Updated release notes for HttpCore 5.1-beta3 release
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index 91558f2..b95ed76 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -1,3 +1,63 @@
+Release 5.1 BETA3
+------------------
+
+This is likely the last BETA release in the 5.1 release series. The next release is
+expected to be 5.1 GA. This beta includes a number of new features as well as
+bug fixes from the stable 5.0.x branch.
+
+Notable changes and features included in the 5.1 series:
+
+* Conditional conformance with RFC 3986 (Uniform Resource Identifier (URI): Generic Syntax).
+
+* Improved support for out of sequence response message handing by the the classic (blocking)
+ HTTP transport.
+
+
+Change Log
+-------------------
+
+* RFC 3986 conformance: Added `#normalizeSyntax` method to URIBuilder.
+ Contributed by Oleg Kalnichevski <olegk at apache.org>
+
+* HTTPCORE-663: Added http status code 425.
+ Contributed by Arturo Bernal <arturobernalg at gmail.com>
+
+* HTTPCORE-661: Added http status code 426.
+ Contributed by Arturo Bernal <arturobernalg at gmail.com>
+
+* HTTPCORE-659: Fixed race condition in IOSessionImpl when setting event.
+ Contributed by Nicolas Capponi <nicolas.capponi at forgerock.com>
+
+* HTTPCORE-658: Removed explicit inbound / outbound socket shutdown from
+ the `#close` method of classic HTTP connections.
+ Contributed by Oleg Kalnichevski <olegk at apache.org>
+
+* HTTPCORE-657: Added TrafficClass to IOReactorConfig (#243).
+ Contributed by Desmond Yeung <dyeung at datto.com>
+
+* Add filters before MAIN_HANDLER so they won't be ignored (#236).
+ Contributed by Rob Spoor <robtimus at users.noreply.github.com>
+
+* Bug fix: Fixed broken result callback in ProtocolNegotiatorBase.
+ Contributed by Oleg Kalnichevski <olegk at apache.org>
+
+* Fixed NPE and improve code centralization in URIBuilder (#235).
+ Contributed by Lars Helge Øverland <lars at dhis2.org>
+
+* Added `#appendPath` and `#appendPathSegments` methods to URIBuilder (#234).
+ Contributed by Lars Helge Øverland <lars at dhis2.org>
+
+* Removed connection acceptor API changes (moved to 5.2).
+ Contributed by Oleg Kalnichevski <olegk at apache.org>
+
+* Removed protocol upgrade API changes (moved to 5.2).
+ Contributed by Oleg Kalnichevski <olegk at apache.org>
+
+* Bug fix: Do not attempt to shut down non-blocking TLS session gracefully
+ in case the TLS handshake has not been fully completed.
+ Contributed by Oleg Kalnichevski <olegk@apache.org>
+
+
Release 5.1 BETA2
------------------
