diff --git a/FirebaseVertexAI/CHANGELOG.md b/FirebaseVertexAI/CHANGELOG.md
index 25f3f3181e0..9a7d5c70e7c 100644
--- a/FirebaseVertexAI/CHANGELOG.md
+++ b/FirebaseVertexAI/CHANGELOG.md
@@ -31,6 +31,9 @@
 - [changed] The default request timeout is now 180 seconds instead of the
   platform-default value of 60 seconds for a `URLRequest`; this timeout may
   still be customized in `RequestOptions`. (#13722)
+- [changed] The response from `GenerativeModel.countTokens(...)` now includes
+  `systemInstruction`, `tools` and `generationConfig` in the `totalTokens` and
+  `totalBillableCharacters` counts, where applicable. (#13813)
 
 # 11.3.0
 - [added] Added `Decodable` conformance for `FunctionResponse`. (#13606)
diff --git a/FirebaseVertexAI/Sources/CountTokensRequest.swift b/FirebaseVertexAI/Sources/CountTokensRequest.swift
index 6b052da19e6..128cb3b8ce6 100644
--- a/FirebaseVertexAI/Sources/CountTokensRequest.swift
+++ b/FirebaseVertexAI/Sources/CountTokensRequest.swift
@@ -17,7 +17,12 @@ import Foundation
 @available(iOS 15.0, macOS 11.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 struct CountTokensRequest {
   let model: String
+
   let contents: [ModelContent]
+  let systemInstruction: ModelContent?
+  let tools: [Tool]?
+  let generationConfig: GenerationConfig?
+
   let options: RequestOptions
 }
 
@@ -49,6 +54,9 @@ public struct CountTokensResponse {
 extension CountTokensRequest: Encodable {
   enum CodingKeys: CodingKey {
     case contents
+    case systemInstruction
+    case tools
+    case generationConfig
   }
 }
 
diff --git a/FirebaseVertexAI/Sources/GenerativeModel.swift b/FirebaseVertexAI/Sources/GenerativeModel.swift
index a5a8933e435..dc069d88d03 100644
--- a/FirebaseVertexAI/Sources/GenerativeModel.swift
+++ b/FirebaseVertexAI/Sources/GenerativeModel.swift
@@ -272,6 +272,9 @@ public final class GenerativeModel {
     let countTokensRequest = try CountTokensRequest(
       model: modelResourceName,
       contents: content(),
+      systemInstruction: systemInstruction,
+      tools: tools,
+      generationConfig: generationConfig,
       options: requestOptions
     )
     return try await generativeAIService.loadRequest(request: countTokensRequest)
diff --git a/FirebaseVertexAI/Tests/Integration/IntegrationTests.swift b/FirebaseVertexAI/Tests/Integration/IntegrationTests.swift
index 44eac05be22..0ccbb98e83a 100644
--- a/FirebaseVertexAI/Tests/Integration/IntegrationTests.swift
+++ b/FirebaseVertexAI/Tests/Integration/IntegrationTests.swift
@@ -19,7 +19,16 @@ import XCTest
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 final class IntegrationTests: XCTestCase {
   // Set temperature, topP and topK to lowest allowed values to make responses more deterministic.
-  let generationConfig = GenerationConfig(temperature: 0.0, topP: 0.0, topK: 1)
+  let generationConfig = GenerationConfig(
+    temperature: 0.0,
+    topP: 0.0,
+    topK: 1,
+    responseMIMEType: "text/plain"
+  )
+  let systemInstruction = ModelContent(
+    role: "system",
+    parts: "You are a friendly and helpful assistant."
+  )
 
   var vertex: VertexAI!
   var model: GenerativeModel!
@@ -40,7 +49,9 @@ final class IntegrationTests: XCTestCase {
     vertex = VertexAI.vertexAI()
     model = vertex.generativeModel(
       modelName: "gemini-1.5-flash",
-      generationConfig: generationConfig
+      generationConfig: generationConfig,
+      tools: [],
+      systemInstruction: systemInstruction
     )
   }
 
@@ -68,7 +79,7 @@ final class IntegrationTests: XCTestCase {
 
     let response = try await model.countTokens(prompt)
 
-    XCTAssertEqual(response.totalTokens, 6)
-    XCTAssertEqual(response.totalBillableCharacters, 16)
+    XCTAssertEqual(response.totalTokens, 14)
+    XCTAssertEqual(response.totalBillableCharacters, 51)
   }
 }
diff --git a/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift b/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift
index 6956160b072..c5e8332d2b8 100644
--- a/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift
+++ b/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift
@@ -1234,6 +1234,48 @@ final class GenerativeModelTests: XCTestCase {
     XCTAssertEqual(response.totalBillableCharacters, 16)
   }
 
+  func testCountTokens_succeeds_allOptions() async throws {
+    MockURLProtocol.requestHandler = try httpRequestHandler(
+      forResource: "unary-success-total-tokens",
+      withExtension: "json"
+    )
+    let generationConfig = GenerationConfig(
+      temperature: 0.5,
+      topP: 0.9,
+      topK: 3,
+      candidateCount: 1,
+      maxOutputTokens: 1024,
+      stopSequences: ["test-stop"],
+      responseMIMEType: "text/plain"
+    )
+    let sumFunction = FunctionDeclaration(
+      name: "sum",
+      description: "Add two integers.",
+      parameters: ["x": .integer(), "y": .integer()]
+    )
+    let systemInstruction = ModelContent(
+      role: "system",
+      parts: "You are a calculator. Use the provided tools."
+    )
+    model = GenerativeModel(
+      name: testModelResourceName,
+      projectID: "my-project-id",
+      apiKey: "API_KEY",
+      generationConfig: generationConfig,
+      tools: [Tool(functionDeclarations: [sumFunction])],
+      systemInstruction: systemInstruction,
+      requestOptions: RequestOptions(),
+      appCheck: nil,
+      auth: nil,
+      urlSession: urlSession
+    )
+
+    let response = try await model.countTokens("Why is the sky blue?")
+
+    XCTAssertEqual(response.totalTokens, 6)
+    XCTAssertEqual(response.totalBillableCharacters, 16)
+  }
+
   func testCountTokens_succeeds_noBillableCharacters() async throws {
     MockURLProtocol.requestHandler = try httpRequestHandler(
       forResource: "unary-success-no-billable-characters",