diff --git a/kmod/src/format.h b/kmod/src/format.h
index 70c7d6b9..d8664927 100644
--- a/kmod/src/format.h
+++ b/kmod/src/format.h
@@ -5,11 +5,16 @@
  * The format version defines the format of structures on devices,
  * structures that are communicated over the wire, and the protocol
  * behind the structures.
+ *
+ * Builds can have unique pre-release formats that are incompatible with
+ * every other build.  This lets people experiment with formats without
+ * accidentally corrupting data with release builds.
  */
-#define SCOUTFS_FORMAT_VERSION_MIN		1
+#define SCOUTFS_FORMAT_VERSION_MIN		0x8cf3b46619eb9975ULL
 #define SCOUTFS_FORMAT_VERSION_MIN_STR	__stringify(SCOUTFS_FORMAT_VERSION_MIN)
-#define SCOUTFS_FORMAT_VERSION_MAX		1
+#define SCOUTFS_FORMAT_VERSION_MAX		0x8cf3b46619eb9975ULL
 #define SCOUTFS_FORMAT_VERSION_MAX_STR	__stringify(SCOUTFS_FORMAT_VERSION_MAX)
+#define SCOUTFS_FORMAT_VER_PREREL		0x8000000000000000ULL
 
 /* statfs(2) f_type */
 #define SCOUTFS_SUPER_MAGIC	0x554f4353		/* "SCOU" */
diff --git a/kmod/src/super.c b/kmod/src/super.c
index 0086d7fb..d7b45f13 100644
--- a/kmod/src/super.c
+++ b/kmod/src/super.c
@@ -330,7 +330,7 @@ static int scoutfs_read_super_from_bdev(struct super_block *sb,
 
 	if (le64_to_cpu(super->fmt_vers) < SCOUTFS_FORMAT_VERSION_MIN ||
 	    le64_to_cpu(super->fmt_vers) > SCOUTFS_FORMAT_VERSION_MAX) {
-		scoutfs_err(sb, "super block has format version %llu outside of supported version range %u-%u",
+		scoutfs_err(sb, "super block has format version %llu outside of supported version range %llu-%llu",
 			    le64_to_cpu(super->fmt_vers), SCOUTFS_FORMAT_VERSION_MIN,
 			    SCOUTFS_FORMAT_VERSION_MAX);
 		ret = -EINVAL;
@@ -669,6 +669,10 @@ static int __init scoutfs_module_init(void)
 	if (ret)
 		return ret;
 
+	if (SCOUTFS_FORMAT_VERSION_MIN & SCOUTFS_FORMAT_VER_PREREL) {
+		printk(KERN_INFO "scoutfs module using incompatible pre-release format version 0x%016llx.  This module can only mount volumes with this version, and volumes with this version will be incompatible with all other release builds.", SCOUTFS_FORMAT_VERSION_MIN);
+	}
+
 	scoutfs_debugfs_root = debugfs_create_dir("scoutfs", NULL);
 	if (!scoutfs_debugfs_root) {
 		ret = -ENOMEM;
diff --git a/tests/funcs/filter.sh b/tests/funcs/filter.sh
index 64f1f7c9..665aebf6 100644
--- a/tests/funcs/filter.sh
+++ b/tests/funcs/filter.sh
@@ -147,6 +147,8 @@ t_filter_dmesg()
 	# ignore systemd-journal rotating
 	re="$re|systemd-journald.*"
 
+	re="$re|incompatible pre-release format version"
+
 	egrep -v "($re)" | \
 		ignore_harmless_unwind_kasan_stack_oob
 }
diff --git a/utils/src/change_format_version.c b/utils/src/change_format_version.c
index 071e6303..6c60c89b 100644
--- a/utils/src/change_format_version.c
+++ b/utils/src/change_format_version.c
@@ -96,7 +96,7 @@ static int do_change_fmt_vers(struct change_fmt_vers_args *args)
 
 	if (le64_to_cpu(meta_super->fmt_vers) < SCOUTFS_FORMAT_VERSION_MIN ||
 	    le64_to_cpu(meta_super->fmt_vers) > SCOUTFS_FORMAT_VERSION_MAX) {
-		fprintf(stderr, "meta super block has format version %llu outside of supported version range %u-%u",
+		fprintf(stderr, "meta super block has format version %llu outside of supported version range %llu-%llu",
 			    le64_to_cpu(meta_super->fmt_vers), SCOUTFS_FORMAT_VERSION_MIN,
 			    SCOUTFS_FORMAT_VERSION_MAX);
 		ret = -EINVAL;
@@ -105,7 +105,7 @@ static int do_change_fmt_vers(struct change_fmt_vers_args *args)
 
 	if (le64_to_cpu(data_super->fmt_vers) < SCOUTFS_FORMAT_VERSION_MIN ||
 	    le64_to_cpu(data_super->fmt_vers) > SCOUTFS_FORMAT_VERSION_MAX) {
-		fprintf(stderr, "data super block has format version %llu outside of supported version range %u-%u",
+		fprintf(stderr, "data super block has format version %llu outside of supported version range %llu-%llu",
 			    le64_to_cpu(data_super->fmt_vers), SCOUTFS_FORMAT_VERSION_MIN,
 			    SCOUTFS_FORMAT_VERSION_MAX);
 		ret = -EINVAL;
@@ -186,7 +186,7 @@ static int parse_opt(int key, char *arg, struct argp_state *state)
 			return ret;
 		if (args->fmt_vers < SCOUTFS_FORMAT_VERSION_MIN ||
 		    args->fmt_vers > SCOUTFS_FORMAT_VERSION_MAX)
-			argp_error(state, "format-version %llu is outside supported range of %u-%u",
+			argp_error(state, "format-version %llu is outside supported range of %llu-%llu",
 				   args->fmt_vers, SCOUTFS_FORMAT_VERSION_MIN,
 				   SCOUTFS_FORMAT_VERSION_MAX);
 		break;
diff --git a/utils/src/cmd.c b/utils/src/cmd.c
index 10e10ca7..7ae0d36b 100644
--- a/utils/src/cmd.c
+++ b/utils/src/cmd.c
@@ -70,7 +70,7 @@ static void usage(void)
 	fprintf(stderr, "Selected fs defaults to current working directory.\n");
 	fprintf(stderr, "See <command> --help for more details.\n");
 
-	fprintf(stderr, "\nSupported format version: %u-%u\n",
+	fprintf(stderr, "\nSupported format version: %llu-%llu\n",
 			SCOUTFS_FORMAT_VERSION_MIN, SCOUTFS_FORMAT_VERSION_MAX);
 
 	fprintf(stderr, "\nCore admin:\n");
diff --git a/utils/src/mkfs.c b/utils/src/mkfs.c
index f27a5674..b9461b08 100644
--- a/utils/src/mkfs.c
+++ b/utils/src/mkfs.c
@@ -386,6 +386,10 @@ static int do_mkfs(struct mkfs_args *args)
 	print_quorum_slots(super->qconf.slots, array_size(super->qconf.slots),
 			   "                          ");
 
+	if (SCOUTFS_FORMAT_VERSION_MIN & SCOUTFS_FORMAT_VER_PREREL)
+		printf("This volume was created with the incompatible pre-release format version 0x%016llx.  This volume will only be mountable by pre-release builds with this specific matching format version.\n",
+				SCOUTFS_FORMAT_VERSION_MIN);
+
 	ret = 0;
 out:
 	if (super)
@@ -456,7 +460,7 @@ static int parse_opt(int key, char *arg, struct argp_state *state)
 			return ret;
 		if (args->fmt_vers < SCOUTFS_FORMAT_VERSION_MIN ||
 		    args->fmt_vers > SCOUTFS_FORMAT_VERSION_MAX)
-			argp_error(state, "format-version %llu is outside supported range of %u-%u",
+			argp_error(state, "format-version %llu is outside supported range of %llu-%llu",
 				   args->fmt_vers, SCOUTFS_FORMAT_VERSION_MIN,
 				   SCOUTFS_FORMAT_VERSION_MAX);
 		break;