diff --git a/CHANGELOG.md b/CHANGELOG.md
index 76552471e..175a57036 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ Changelog
 
 ### Enhancements
 
+* Add internal api for mutating session payload before sending
+  [#341](https://github.com/bugsnag/bugsnag-cocoa/pull/341)
+
 * Persist breadcrumbs on disk to allow reading upon next boot in the event of an
   uncatchable app termination.
 * Add `+[Bugsnag appDidCrashLastLaunch]` as a helper to determine if the
diff --git a/Source/BugsnagKSCrashSysInfoParser.m b/Source/BugsnagKSCrashSysInfoParser.m
index 59a5a5ea0..354f8a784 100644
--- a/Source/BugsnagKSCrashSysInfoParser.m
+++ b/Source/BugsnagKSCrashSysInfoParser.m
@@ -118,7 +118,13 @@
     BSGDictSetSafeObject(deviceState, report[@"machine"], @"model");
     BSGDictSetSafeObject(deviceState, report[@"system_name"], @"osName");
     BSGDictSetSafeObject(deviceState, report[@"system_version"], @"osVersion");
-    BSGDictSetSafeObject(deviceState, report[@"os_version"], @"osBuild");
+
+    NSString *osVersion = report[@"os_version"];
+
+    if (osVersion != nil) {
+        BSGDictSetSafeObject(deviceState, @{@"osBuild": osVersion}, @"runtimeVersions");
+    }
+
     BSGDictSetSafeObject(deviceState, @(PLATFORM_WORD_SIZE), @"wordSize");
     BSGDictSetSafeObject(deviceState, @"Apple", @"manufacturer");
     BSGDictSetSafeObject(deviceState, report[@"jailbroken"], @"jailbroken");
diff --git a/Tests/BugsnagSinkTests.m b/Tests/BugsnagSinkTests.m
index b783f0c8b..bddbc6e13 100644
--- a/Tests/BugsnagSinkTests.m
+++ b/Tests/BugsnagSinkTests.m
@@ -270,7 +270,7 @@ - (void)testEventDevice {
     XCTAssertEqualObjects(device[@"modelNumber"], @"MacBookPro11,3");
     XCTAssertEqualObjects(device[@"osName"], @"iPhone OS");
     XCTAssertEqualObjects(device[@"osVersion"], @"8.1");
-    XCTAssertEqualObjects(device[@"osBuild"], @"14B25");
+    XCTAssertEqualObjects(device[@"runtimeVersions"][@"osBuild"], @"14B25");
     XCTAssertEqualObjects(device[@"totalMemory"], @15065522176);
     XCTAssertNotNil(device[@"freeDisk"]);
     XCTAssertEqualObjects(device[@"timezone"], @"PST");
diff --git a/features/runtime_versions.feature b/features/runtime_versions.feature
new file mode 100644
index 000000000..1fa7adafb
--- /dev/null
+++ b/features/runtime_versions.feature
@@ -0,0 +1,14 @@
+Feature: Runtime versions are included in all requests
+
+Scenario: Runtime versions included in Cocoa error
+    When I run "HandledErrorScenario"
+    Then I should receive a request
+    And the request is valid for the error reporting API
+    And the payload field "events.0.device.runtimeVersions.osBuild" is not null
+
+Scenario: Runtime versions included in Cocoa session
+    When I run "ManualSessionScenario"
+    And I wait for 10 seconds
+    Then I should receive a request
+    And the request is a valid for the session tracking API
+    And the payload field "device.runtimeVersions.osBuild" is not null