diff --git a/FirebaseVertexAI/CHANGELOG.md b/FirebaseVertexAI/CHANGELOG.md
index 1332b53f7e1..3a194a4a8b4 100644
--- a/FirebaseVertexAI/CHANGELOG.md
+++ b/FirebaseVertexAI/CHANGELOG.md
@@ -36,6 +36,9 @@
   as input. (#13767)
 - [changed] **Breaking Change**: All initializers for `ModelContent` now require
   the label `parts: `. (#13832)
+- [changed] **Breaking Change**: `HarmCategory` is now a struct instead of an
+  enum type and the `unknown` case has been removed; in a `switch` statement,
+  use the `default:` case to cover unknown or unhandled categories. (#13728)
 - [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)
diff --git a/FirebaseVertexAI/Sample/ChatSample/Views/ErrorDetailsView.swift b/FirebaseVertexAI/Sample/ChatSample/Views/ErrorDetailsView.swift
index 4bc18345cfb..ff6807a84b4 100644
--- a/FirebaseVertexAI/Sample/ChatSample/Views/ErrorDetailsView.swift
+++ b/FirebaseVertexAI/Sample/ChatSample/Views/ErrorDetailsView.swift
@@ -23,7 +23,9 @@ extension HarmCategory: CustomStringConvertible {
     case .harassment: "Harassment"
     case .hateSpeech: "Hate speech"
     case .sexuallyExplicit: "Sexually explicit"
-    case .unknown: "Unknown"
+    case .civicIntegrity: "Civic integrity"
+    default:
+      "Unknown HarmCategory: \(rawValue)"
     }
   }
 }
diff --git a/FirebaseVertexAI/Sources/Safety.swift b/FirebaseVertexAI/Sources/Safety.swift
index a57900e7317..3f6ce4658c1 100644
--- a/FirebaseVertexAI/Sources/Safety.swift
+++ b/FirebaseVertexAI/Sources/Safety.swift
@@ -97,21 +97,65 @@ public struct SafetySetting {
 }
 
 /// Categories describing the potential harm a piece of content may pose.
-public enum HarmCategory: String, Sendable {
-  /// Unknown. A new server value that isn't recognized by the SDK.
-  case unknown = "HARM_CATEGORY_UNKNOWN"
+public struct HarmCategory: Sendable, Equatable, Hashable {
+  enum Kind: String {
+    case harassment = "HARM_CATEGORY_HARASSMENT"
+    case hateSpeech = "HARM_CATEGORY_HATE_SPEECH"
+    case sexuallyExplicit = "HARM_CATEGORY_SEXUALLY_EXPLICIT"
+    case dangerousContent = "HARM_CATEGORY_DANGEROUS_CONTENT"
+    case civicIntegrity = "HARM_CATEGORY_CIVIC_INTEGRITY"
+  }
 
   /// Harassment content.
-  case harassment = "HARM_CATEGORY_HARASSMENT"
+  public static var harassment: HarmCategory {
+    return self.init(kind: .harassment)
+  }
 
   /// Negative or harmful comments targeting identity and/or protected attributes.
-  case hateSpeech = "HARM_CATEGORY_HATE_SPEECH"
+  public static var hateSpeech: HarmCategory {
+    return self.init(kind: .hateSpeech)
+  }
 
   /// Contains references to sexual acts or other lewd content.
-  case sexuallyExplicit = "HARM_CATEGORY_SEXUALLY_EXPLICIT"
+  public static var sexuallyExplicit: HarmCategory {
+    return self.init(kind: .sexuallyExplicit)
+  }
 
   /// Promotes or enables access to harmful goods, services, or activities.
-  case dangerousContent = "HARM_CATEGORY_DANGEROUS_CONTENT"
+  public static var dangerousContent: HarmCategory {
+    return self.init(kind: .dangerousContent)
+  }
+
+  /// Content that may be used to harm civic integrity.
+  public static var civicIntegrity: HarmCategory {
+    return self.init(kind: .civicIntegrity)
+  }
+
+  /// Returns the raw string representation of the `HarmCategory` value.
+  ///
+  /// > Note: This value directly corresponds to the values in the
+  /// > [REST API](https://cloud.google.com/vertex-ai/docs/reference/rest/v1beta1/HarmCategory).
+  public let rawValue: String
+
+  init(kind: Kind) {
+    rawValue = kind.rawValue
+  }
+
+  init(rawValue: String) {
+    if Kind(rawValue: rawValue) == nil {
+      VertexLog.error(
+        code: .generateContentResponseUnrecognizedHarmCategory,
+        """
+        Unrecognized HarmCategory with value "\(rawValue)":
+        - Check for updates to the SDK as support for "\(rawValue)" may have been added; see \
+        release notes at https://firebase.google.com/support/release-notes/ios
+        - Search for "\(rawValue)" in the Firebase Apple SDK Issue Tracker at \
+        https://github.com/firebase/firebase-ios-sdk/issues and file a Bug Report if none found
+        """
+      )
+    }
+    self.rawValue = rawValue
+  }
 }
 
 // MARK: - Codable Conformances
@@ -139,17 +183,8 @@ extension SafetyRating: Decodable {}
 @available(iOS 15.0, macOS 11.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 extension HarmCategory: Codable {
   public init(from decoder: Decoder) throws {
-    let value = try decoder.singleValueContainer().decode(String.self)
-    guard let decodedCategory = HarmCategory(rawValue: value) else {
-      VertexLog.error(
-        code: .generateContentResponseUnrecognizedHarmCategory,
-        "Unrecognized HarmCategory with value \"\(value)\"."
-      )
-      self = .unknown
-      return
-    }
-
-    self = decodedCategory
+    let rawValue = try decoder.singleValueContainer().decode(String.self)
+    self = HarmCategory(rawValue: rawValue)
   }
 }
 
diff --git a/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift b/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift
index 86d3e7f9c11..254f81e96fb 100644
--- a/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift
+++ b/FirebaseVertexAI/Tests/Unit/GenerativeModelTests.swift
@@ -163,7 +163,7 @@ final class GenerativeModelTests: XCTestCase {
     let expectedSafetyRatings = [
       SafetyRating(category: .harassment, probability: .medium),
       SafetyRating(category: .dangerousContent, probability: .unknown),
-      SafetyRating(category: .unknown, probability: .high),
+      SafetyRating(category: HarmCategory(rawValue: "FAKE_NEW_HARM_CATEGORY"), probability: .high),
     ]
     MockURLProtocol
       .requestHandler = try httpRequestHandler(
@@ -972,18 +972,22 @@ final class GenerativeModelTests: XCTestCase {
         forResource: "streaming-success-unknown-safety-enum",
         withExtension: "txt"
       )
+    let unknownSafetyRating = SafetyRating(
+      category: HarmCategory(rawValue: "HARM_CATEGORY_DANGEROUS_CONTENT_NEW_ENUM"),
+      probability: .unknown
+    )
 
-    var hadUnknown = false
+    var foundUnknownSafetyRating = false
     let stream = try model.generateContentStream("Hi")
     for try await content in stream {
       XCTAssertNotNil(content.text)
       if let ratings = content.candidates.first?.safetyRatings,
-         ratings.contains(where: { $0.category == .unknown }) {
-        hadUnknown = true
+         ratings.contains(where: { $0 == unknownSafetyRating }) {
+        foundUnknownSafetyRating = true
       }
     }
 
-    XCTAssertTrue(hadUnknown)
+    XCTAssertTrue(foundUnknownSafetyRating)
   }
 
   func testGenerateContentStream_successWithCitations() async throws {