Client disconnect errors are now transient errors. When

  applications retry jobs that raise transient errors, jobs (e.g. web
  requests) with disconnect errors will be retried. Together with
  blocking synchronous ZEO server calls for a limited time while
  disconnected, this change should allow brief disconnections due to
  server restart to avoid generating client-visible errors (e.g. 500
  web responses).

CHANGES.rst

 Changelog
 =========
 
+- Client disconnect errors are now transient errors.  When
+  applications retry jobs that raise transient errors, jobs (e.g. web
+  requests) with disconnect errors will be retried. Together with
+  blocking synchronous ZEO server calls for a limited time while
+  disconnected, this change should allow brief disconnections due to
+  server restart to avoid generating client-visible errors (e.g. 500
+  web responses).
+
 - Fixed bugs in using the ZEO 5 client with ZEO 4 servers.
 
 5.0.0a2 (2016-07-30)

src/ZEO/Exceptions.py

@@ -13,19 +13,26 @@
 ##############################################################################
 """Exceptions for ZEO."""
 
+import transaction.interfaces
+
 from ZODB.POSException import StorageError
 
 class ClientStorageError(StorageError):
-    """An error occurred in the ZEO Client Storage."""
+    """An error occurred in the ZEO Client Storage.
+    """
 
 class UnrecognizedResult(ClientStorageError):
-    """A server call returned an unrecognized result."""
+    """A server call returned an unrecognized result.
+    """
 
-class ClientDisconnected(ClientStorageError):
-    """The database storage is disconnected from the storage."""
+class ClientDisconnected(ClientStorageError,
+                         transaction.interfaces.TransientError):
+    """The database storage is disconnected from the storage.
+    """
 
 class AuthError(StorageError):
-    """The client provided invalid authentication credentials."""
+    """The client provided invalid authentication credentials.
+    """
 
 class ProtocolError(ClientStorageError):
     """A client contacted a server with an incomparible protocol

src/ZEO/tests/testZEO.py

@@ -1411,6 +1411,14 @@ call to the server. we'd get some sort of error here.
 
 
 
+    """
+
+def ClientDisconnected_errors_are_TransientErrors():
+    """
+    >>> from ZEO.Exceptions import ClientDisconnected
+    >>> from transaction.interfaces import TransientError
+    >>> issubclass(ClientDisconnected, TransientError)
+    True
     """
 
 if sys.platform.startswith('win'):