diff --git a/lib/libsys/open.2.xattr b/lib/libsys/open.2
--- a/lib/libsys/open.2.xattr
+++ b/lib/libsys/open.2
@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd February 28, 2025
+.Dd April 3, 2025
 .Dt OPEN 2
 .Os
 .Sh NAME
@@ -210,6 +210,8 @@
 open file referenced by
 .Fa fd
 if path is empty
+.It Dv O_NAMEDATTR
+open a named attribute or named attribute directory
 .El
 .Pp
 Exactly one of the flags
@@ -499,6 +501,44 @@
 .Dv O_CLOEXEC
 flag.
 .Pp
+The
+.Dv O_NAMEDATTR
+flag specifies that a named attribute or named attribute directory be
+opened.
+For
+.Fn open
+or
+.Fn openat
+where the
+.Fa fd
+represents an open file in the file system's directory namespace,
+this option flag indicates that the named attribute directory should
+be opened.
+If the
+.Dv O_CREAT
+flag has been specified as well, the named attribute directory will be
+created if it does not exist.
+If the
+.Dv O_CREAT
+flag has not been specified and there is no named attribute directory
+for the file object, an
+.Fn open
+or
+.Fn openat
+will return
+.Er ENOATTR .
+If the
+.Fn openat
+argument
+.Fa fd
+is an open named attribute directory, the
+.Fa path
+argument must be a single component name and is the name of a named
+attribute for the file object.
+(See
+.Xr named_attribute 9
+for more information.)
+.Pp
 The system imposes a limit on the number of file descriptors
 open simultaneously by one process.
 The
@@ -730,6 +770,10 @@
 .Dv vfs.lookup_cap_dotdot
 .Xr sysctl 3
 is set, and the process is in capability mode.
+.It Bq Er ENOATTR
+.Dv O_NAMEDATTR
+has been specified, but there is no named attribute or named attribute
+directory.
 .El
 .Sh SEE ALSO
 .Xr chmod 2 ,
@@ -745,7 +789,8 @@
 .Xr umask 2 ,
 .Xr write 2 ,
 .Xr fopen 3 ,
-.Xr capsicum 4
+.Xr capsicum 4 ,
+.Xr named_attribute 9
 .Sh STANDARDS
 These functions are specified by
 .St -p1003.1-2008 .
@@ -794,6 +839,8 @@
 .Fx 8.0 .
 .Dv O_DSYNC
 appeared in 13.0.
+.Dv O_NAMEDATTR
+appeared in 15.0.
 .Sh BUGS
 The
 .Fa mode