diff --git a/firebase-vertexai/api.txt b/firebase-vertexai/api.txt
index 7bb2f629c51..02faa3674a4 100644
--- a/firebase-vertexai/api.txt
+++ b/firebase-vertexai/api.txt
@@ -183,14 +183,14 @@ package com.google.firebase.vertexai.type {
   }
 
   public final class CountTokensResponse {
-    ctor public CountTokensResponse(int totalTokens, Integer? totalBillableCharacters = null, java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? promptTokensDetails = null);
+    ctor public CountTokensResponse(int totalTokens, Integer? totalBillableCharacters = null, java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> promptTokensDetails = emptyList());
     method public operator int component1();
     method public operator Integer? component2();
     method public operator java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? component3();
-    method public java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? getPromptTokensDetails();
+    method public java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> getPromptTokensDetails();
     method public Integer? getTotalBillableCharacters();
     method public int getTotalTokens();
-    property public final java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? promptTokensDetails;
+    property public final java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> promptTokensDetails;
     property public final Integer? totalBillableCharacters;
     property public final int totalTokens;
   }
@@ -582,16 +582,16 @@ package com.google.firebase.vertexai.type {
   }
 
   public final class UsageMetadata {
-    ctor public UsageMetadata(int promptTokenCount, Integer? candidatesTokenCount, int totalTokenCount, java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? promptTokensDetails, java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? candidatesTokensDetails);
+    ctor public UsageMetadata(int promptTokenCount, Integer? candidatesTokenCount, int totalTokenCount, java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> promptTokensDetails, java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> candidatesTokensDetails);
     method public Integer? getCandidatesTokenCount();
-    method public java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? getCandidatesTokensDetails();
+    method public java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> getCandidatesTokensDetails();
     method public int getPromptTokenCount();
-    method public java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? getPromptTokensDetails();
+    method public java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> getPromptTokensDetails();
     method public int getTotalTokenCount();
     property public final Integer? candidatesTokenCount;
-    property public final java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? candidatesTokensDetails;
+    property public final java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> candidatesTokensDetails;
     property public final int promptTokenCount;
-    property public final java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount>? promptTokensDetails;
+    property public final java.util.List<com.google.firebase.vertexai.type.ModalityTokenCount> promptTokensDetails;
     property public final int totalTokenCount;
   }
 
diff --git a/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/CountTokensResponse.kt b/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/CountTokensResponse.kt
index a6fe492862b..49f6b0433e0 100644
--- a/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/CountTokensResponse.kt
+++ b/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/CountTokensResponse.kt
@@ -36,7 +36,7 @@ import kotlinx.serialization.Serializable
 public class CountTokensResponse(
   public val totalTokens: Int,
   public val totalBillableCharacters: Int? = null,
-  public val promptTokensDetails: List<ModalityTokenCount>? = null,
+  public val promptTokensDetails: List<ModalityTokenCount> = emptyList(),
 ) {
   public operator fun component1(): Int = totalTokens
 
@@ -55,7 +55,7 @@ public class CountTokensResponse(
       return CountTokensResponse(
         totalTokens,
         totalBillableCharacters ?: 0,
-        promptTokensDetails?.map { it.toPublic() }
+        promptTokensDetails?.map { it.toPublic() } ?: emptyList()
       )
     }
   }
diff --git a/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/UsageMetadata.kt b/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/UsageMetadata.kt
index 5ebbc3639d9..16200792f9c 100644
--- a/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/UsageMetadata.kt
+++ b/firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/UsageMetadata.kt
@@ -33,8 +33,8 @@ public class UsageMetadata(
   public val promptTokenCount: Int,
   public val candidatesTokenCount: Int?,
   public val totalTokenCount: Int,
-  public val promptTokensDetails: List<ModalityTokenCount>?,
-  public val candidatesTokensDetails: List<ModalityTokenCount>?,
+  public val promptTokensDetails: List<ModalityTokenCount>,
+  public val candidatesTokensDetails: List<ModalityTokenCount>,
 ) {
 
   @Serializable
@@ -51,8 +51,8 @@ public class UsageMetadata(
         promptTokenCount ?: 0,
         candidatesTokenCount ?: 0,
         totalTokenCount ?: 0,
-        promptTokensDetails = promptTokensDetails?.map { it.toPublic() },
-        candidatesTokensDetails = candidatesTokensDetails?.map { it.toPublic() }
+        promptTokensDetails = promptTokensDetails?.map { it.toPublic() } ?: emptyList(),
+        candidatesTokensDetails = candidatesTokensDetails?.map { it.toPublic() } ?: emptyList()
       )
   }
 }
diff --git a/firebase-vertexai/src/test/java/com/google/firebase/vertexai/UnarySnapshotTests.kt b/firebase-vertexai/src/test/java/com/google/firebase/vertexai/UnarySnapshotTests.kt
index e176fd8f7eb..11d5a0df052 100644
--- a/firebase-vertexai/src/test/java/com/google/firebase/vertexai/UnarySnapshotTests.kt
+++ b/firebase-vertexai/src/test/java/com/google/firebase/vertexai/UnarySnapshotTests.kt
@@ -289,6 +289,7 @@ internal class UnarySnapshotTests {
         response.candidates.first().finishReason shouldBe FinishReason.STOP
         response.usageMetadata shouldNotBe null
         response.usageMetadata?.totalTokenCount shouldBe 363
+        response.usageMetadata?.promptTokensDetails?.isEmpty() shouldBe true
       }
     }
 
@@ -478,6 +479,7 @@ internal class UnarySnapshotTests {
 
         response.totalTokens shouldBe 6
         response.totalBillableCharacters shouldBe 16
+        response.promptTokensDetails.isEmpty() shouldBe true
       }
     }