diff --git a/api_core/CHANGELOG.md b/api_core/CHANGELOG.md
index 0d601ee6b85d..890d88e043d2 100644
--- a/api_core/CHANGELOG.md
+++ b/api_core/CHANGELOG.md
@@ -4,24 +4,21 @@
 
 [1]: https://pypi.org/project/google-api-core/#history
 
-## 1.6.0a1
+## 1.5.1
 
-10-18-2018 16:26 PDT
+10-29-2018 13:29 PDT
 
-### New Features
-- Add methods to api_core used by new autogenerator. ([#6267](https://github.com/googleapis/google-cloud-python/pull/6267))
+### Implementation Changes
+- Don't URL-encode slashes in gRPC request headers. ([#6310](https://github.com/googleapis/google-cloud-python/pull/6310))
 
 ### Internal / Testing Changes
-- Fix branch coverage for un-called callbacks. ([#6242](https://github.com/googleapis/google-cloud-python/pull/6242))
-- Fix import order, appeasing lint. ([#6240](https://github.com/googleapis/google-cloud-python/pull/6240))
-- Add / fix badges for PyPI / versions. ([#6158](https://github.com/googleapis/google-cloud-python/pull/6158))
+- Back out changes from [#6267](https://github.com/googleapis/google-cloud-python/pull/6267) / `api_core-1.6.0a1` release. ([#6328](https://github.com/googleapis/google-cloud-python/pull/6328))
 
 ## 1.5.0
 
 ### New Features
 - Add bidi, Bidirection Streaming, to api-core ([#6211](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/6211))
 
-
 ### Internal / Testing Changes
 - Use new Nox ([#6175](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/6175))
 
diff --git a/api_core/setup.py b/api_core/setup.py
index 82668b39ead5..fdff7c34d92a 100644
--- a/api_core/setup.py
+++ b/api_core/setup.py
@@ -22,7 +22,7 @@
 
 name = 'google-api-core'
 description = 'Google API client core library'
-version = '1.6.0a1'
+version = '1.5.1'
 # Should be one of:
 # 'Development Status :: 3 - Alpha'
 # 'Development Status :: 4 - Beta'