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Co-authored-by: Brett Graham <[email protected]>

README.rst

@@ -191,10 +191,10 @@ The `open` function also works as a context handler:
 
 .. warning::
     The ``copy_arrays`` argument of `asdf.open()` and `AsdfFile` is deprecated,
-    and will be removed in ASDF 4.0. It is replaced by the more-explicitly-named
-    ``memmap`` argument as the inverse of ``copy_arrays``
-    (``memmap == not copy_arrays``). Using ``copy_arrays`` will work for now, but
-    give an ``AsdfWarning``.
+    and will be removed in ASDF 4.0. It is replaced by ``memmap``, which
+    is the opposite of ``copy_arrays`` (``memmap == not copy_arrays``).
+    In ASDF 4.0, ``memmap`` will default to ``False``, which means arrays 
+    will no longer be memory-mapped by default.
 
 To get a quick overview of the data stored in the file, use the top-level
 `AsdfFile.info()` method:

asdf/_asdf.py

@@ -125,7 +125,7 @@ def __init__(
             When `True`, when reading files, attempt to memmap underlying data
             arrays when possible. When set, this argument will override
             ``copy_arrays``. The default will change to ``False`` in an upcoming
-            ASDF version.
+            ASDF version. At the moment the default is ``True``.
 
         lazy_load : bool, optional
             When `True` and the underlying file handle is seekable, data
@@ -1673,7 +1673,7 @@ def open_asdf(
         When `True`, when reading files, attempt to memmap underlying data
         arrays when possible. When set, this argument will override
         ``copy_arrays``. The default will change to ``False`` in an upcoming
-        ASDF version.
+        ASDF version. At the moment the default is ``True``.
 
     lazy_load : bool, optional
         When `True` and the underlying file handle is seekable, data