diff --git a/core/src/main/java/com/segment/analytics/kotlin/core/HTTPClient.kt b/core/src/main/java/com/segment/analytics/kotlin/core/HTTPClient.kt
index c9e21772..f3d25a15 100644
--- a/core/src/main/java/com/segment/analytics/kotlin/core/HTTPClient.kt
+++ b/core/src/main/java/com/segment/analytics/kotlin/core/HTTPClient.kt
@@ -1,7 +1,6 @@
 package com.segment.analytics.kotlin.core
 
 import com.segment.analytics.kotlin.core.Constants.LIBRARY_VERSION
-import com.segment.analytics.kotlin.core.utilities.encodeToBase64
 import java.io.BufferedReader
 import java.io.Closeable
 import java.io.IOException
@@ -12,7 +11,6 @@ import java.net.MalformedURLException
 import java.net.URL
 import java.util.zip.GZIPOutputStream
 class HTTPClient(private val writeKey: String) {
-    internal val authHeader = authorizationHeader(writeKey)
 
     fun settings(cdnHost: String): Connection {
         val connection: HttpURLConnection =
@@ -29,7 +27,6 @@ class HTTPClient(private val writeKey: String) {
     fun upload(apiHost: String): Connection {
         val connection: HttpURLConnection = openConnection("https://$apiHost/b")
         connection.setRequestProperty("Content-Type", "text/plain")
-        connection.setRequestProperty("Authorization", authHeader)
         connection.doOutput = true
         connection.setChunkedStreamingMode(0)
         return connection.createPostConnection()
@@ -56,11 +53,6 @@ class HTTPClient(private val writeKey: String) {
         connection.doInput = true
         return connection
     }
-
-    private fun authorizationHeader(writeKey: String): String {
-        val auth = "$writeKey:"
-        return "Basic ${encodeToBase64(auth)}"
-    }
 }
 
 /**
diff --git a/core/src/main/java/com/segment/analytics/kotlin/core/platform/plugins/ContextPlugin.kt b/core/src/main/java/com/segment/analytics/kotlin/core/platform/plugins/ContextPlugin.kt
index add23abf..d7e7d1d8 100644
--- a/core/src/main/java/com/segment/analytics/kotlin/core/platform/plugins/ContextPlugin.kt
+++ b/core/src/main/java/com/segment/analytics/kotlin/core/platform/plugins/ContextPlugin.kt
@@ -8,6 +8,7 @@ import com.segment.analytics.kotlin.core.utilities.putAll
 import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.buildJsonObject
 import kotlinx.serialization.json.put
+import java.util.*
 
 /**
  * Analytics plugin used to populate events with basic context data.
@@ -18,12 +19,14 @@ class ContextPlugin : Plugin {
     override lateinit var analytics: Analytics
 
     private lateinit var library: JsonObject
+    private val instanceId = UUID.randomUUID().toString()
 
     companion object {
         // Library
         const val LIBRARY_KEY = "library"
         const val LIBRARY_NAME_KEY = "name"
         const val LIBRARY_VERSION_KEY = "version"
+        const val INSTANCE_ID_KEY = "instanceId"
     }
 
     override fun setup(analytics: Analytics) {
@@ -41,6 +44,7 @@ class ContextPlugin : Plugin {
 
             // putLibrary
             put(LIBRARY_KEY, library)
+            put(INSTANCE_ID_KEY, instanceId)
         }
         event.context = newContext
     }
diff --git a/core/src/test/kotlin/com/segment/analytics/kotlin/core/AnalyticsTests.kt b/core/src/test/kotlin/com/segment/analytics/kotlin/core/AnalyticsTests.kt
index ec02d85e..7ea3556c 100644
--- a/core/src/test/kotlin/com/segment/analytics/kotlin/core/AnalyticsTests.kt
+++ b/core/src/test/kotlin/com/segment/analytics/kotlin/core/AnalyticsTests.kt
@@ -47,6 +47,7 @@ class AnalyticsTests {
             put(ContextPlugin.LIBRARY_VERSION_KEY, Constants.LIBRARY_VERSION)
         }
         put(ContextPlugin.LIBRARY_KEY, lib)
+        put(ContextPlugin.INSTANCE_ID_KEY, "qwerty-qwerty-123")
     }
 
     private val testDispatcher = UnconfinedTestDispatcher()
diff --git a/core/src/test/kotlin/com/segment/analytics/kotlin/core/HTTPClientTests.kt b/core/src/test/kotlin/com/segment/analytics/kotlin/core/HTTPClientTests.kt
index 4f33f1a6..c5ee104a 100644
--- a/core/src/test/kotlin/com/segment/analytics/kotlin/core/HTTPClientTests.kt
+++ b/core/src/test/kotlin/com/segment/analytics/kotlin/core/HTTPClientTests.kt
@@ -80,9 +80,4 @@ class HTTPClientTests {
         }
     }
 
-    @Test
-    fun `authHeader is correctly computed`() {
-        assertEquals("Basic MXZOZ1Vxd0plQ0htcWdJOVMxc09tOVVIQ3lmWXFiYVE6", httpClient.authHeader)
-    }
-
 }
\ No newline at end of file
diff --git a/core/src/test/kotlin/com/segment/analytics/kotlin/core/compat/JavaAnalyticsTest.kt b/core/src/test/kotlin/com/segment/analytics/kotlin/core/compat/JavaAnalyticsTest.kt
index 6aa5e658..4f655141 100644
--- a/core/src/test/kotlin/com/segment/analytics/kotlin/core/compat/JavaAnalyticsTest.kt
+++ b/core/src/test/kotlin/com/segment/analytics/kotlin/core/compat/JavaAnalyticsTest.kt
@@ -53,6 +53,7 @@ internal class JavaAnalyticsTest {
             put(ContextPlugin.LIBRARY_VERSION_KEY, Constants.LIBRARY_VERSION)
         }
         put(ContextPlugin.LIBRARY_KEY, lib)
+        put(ContextPlugin.INSTANCE_ID_KEY, "qwerty-qwerty-123")
     }
 
     private val testDispatcher = UnconfinedTestDispatcher()