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diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index fc47c76e99..73896be453 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,2 +1,51 @@
+## Rails 6.0.0.alpha (Unreleased) ##
+
+*   Return all mappings for a timezone identifier in `country_zones`
+
+    Some timezones like `Europe/London` have multiple mappings in
+    `ActiveSupport::TimeZone::MAPPING` so return all of them instead
+    of the first one found by using `Hash#value`. e.g:
+
+        # Before
+        ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh"]
+
+        # After
+        ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh", "London"]
+
+    Fixes #31668.
+
+    *Andrew White*
+
+*   `String#truncate_bytes` to truncate a string to a maximum bytesize without
+    breaking multibyte characters or grapheme clusters like 👩‍👩‍👦‍👦.
+
+    *Jeremy Daer*
+
+*   `String#strip_heredoc` preserves frozenness.
+
+        "foo".freeze.strip_heredoc.frozen?  # => true
+
+    Fixes that frozen string literals would inadvertently become unfrozen:
+
+        # frozen_string_literal: true
+
+        foo = <<-MSG.strip_heredoc
+          la la la
+        MSG
+
+        foo.frozen?  # => false !??
+
+    *Jeremy Daer*
+
+*   Rails 6 requires Ruby 2.4.1 or newer.
+
+    *Jeremy Daer*
+
+*   Adds parallel testing to Rails
+
+    Parallelize your test suite with forked processes or threads.
+
+    *Eileen M. Uchitelle*, *Aaron Patterson*
+
 
 Please check [5-2-stable](https://github.com/rails/rails/blob/5-2-stable/activesupport/CHANGELOG.md) for previous changes.