@@ -21,7 +21,7 @@ flag (or its long form ``--help``)::
               [--warn-unused-ignores] [--warn-unused-configs]
               [--show-error-context] [--no-implicit-optional] [--no-incremental]
               [--quick-and-dirty] [--cache-dir DIR] [--cache-fine-grained]
-              [--skip-version-check] [--strict-optional]
+              [--skip-version-check] [--no-strict-optional]
               [--strict-optional-whitelist [GLOB [GLOB ...]]]
               [--always-true NAME] [--always-false NAME] [--junit-xml JUNIT_XML]
               [--pdb] [--show-traceback] [--stats] [--inferstats]
@@ -298,11 +298,14 @@ Here are some more useful flags:
 - ``--ignore-missing-imports`` suppresses error messages about imports
   that cannot be resolved (see :ref:`follow-imports` for some examples).
 
-- ``--strict-optional`` enables strict checking of ``Optional[...]``
-  types and ``None`` values. Without this option, mypy doesn't
+- ``--no-strict-optional`` disables strict checking of ``Optional[...]``
+  types and ``None`` values. With this option, mypy doesn't
   generally check the use of ``None`` values -- they are valid
-  everywhere. See :ref:`strict_optional` for more about this feature.
-  This flag will become the default in the near future.
+  everywhere. See :ref:`no_strict_optional` for more about this feature.
+
+  **Note:** Strict optional checking was enabled by default starting in
+  mypy 0.600, and in previous versions it had to be explicitly enabled
+  using ``--strict-optional`` (which is still accepted).
 
 - ``--disallow-untyped-defs`` reports an error whenever it encounters
   a function definition without type annotations.
 
@@ -51,7 +51,7 @@ flagged as an error.
 
   If you don't know what types to add, you can use ``Any``, but beware:
 
-- **One of the values involved has type ``Any``.** Extending the above
+- **One of the values involved has type 'Any'.** Extending the above
   example, if we were to leave out the annotation for ``a``, we'd get
   no error:
 
@@ -85,17 +85,16 @@ flagged as an error.
   clarity about the latter use ``--follow-imports=error``.  You can
   read up about these and other useful flags in :ref:`command-line`.
 
-- **A function annotated as returning a non-optional type returns ``None``
+- **A function annotated as returning a non-optional type returns 'None'
   and mypy doesn't complain**.
 
   .. code-block:: python
 
       def foo() -> str:
           return None  # No error!
 
-  By default, the ``None`` value is considered compatible with everything. See
-  :ref:`optional` for details on strict optional checking, which allows mypy to
-  check ``None`` values precisely, and will soon become default.
+  You may have disabled strict optional checking (see
+  :ref:`no_strict_optional` for more).
 
 .. _silencing_checker:
 
@@ -131,6 +130,17 @@ The second line is now fine, since the ignore comment causes the name
     if we did have a stub available for ``frobnicate`` then mypy would
     ignore the ``# type: ignore`` comment and typecheck the stub as usual.
 
+
+Unexpected errors about 'None' and/or 'Optional' types
+------------------------------------------------------
+
+Starting from mypy 0.600, mypy uses
+:ref:`strict optional checking <strict_optional>` by default,
+and ``None`` is not compatible with non-optional types.  It's
+easy to switch back to the older behavior where ``None`` was
+compatible with arbitrary types (see :ref:`no_strict_optional`).
+
+
 Types of empty collections
 --------------------------
 
 
@@ -92,9 +92,6 @@ The following global flags may only be set in the global section
   per-module sections in the config file that didn't match any
   files processed in the current run.
 
-- ``strict_optional`` (Boolean, default False) enables experimental
-  strict Optional checks.
-
 - ``scripts_are_modules`` (Boolean, default False) makes script ``x``
   become module ``x`` instead of ``__main__``.  This is useful when
   checking multiple scripts in a single run.
@@ -180,6 +177,13 @@ overridden by the pattern sections matching the module name.
 - ``almost_silent`` (Boolean, deprecated) equivalent to
   ``follow_imports=skip``.
 
+- ``strict_optional`` (Boolean, default True) enables or disables
+  strict Optional checks. If False, mypy treats ``None`` as
+  compatible with every type.
+
+  **Note::** This was False by default
+  in mypy versions earlier than 0.600.
+
 - ``disallow_any_unimported`` (Boolean, default false) disallows usage of types that come
   from unfollowed imports (such types become aliases for ``Any``).