diff --git a/src/Language/LanguageClient.php b/src/Language/LanguageClient.php
index 8250dcbe299e..bda227a246d1 100644
--- a/src/Language/LanguageClient.php
+++ b/src/Language/LanguageClient.php
@@ -66,11 +66,13 @@ class LanguageClient
     /**
      * Create a Language client.
      *
+     * Note that when creating a LanguageClient instance, setting
+     * `$config.projectId` is not supported. To switch between projects, you
+     * must provide credentials with access to the project.
+     *
      * @param array $config [optional] {
      *     Configuration Options.
      *
-     *     @type string $projectId The project ID from the Google Developer's
-     *           Console.
      *     @type CacheItemPoolInterface $authCache A cache for storing access
      *           tokens. **Defaults to** a simple in memory implementation.
      *     @type array $authCacheOptions Cache configuration options.
diff --git a/src/Speech/SpeechClient.php b/src/Speech/SpeechClient.php
index 94e81b46edb0..54b41ac9518e 100644
--- a/src/Speech/SpeechClient.php
+++ b/src/Speech/SpeechClient.php
@@ -59,11 +59,13 @@ class SpeechClient
     /**
      * Create a Speech client.
      *
+     * Note that when creating a SpeechClient instance, setting
+     * `$config.projectId` is not supported. To switch between projects, you
+     * must provide credentials with access to the project.
+     *
      * @param array $config [optional] {
      *     Configuration Options.
      *
-     *     @type string $projectId The project ID from the Google Developer's
-     *           Console.
      *     @type CacheItemPoolInterface $authCache A cache for storing access
      *           tokens. **Defaults to** a simple in memory implementation.
      *     @type array $authCacheOptions Cache configuration options.
diff --git a/src/Translate/TranslateClient.php b/src/Translate/TranslateClient.php
index d15c604513cd..67304f6dccb4 100644
--- a/src/Translate/TranslateClient.php
+++ b/src/Translate/TranslateClient.php
@@ -70,6 +70,10 @@ class TranslateClient
     /**
      * Create a Translate client.
      *
+     * Note that when creating a TranslateClient instance, setting
+     * `$config.projectId` is not supported. To switch between projects, you
+     * must provide credentials with access to the project.
+     *
      * @param array $config [optional] {
      *     Configuration Options.
      *
@@ -77,8 +81,6 @@ class TranslateClient
      *     @type string $target The target language to assign to the client.
      *           Must be a valid ISO 639-1 language code. **Defaults to** `"en"`
      *           (English).
-     *     @type string $projectId The project ID from the Google Developer's
-     *           Console.
      *     @type CacheItemPoolInterface $authCache A cache used storing access
      *           tokens. **Defaults to** a simple in memory implementation.
      *     @type array $authCacheOptions Cache configuration options.
diff --git a/src/Vision/VisionClient.php b/src/Vision/VisionClient.php
index 5c553a1b5b3d..abb5abbe8277 100644
--- a/src/Vision/VisionClient.php
+++ b/src/Vision/VisionClient.php
@@ -54,11 +54,13 @@ class VisionClient
     /**
      * Create a Vision client.
      *
+     * Note that when creating a VisionClient instance, setting
+     * `$config.projectId` is not supported. To switch between projects, you
+     * must provide credentials with access to the project.
+     *
      * @param array $config [optional] {
      *     Configuration Options.
      *
-     *     @type string $projectId The project ID from the Google Developer's
-     *           Console.
      *     @type CacheItemPoolInterface $authCache A cache for storing access
      *           tokens. **Defaults to** a simple in memory implementation.
      *     @type array $authCacheOptions Cache configuration options.