diff --git a/kmod/src/attr_x.c b/kmod/src/attr_x.c
index 56718197..39e84a36 100644
--- a/kmod/src/attr_x.c
+++ b/kmod/src/attr_x.c
@@ -33,6 +33,10 @@ static int validate_attr_x_input(struct super_block *sb, struct scoutfs_ioctl_in
 	    (ret = scoutfs_fmt_vers_unsupported(sb, SCOUTFS_FORMAT_VERSION_FEAT_RETENTION)))
 		    return ret;
 
+	if ((iax->x_mask & SCOUTFS_IOC_IAX_PROJECT_ID) &&
+	    (ret = scoutfs_fmt_vers_unsupported(sb, SCOUTFS_FORMAT_VERSION_FEAT_PROJECT_ID)))
+		    return ret;
+
 	return 0;
 }
 
@@ -111,6 +115,8 @@ int scoutfs_get_attr_x(struct inode *inode, struct scoutfs_ioctl_inode_attr_x *i
 			bits |= SCOUTFS_IOC_IAX_B_RETENTION;
 		size = fill_attr(size, iax, SCOUTFS_IOC_IAX__BITS, bits, bits);
 	}
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_PROJECT_ID,
+			 project_id, scoutfs_inode_get_proj(inode));
 
 	ret = size;
 unlock:
@@ -230,6 +236,8 @@ int scoutfs_set_attr_x(struct inode *inode, struct scoutfs_ioctl_inode_attr_x *i
 					(iax->bits & SCOUTFS_IOC_IAX_B_RETENTION) ?
 					SCOUTFS_INO_FLAG_RETENTION : 0);
 	}
+	if (iax->x_mask & SCOUTFS_IOC_IAX_PROJECT_ID)
+		scoutfs_inode_set_proj(inode, iax->project_id);
 
 	scoutfs_update_inode_item(inode, lock, &ind_locks);
 	ret = 0;
diff --git a/kmod/src/dir.c b/kmod/src/dir.c
index e382c78d..c8417bdf 100644
--- a/kmod/src/dir.c
+++ b/kmod/src/dir.c
@@ -672,6 +672,8 @@ retry:
 	if (ret < 0)
 		goto out;
 
+	scoutfs_inode_set_proj(inode, scoutfs_inode_get_proj(dir));
+
 	ret = scoutfs_dirty_inode_item(dir, *dir_lock);
 out:
 	if (ret)
diff --git a/kmod/src/format.h b/kmod/src/format.h
index 88abb822..7e283de8 100644
--- a/kmod/src/format.h
+++ b/kmod/src/format.h
@@ -12,6 +12,7 @@
 #define SCOUTFS_FORMAT_VERSION_MAX_STR	__stringify(SCOUTFS_FORMAT_VERSION_MAX)
 
 #define SCOUTFS_FORMAT_VERSION_FEAT_RETENTION	2
+#define SCOUTFS_FORMAT_VERSION_FEAT_PROJECT_ID	2
 
 /* statfs(2) f_type */
 #define SCOUTFS_SUPER_MAGIC	0x554f4353		/* "SCOU" */
@@ -861,8 +862,11 @@ struct scoutfs_inode {
 	struct scoutfs_timespec ctime;
 	struct scoutfs_timespec mtime;
 	struct scoutfs_timespec crtime;
+	__le64 proj;
 };
 
+#define SCOUTFS_INODE_FMT_V1_BYTES offsetof(struct scoutfs_inode, proj)
+
 /*
  * There are so few versions that we don't mind doing this work inline
  * so that both utils and kernel can share these.  Mounting has already
@@ -872,7 +876,10 @@ struct scoutfs_inode {
 /* Returns the native written inode size for the given format version, 0 for bad version */
 static inline int scoutfs_inode_vers_bytes(__u64 fmt_vers)
 {
-	return sizeof(struct scoutfs_inode);
+	if (fmt_vers == 1)
+		return SCOUTFS_INODE_FMT_V1_BYTES;
+	else
+		return sizeof(struct scoutfs_inode);
 }
 /*
  * Returns true if bytes is a valid inode size to read from the given
@@ -881,7 +888,8 @@ static inline int scoutfs_inode_vers_bytes(__u64 fmt_vers)
  */
 static inline int scoutfs_inode_valid_vers_bytes(__u64 fmt_vers, int bytes)
 {
-	return bytes == sizeof(struct scoutfs_inode);
+	return (bytes == sizeof(struct scoutfs_inode) && fmt_vers == SCOUTFS_FORMAT_VERSION_MAX) ||
+	       (bytes == SCOUTFS_INODE_FMT_V1_BYTES);
 }
 
 #define SCOUTFS_INO_FLAG_TRUNCATE	0x1
diff --git a/kmod/src/inode.c b/kmod/src/inode.c
index 4bd1492b..2203a8e9 100644
--- a/kmod/src/inode.c
+++ b/kmod/src/inode.c
@@ -278,6 +278,7 @@ static void load_inode(struct inode *inode, struct scoutfs_inode *cinode, int in
 	si->flags = le32_to_cpu(cinode->flags);
 	si->crtime.tv_sec = le64_to_cpu(cinode->crtime.sec);
 	si->crtime.tv_nsec = le32_to_cpu(cinode->crtime.nsec);
+	si->proj = le64_to_cpu(cinode->proj);
 
 	/*
 	 * i_blocks is initialized from online and offline and is then
@@ -734,6 +735,29 @@ void scoutfs_inode_set_flags(struct inode *inode, u32 and, u32 or)
 	write_sequnlock(&si->seqlock);
 }
 
+u64 scoutfs_inode_get_proj(struct inode *inode)
+{
+	struct scoutfs_inode_info *si = SCOUTFS_I(inode);
+	unsigned seq;
+	u64 proj;
+
+	do {
+		seq = read_seqbegin(&si->seqlock);
+		proj = si->proj;
+	} while (read_seqretry(&si->seqlock, seq));
+
+	return proj;
+}
+
+void scoutfs_inode_set_proj(struct inode *inode, u64 proj)
+{
+	struct scoutfs_inode_info *si = SCOUTFS_I(inode);
+
+	write_seqlock(&si->seqlock);
+	si->proj = proj;
+	write_sequnlock(&si->seqlock);
+}
+
 static int scoutfs_iget_test(struct inode *inode, void *arg)
 {
 	struct scoutfs_inode_info *si = SCOUTFS_I(inode);
@@ -879,6 +903,7 @@ static void store_inode(struct scoutfs_inode *cinode, struct inode *inode, int i
 	cinode->crtime.sec = cpu_to_le64(si->crtime.tv_sec);
 	cinode->crtime.nsec = cpu_to_le32(si->crtime.tv_nsec);
 	memset(cinode->crtime.__pad, 0, sizeof(cinode->crtime.__pad));
+	cinode->proj = cpu_to_le64(si->proj);
 }
 
 /*
@@ -1527,6 +1552,7 @@ int scoutfs_new_inode(struct super_block *sb, struct inode *dir, umode_t mode, d
 	si->offline_blocks = 0;
 	si->next_readdir_pos = SCOUTFS_DIRENT_FIRST_POS;
 	si->next_xattr_id = 0;
+	si->proj = 0;
 	si->have_item = false;
 	atomic64_set(&si->last_refreshed, lock->refresh_gen);
 	scoutfs_lock_add_coverage(sb, lock, &si->ino_lock_cov);
diff --git a/kmod/src/inode.h b/kmod/src/inode.h
index 6ab7d220..e068cee5 100644
--- a/kmod/src/inode.h
+++ b/kmod/src/inode.h
@@ -21,6 +21,7 @@ struct scoutfs_inode_info {
 	u64 data_version;
 	u64 online_blocks;
 	u64 offline_blocks;
+	u64 proj;
 	u32 flags;
 	struct kc_timespec crtime;
 
@@ -122,6 +123,9 @@ u64 scoutfs_inode_data_version(struct inode *inode);
 void scoutfs_inode_get_onoff(struct inode *inode, s64 *on, s64 *off);
 u32 scoutfs_inode_get_flags(struct inode *inode);
 void scoutfs_inode_set_flags(struct inode *inode, u32 and, u32 or);
+u64 scoutfs_inode_get_proj(struct inode *inode);
+void scoutfs_inode_set_proj(struct inode *inode, u64 proj);
+
 int scoutfs_complete_truncate(struct inode *inode, struct scoutfs_lock *lock);
 
 int scoutfs_inode_check_retention(struct inode *inode);
diff --git a/kmod/src/ioctl.h b/kmod/src/ioctl.h
index fbb04217..9a6b9b30 100644
--- a/kmod/src/ioctl.h
+++ b/kmod/src/ioctl.h
@@ -687,6 +687,7 @@ struct scoutfs_ioctl_inode_attr_x {
 	__u64 crtime_sec;
 	__u64 size;
 	__u64 bits;
+	__u64 project_id;
 };
 
 /*
@@ -736,11 +737,12 @@ struct scoutfs_ioctl_inode_attr_x {
 #define SCOUTFS_IOC_IAX_CRTIME		(1ULL << 6)
 #define SCOUTFS_IOC_IAX_SIZE		(1ULL << 7)
 #define SCOUTFS_IOC_IAX_RETENTION	(1ULL << 8)
+#define SCOUTFS_IOC_IAX_PROJECT_ID	(1ULL << 9)
 
 /* single bit attributes that are packed in the bits field as _B_ */
 #define SCOUTFS_IOC_IAX__BITS		(SCOUTFS_IOC_IAX_RETENTION)
 /* inverse of all the bits we understand */
-#define SCOUTFS_IOC_IAX__UNKNOWN	(U64_MAX << 9)
+#define SCOUTFS_IOC_IAX__UNKNOWN	(U64_MAX << 10)
 
 #define SCOUTFS_IOC_GET_ATTR_X \
 	_IOW(SCOUTFS_IOCTL_MAGIC, 18, struct scoutfs_ioctl_inode_attr_x)
diff --git a/utils/man/scoutfs.5 b/utils/man/scoutfs.5
index 839c8cd9..458d69a3 100644
--- a/utils/man/scoutfs.5
+++ b/utils/man/scoutfs.5
@@ -312,6 +312,19 @@ with sufficient priveledges to remove the retention restrictions on
 other modifications.
 .RE
 
+.SH PROJECT IDs
+All inodes have a project ID attribute that can be set via the
+SET_ATTR_X ioctl and displayed with the GET_ATTR_X ioctl.  Project IDs
+are an unsigned 64bit value and the value of 0 is reserved to indicate
+that no project ID is assigned.   If a project ID is set on a directory
+then all inodes created with it as the initial parent inheret that ID,
+for all file types.  This includes files initially unlinked from the
+namespace when created with O_TMPFILE.  Project IDs are only
+automatically inherited from the parent dir on initial creation.
+They're not changed as directory entry linkes to the inode are created
+or renamed.
+.RE
+
 .SH FORMAT VERSION
 The format version defines the layout and use of structures stored on
 devices and passed over the network.  The version is incremented for
@@ -399,7 +412,8 @@ The defined format versions are:
 Initial format version.
 .TP
 .B 2
-Added retention mode by setting the retention attribute.
+Added retention mode by setting the retention attribute.  Added the
+project ID inode attribute.
 .RE
 
 .SH CORRUPTION DETECTION
diff --git a/utils/src/attr_x.c b/utils/src/attr_x.c
index 979ac517..9674624e 100644
--- a/utils/src/attr_x.c
+++ b/utils/src/attr_x.c
@@ -82,6 +82,7 @@ static int do_attr_x(struct attr_x_args *args)
 		pr(iax, CRTIME, "crtime", "%llu.%u", iax->crtime_sec, iax->crtime_nsec);
 		pr(iax, SIZE, "size", "%llu", iax->size);
 		prb(iax, RETENTION, "retention");
+		pr(iax, PROJECT_ID, "project_id", "%llu", iax->project_id);
 	}
 
 	ret = 0;
@@ -191,6 +192,14 @@ static int parse_opt(int key, char *arg, struct argp_state *state)
 				args->iax.bits |= SCOUTFS_IOC_IAX_B_RETENTION;
 		}
 		break;
+	case 'p':
+		args->iax.x_mask |= SCOUTFS_IOC_IAX_PROJECT_ID;
+		if (arg) {
+			ret = parse_u64(arg, &args->iax.project_id);
+			if (ret)
+				return ret;
+		}
+		break;
 	case ARGP_KEY_ARG:
 		if (!args->filename)
 			args->filename = strdup_or_error(state, arg);
@@ -222,6 +231,7 @@ static struct argp_option set_options[] = {
 	{ "crtime", 'r', "SECS.NSECS", 0, "ScoutFS creation time"},
 	{ "size", 's', "SIZE", 0, "Inode i_size field"},
 	{ "retention", 't', "0|1", 0, "Retention flag"},
+	{ "project_id", 'p', "PROJECT_ID", 0, "Project ID"},
 	{ NULL }
 };
 
diff --git a/utils/src/print.c b/utils/src/print.c
index b977da46..e3f81780 100644
--- a/utils/src/print.c
+++ b/utils/src/print.c
@@ -49,7 +49,7 @@ static void print_inode(struct scoutfs_key *key, void *val, int val_len)
 {
 	struct scoutfs_inode *inode = val;
 
-	printf("    inode: ino %llu size %llu version %llu nlink %u\n"
+	printf("    inode: ino %llu size %llu version %llu proj %llu nlink %u\n"
 	       "      uid %u gid %u mode 0%o rdev 0x%x flags 0x%x\n"
 	       "      next_readdir_pos %llu meta_seq %llu data_seq %llu data_version %llu\n"
 	       "      atime %llu.%08u ctime %llu.%08u\n"
@@ -57,6 +57,7 @@ static void print_inode(struct scoutfs_key *key, void *val, int val_len)
 	       le64_to_cpu(key->ski_ino),
 	       le64_to_cpu(inode->size),
 	       le64_to_cpu(inode->version),
+	       le64_to_cpu(inode->proj),
 	       le32_to_cpu(inode->nlink), le32_to_cpu(inode->uid),
 	       le32_to_cpu(inode->gid), le32_to_cpu(inode->mode),
 	       le32_to_cpu(inode->rdev),