJSON *json);
 
 int save_json(const char *filename, cJSON *json);
-int save_globals(const char *keyname, const char *filename);
-int save_group(const char *keyname, const char *filename, const char *group_name, int *n);
+int save_globals(const char *keyname, const char *filename, const char *group_name, int *n);
 int load_globals(const char *keyname, const char *filename, const char *group_name, int *n);
 int delete_save_file(const char *filename);
 
diff --git a/src/savedata.c b/src/savedata.c
index 45c6ffa..41cd939 100644
--- a/src/savedata.c
+++ b/src/savedata.c
@@ -14,6 +14,7 @@
  * along with this program; if not, see <http://gnu.org/licenses/>.
  */
 
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -23,6 +24,7 @@
 #include "system4.h"
 #include "system4/ain.h"
 #include "system4/file.h"
+#include "system4/savefile.h"
 #include "system4/string.h"
 
 #include "savedata.h"
@@ -77,27 +79,6 @@ cJSON *vm_value_to_json(enum ain_data_type type, union vm_value val)
 	}
 }
 
-struct global_save_data {
-	cJSON *save;
-	cJSON *globals;
-};
-
-static void init_global_save_data(struct global_save_data *data, const char *keyname)
-{
-	data->save = cJSON_CreateObject();
-	data->globals = cJSON_CreateArray();
-	cJSON_AddStringToObject(data->save, "key", keyname);
-	cJSON_AddItemToObject(data->save, "globals", data->globals);
-}
-
-static void add_global(struct global_save_data *data, int global, union vm_value val)
-{
-	cJSON *obj = cJSON_CreateObject();
-	cJSON_AddNumberToObject(obj, "index", global);
-	cJSON_AddItemToObject(obj, "value", vm_value_to_json(ain->globals[global].type.data, val));
-	cJSON_AddItemToArray(data->globals, obj);
-}
-
 int save_json(const char *filename, cJSON *json)
 {
 	char *path = savedir_path(filename);
@@ -126,25 +107,6 @@ int save_json(const char *filename, cJSON *json)
 
 }
 
-static int write_save_data(struct global_save_data *data, const char *filename)
-{
-	int r = save_json(filename, data->save);
-	cJSON_Delete(data->save);
-	return r;
-}
-
-int save_globals(const char *keyname, const char *filename)
-{
-	struct global_save_data data;
-	init_global_save_data(&data, keyname);
-
-	for (int i = 0; i < ain->nr_globals; i++) {
-		add_global(&data, i, global_get(i));
-	}
-
-	return write_save_data(&data, filename);
-}
-
 static int get_group_index(const char *name)
 {
 	for (int i = 0; i < ain->nr_global_groups; i++) {
@@ -154,27 +116,145 @@ static int get_group_index(const char *name)
 	return -1;
 }
 
-int save_group(const char *keyname, const char *filename, const char *group_name, int *n)
-{
-	int group;
+static int32_t add_value_to_gsave(enum ain_data_type type, union vm_value val, struct gsave *save);
 
-	if ((group = get_group_index(group_name)) < 0) {
-		WARNING("Unregistered global group: %s", display_sjis0(group_name));
+static struct gsave_flat_array *collect_flat_arrays(struct page *page, struct gsave_flat_array *fa, struct gsave *save)
+{
+	if (page->array.rank > 1) {
+		for (int i = 0; i < page->nr_vars; i++)
+			fa = collect_flat_arrays(heap_get_page(page->values[i].i), fa, save);
+		return fa;
+	}
+	fa->nr_values = page->nr_vars;
+	fa->values = xcalloc(fa->nr_values, sizeof(struct gsave_array_value));
+	for (int i = 0; i < page->nr_vars; i++) {
+		enum ain_data_type type = variable_type(page, i, NULL, NULL);
+		fa->values[i].type = type;
+		fa->values[i].value = add_value_to_gsave(type, page->values[i], save);
+	}
+	return ++fa;
+}
+
+static int32_t add_value_to_gsave(enum ain_data_type type, union vm_value val, struct gsave *save)
+{
+	switch (type) {
+	case AIN_VOID:
+	case AIN_INT:
+	case AIN_BOOL:
+	case AIN_FUNC_TYPE:
+	case AIN_DELEGATE:
+	case AIN_LONG_INT:
+	case AIN_FLOAT:
+		return val.i;
+	case AIN_STRING:
+		return gsave_add_string(save, heap[val.i].s);
+	case AIN_STRUCT:
+		{
+			struct page *page = heap_get_page(val.i);
+			assert(page->type == STRUCT_PAGE);
+			struct ain_struct *st = &ain->structures[page->index];
+			assert(st->nr_members == page->nr_vars);
+			struct gsave_record rec = {
+				.type = GSAVE_RECORD_STRUCT,
+				.struct_name = strdup(st->name),
+				.nr_indices = st->nr_members,
+				.indices = xcalloc(st->nr_members, sizeof(int32_t)),
+			};
+			for (int i = 0; i < page->nr_vars; i++) {
+				enum ain_data_type type = st->members[i].type.data;
+				int32_t value = add_value_to_gsave(type, page->values[i], save);
+				struct gsave_keyval kv = {
+					.name = strdup(st->members[i].name),
+					.type = type,
+					.value = value,
+				};
+				rec.indices[i] = gsave_add_keyval(save, &kv);
+			}
+			return gsave_add_record(save, &rec);
+		}
+	case AIN_ARRAY_TYPE:
+		{
+			struct page *page = heap_get_page(val.i);
+			if (!page) {
+				struct gsave_array array = { .rank = -1 };
+				return gsave_add_array(save, &array);
+			}
+			assert(page->type == ARRAY_PAGE);
+			struct gsave_array array = {
+				.rank = page->array.rank,
+				.dimensions = xcalloc(page->array.rank, sizeof(int32_t)),
+				.nr_flat_arrays = 1
+			};
+			for (struct page *p = page;; p = heap_get_page(page->values[0].i)) {
+				array.dimensions[p->array.rank - 1] = p->nr_vars;
+				if (p->array.rank == 1)
+					break;
+				array.nr_flat_arrays *= p->nr_vars;
+			}
+			array.flat_arrays = xcalloc(array.nr_flat_arrays, sizeof(struct gsave_flat_array));
+			collect_flat_arrays(page, array.flat_arrays, save);
+			return gsave_add_array(save, &array);
+		}
+	case AIN_REF_TYPE:
+		return -1;
+	default:
+		WARNING("Unhandled type: %s", ain_strtype(ain, type, -1));
+		return -1;
+	}
+}
+
+int save_globals(const char *keyname, const char *filename, const char *group_name, int *n_out)
+{
+	int group = -1;
+	int nr_vars;
+	if (group_name) {
+		if ((group = get_group_index(group_name)) < 0) {
+			WARNING("Unregistered global group: %s", display_sjis0(group_name));
+			return 0;
+		}
+		nr_vars = 0;
+		for (int i = 0; i < ain->nr_globals; i++) {
+			if (ain->globals[i].group_index == group)
+				nr_vars++;
+		}
+	} else {
+		nr_vars = ain->nr_globals;
+	}
+
+	int gsave_version = AIN_VERSION_GTE(ain, 5, 0) ? 5 : 4;
+	struct gsave *save = gsave_create(gsave_version, keyname, ain->nr_globals, group_name);
+	gsave_add_globals_record(save, nr_vars);
+
+	struct gsave_global *global = save->globals;
+	for (int i = 0; i < ain->nr_globals; i++) {
+		if (group >= 0 && ain->globals[i].group_index != group)
+			continue;
+		global->name = strdup(ain->globals[i].name);
+		global->type = ain->globals[i].type.data;
+		global->value = add_value_to_gsave(global->type, global_get(i), save);
+		global++;
+	}
+
+	char *path = savedir_path(filename);
+	FILE *fp = file_open_utf8(path, "wb");
+	if (!fp) {
+		WARNING("Failed to open save file %s: %s", display_utf0(path), strerror(errno));
+		free(path);
+		gsave_free(save);
 		return 0;
 	}
+	free(path);
 
-	struct global_save_data data;
-	init_global_save_data(&data, keyname);
-
-	*n = 0;
-	for (int i = 0; i < ain->nr_globals; i++) {
-		if (ain->globals[i].group_index != group)
-			continue;
-		add_global(&data, i, global_get(i));
-		(*n)++;
-	}
-
-	return write_save_data(&data, filename);
+	bool encrypt = !AIN_VERSION_GTE(ain, 6, 0);
+	int compression_level = AIN_VERSION_GTE(ain, 6, 0) ? 1 : 9;
+	enum savefile_error error = gsave_write(save, fp, encrypt, compression_level);
+	if (error != SAVEFILE_SUCCESS)
+		WARNING("Failed to write save file: %s", savefile_strerror(error));
+	fclose(fp);
+	gsave_free(save);
+	if (n_out)
+		*n_out = nr_vars;
+	return error == SAVEFILE_SUCCESS;
 }
 
 union vm_value json_to_vm_value(enum ain_data_type type, enum ain_data_type struct_type, int array_rank, cJSON *json);
@@ -273,19 +353,16 @@ union vm_value json_to_vm_value(enum ain_data_type type, enum ain_data_type stru
 	}
 }
 
-static cJSON *read_save_file(const char *filename)
+static cJSON *read_save_file(const char *path)
 {
 	FILE *f;
 	long len;
 	char *buf;
-	char *path = savedir_path(filename);
 
 	if (!(f = file_open_utf8(path, "rb"))) {
-		WARNING("Failed to open save file: %s: %s", display_utf0(filename), strerror(errno));
-		free(path);
+		WARNING("Failed to open save file: %s: %s", display_utf0(path), strerror(errno));
 		return NULL;
 	}
-	free(path);
 
 	fseek(f, 0, SEEK_END);
 	len = ftell(f);
@@ -294,7 +371,7 @@ static cJSON *read_save_file(const char *filename)
 	buf = xmalloc(len+1);
 	buf[len] = '\0';
 	if (fread(buf, len, 1, f) != 1) {
-		WARNING("Failed to read save file: %s", display_utf0(filename));
+		WARNING("Failed to read save file: %s", display_utf0(path));
 		free(buf);
 		return 0;
 	}
@@ -305,10 +382,10 @@ static cJSON *read_save_file(const char *filename)
 	return r;
 }
 
-int load_globals(const char *keyname, const char *filename, const char *group_name, int *n)
+static int load_globals_from_json(const char *path, const char *keyname, const char *group_name, int *n)
 {
 	int retval = 0;
-	cJSON *save = read_save_file(filename);
+	cJSON *save = read_save_file(path);
 	if (!save)
 		return 0;
 	if (!cJSON_IsObject(save)) {
@@ -365,6 +442,160 @@ cleanup:
 	return retval;
 }
 
+static int struct_member_index(struct ain_struct *st, const char *name)
+{
+	for (int i = 0; i < st->nr_members; i++) {
+		if (!strcmp(st->members[i].name, name))
+			return i;
+	}
+	return -1;
+}
+
+static union vm_value gsave_to_vm_value(struct gsave *save, enum ain_data_type type, int struct_type, int array_rank, int32_t value);
+
+static struct gsave_flat_array *gsave_load_array(struct gsave *save, struct page *page, struct gsave_flat_array *flat_array)
+{
+	assert(page->type == ARRAY_PAGE);
+	if (page->array.rank > 1) {
+		for (int i = 0; i < page->nr_vars; i++)
+			flat_array = gsave_load_array(save, heap_get_page(page->values[i].i), flat_array);
+		return flat_array;
+	}
+
+	if (page->nr_vars != flat_array->nr_values)
+		VM_ERROR("Bad save file: unexpected number of array elements");
+	for (int i = 0; i < page->nr_vars; i++) {
+		int struct_type, array_rank;
+		enum ain_data_type data_type = variable_type(page, i, &struct_type, &array_rank);
+		if (data_type != flat_array->values[i].type)
+			VM_ERROR("Bad save file: unexpected array element type");
+		union vm_value val = gsave_to_vm_value(save, data_type, struct_type, array_rank, flat_array->values[i].value);
+		page->values[i] = val;
+	}
+	return flat_array + 1;
+}
+
+static union vm_value gsave_to_vm_value(struct gsave *save, enum ain_data_type type, int struct_type, int array_rank, int32_t value)
+{
+	switch (type) {
+	case AIN_VOID:
+	case AIN_INT:
+	case AIN_BOOL:
+	case AIN_LONG_INT:
+	case AIN_FLOAT:
+		return vm_int(value);
+	case AIN_STRING:
+		{
+			int slot = heap_alloc_slot(VM_STRING);
+			heap[slot].s = string_ref(save->strings[value]);
+			return vm_int(slot);
+		}
+	case AIN_STRUCT:
+		{
+			struct gsave_record *rec = &save->records[value];
+			struct ain_struct *st = &ain->structures[struct_type];
+			if (strcmp(rec->struct_name, st->name))
+				VM_ERROR("Bad save file: structure name mismatch");
+			int slot = alloc_struct(struct_type);
+			struct page *page = heap[slot].page;
+			for (int i = 0; i < rec->nr_indices; i++) {
+				struct gsave_keyval *kv = &save->keyvals[rec->indices[i]];
+				int index = struct_member_index(st, kv->name);
+				if (index < 0)
+					VM_ERROR("Bad save file: %s has no member named %s", display_sjis0(rec->struct_name), display_sjis1(kv->name));
+				int struct_type, array_rank;
+				enum ain_data_type data_type = variable_type(page, index, &struct_type, &array_rank);
+				if (data_type != kv->type)
+					VM_ERROR("Bad save file: structure member type mismatch");
+				union vm_value val = gsave_to_vm_value(save, data_type, struct_type, array_rank, kv->value);
+				page->values[index] = val;
+			}
+			return vm_int(slot);
+		}
+	case AIN_ARRAY_TYPE:
+		{
+			struct gsave_array *array = &save->arrays[value];
+			int slot = heap_alloc_slot(VM_PAGE);
+			if (array->rank == -1) {
+				heap[slot].page = NULL;
+				return vm_int(slot);
+			}
+			if (array_rank != array->rank)
+				VM_ERROR("Bad save file: array rank mismatch");
+			union vm_value *dims = xmalloc(sizeof(union vm_value) * array_rank);
+			for (int i = 0; i < array_rank; i++)
+				dims[i].i = array->dimensions[array_rank - 1 - i];
+			struct page *page = alloc_array(array_rank, dims, type, struct_type, false);
+			heap[slot].page = page;
+			free(dims);
+			gsave_load_array(save, page, array->flat_arrays);
+			return vm_int(slot);
+		}
+	case AIN_REF_TYPE:
+		return vm_int(-1);
+	default:
+		WARNING("Unhandled data type: %s", ain_strtype(ain, type, -1));
+		return vm_int(-1);
+	}
+}
+
+int load_globals_from_gsave(struct gsave *save, const char *keyname, const char *group_name, int *n)
+{
+	if (strcmp(keyname, save->key))
+		VM_ERROR("Attempted to load save data with wrong key: %s", display_sjis0(keyname));
+	if (!group_name)
+		group_name = "";
+	if (!save->group)
+		save->group = strdup("");
+	if (strcmp(group_name, save->group))
+		VM_ERROR("Attempted to load save data with wrong group name: '%s'", display_sjis0(group_name));
+
+	for (struct gsave_global *g = save->globals; g < save->globals + save->nr_globals; g++) {
+		int global_index = ain_get_global(ain, g->name);
+		if (global_index < 0) {
+			WARNING("invalid global name %s", display_sjis0(g->name));
+			return 0;
+		}
+		struct ain_type *type = &ain->globals[global_index].type;
+		if (type->data != g->type) {
+			WARNING("%s: type mismatch", display_sjis0(g->name));
+			return 0;
+		}
+		bool call_dtors = false; // Destructors for old objects should not be called.
+		global_set(global_index, gsave_to_vm_value(save, type->data, type->struc, type->rank, g->value), call_dtors);
+		if (n)
+			(*n)++;
+	}
+
+	return 1;
+}
+
+int load_globals(const char *keyname, const char *filename, const char *group_name, int *n)
+{
+	char *path = savedir_path(filename);
+	int retval;
+
+	// First, try reading as a gsave.
+	enum savefile_error error;
+	struct gsave *save = gsave_read(path, &error);
+	switch (error) {
+	case SAVEFILE_SUCCESS:
+		free(path);
+		retval = load_globals_from_gsave(save, keyname, group_name, n);
+		gsave_free(save);
+		return retval;
+	case SAVEFILE_INVALID_SIGNATURE:
+		// If not a System4 save file, try reading as a json.
+		retval = load_globals_from_json(path, keyname, group_name, n);
+		free(path);
+		return retval;
+	default:
+		WARNING("%s: %s", display_utf0(path), savefile_strerror(error));
+		free(path);
+		return 0;
+	}
+}
+
 int delete_save_file(const char *filename)
 {
 	char *path = savedir_path(filename);
diff --git a/src/vm.c b/src/vm.c
index 042a6e0..547ff8c 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -429,7 +429,7 @@ static void system_call(enum syscall_code code)
 	case SYS_GLOBAL_SAVE: { // system.GlobalSave(string szKeyName, string szFileName)
 		int filename = stack_pop().i;
 		int keyname = stack_pop().i;
-		stack_push(save_globals(heap_get_string(keyname)->text, heap_get_string(filename)->text));
+		stack_push(save_globals(heap_get_string(keyname)->text, heap_get_string(filename)->text, NULL, NULL));
 		heap_unref(filename);
 		heap_unref(keyname);
 		break;
@@ -603,7 +603,7 @@ static void system_call(enum syscall_code code)
 		int groupname = stack_pop().i;
 		int filename = stack_pop().i;
 		int keyname = stack_pop().i;
-		stack_push(save_group(heap_get_string(keyname)->text,
+		stack_push(save_globals(heap_get_string(keyname)->text,
 				      heap_get_string(filename)->text,
 				      heap_get_string(groupname)->text,
 				      &n->i));
diff --git a/subprojects/libsys4 b/subprojects/libsys4
index 187a463..b869f6c 160000
--- a/subprojects/libsys4
+++ b/subprojects/libsys4
@@ -1 +1 @@
-Subproject commit 187a463044a0b9b207f322796aa20c42322fed98
+Subproject commit b869f6cc8d6f417272de6a2f01ef66473cb06e22