[Firebase AI] Deprecate TotalBillableCharacters (#1283)

* [Firebase AI] Deprecate TotalBillableCharacters

* Update CountTokensResponse.cs

Author: a-maurice

docs/readme.md

@@ -115,6 +115,8 @@ Release Notes
     - Analytics: Removed deprecated `FirebaseAnalytics.ParameterGroupId`
       and `Parameter.Dispose` methods.
     - Auth: Removed deprecated `FirebaseUser.UpdateEmailAsync`.
+    - Firebase AI: Deprecated `CountTokensResponse.TotalBillableCharacters`, use
+      `CountTokensResponse.TotalTokens` instead.
     - Messaging: Removed deprecated `FirebaseMessage.Dispose`,
       `FirebaseNotification.Dispose`, and `MessagingOptions.Dispose` methods.
 

firebaseai/src/CountTokensResponse.cs

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using Google.MiniJSON;
@@ -35,6 +36,12 @@ public readonly struct CountTokensResponse {
   /// > Important: This does not include billable image, video or other non-text input. See
   /// [Firebase AI pricing](https://firebase.google.com/docs/vertex-ai/pricing) for details.
   /// </summary>
+  /// <remarks>
+  /// Use TotalTokens instead; Gemini 2.0 series models and newer are always billed by token count.
+  /// </remarks>
+  /// @deprecated Use TotalTokens instead; Gemini 2.0 series models and newer are always
+  /// billed by token count.
+  [Obsolete("Use TotalTokens instead; Gemini 2.0 series models and newer are always billed by token count.")]
   public int? TotalBillableCharacters { get; }
 
   private readonly ReadOnlyCollection<ModalityTokenCount> _promptTokensDetails;
@@ -52,7 +59,9 @@ private CountTokensResponse(int totalTokens,
                               int? totalBillableCharacters = null,
                               List<ModalityTokenCount> promptTokensDetails = null) {
     TotalTokens = totalTokens;
+#pragma warning disable CS0618
     TotalBillableCharacters = totalBillableCharacters;
+#pragma warning restore CS0618
     _promptTokensDetails =
         new ReadOnlyCollection<ModalityTokenCount>(promptTokensDetails ?? new List<ModalityTokenCount>());
   }

firebaseai/testapp/Assets/Firebase/Sample/FirebaseAI/UIHandlerAutomated.cs

@@ -627,11 +627,6 @@ async Task TestCountTokens(Backend backend) {
       CountTokensResponse response = await model.CountTokensAsync("Hello, I am testing CountTokens!");
 
       Assert($"CountTokens TotalTokens {response.TotalTokens}", response.TotalTokens > 0);
-      // TotalBillableCharacters is only expected to be set with VertexAI.
-      if (backend == Backend.VertexAI) {
-        Assert($"CountTokens TotalBillableCharacters {response.TotalBillableCharacters}",
-              response.TotalBillableCharacters > 0);
-      }
 
       AssertEq("CountTokens PromptTokenDetails", response.PromptTokensDetails.Count(), 1);
       var details = response.PromptTokensDetails.First();
@@ -1014,7 +1009,9 @@ async Task InternalTestCountTokenResponse() {
       CountTokensResponse response = CountTokensResponse.FromJson(json);
 
       AssertEq("TotalTokens", response.TotalTokens, 1837);
+#pragma warning disable CS0618
       AssertEq("TotalBillableCharacters", response.TotalBillableCharacters, 117);
+#pragma warning restore CS0618
       List<ModalityTokenCount> details = response.PromptTokensDetails.ToList();
       AssertEq("PromptTokensDetails.Count", details.Count, 2);
       AssertEq("PromptTokensDetails[0].Modality", details[0].Modality, ContentModality.Image);