feat(google_genai): add Gemma model family support

packages/genkit_google_genai/lib/genkit_google_genai.dart

@@ -32,6 +32,10 @@ class GoogleGenAiPluginHandle {
     return modelRef('googleai/$name', customOptions: GeminiOptions.$schema);
   }
 
+  ModelRef<GemmaOptions> gemma(String name) {
+    return modelRef('googleai/$name', customOptions: GemmaOptions.$schema);
+  }
+
   EmbedderRef<TextEmbedderOptions> textEmbedding(String name) {
     return embedderRef(
       'googleai/$name',

packages/genkit_google_genai/lib/src/common_plugin.dart

@@ -21,6 +21,7 @@ import 'package:schemantic/schemantic.dart';
 
 import 'aggregation.dart';
 import 'api_client.dart';
+import 'gemma.dart';
 import 'generated/generativelanguage.dart' as gcl;
 import 'model.dart';
 
@@ -40,11 +41,16 @@ final commonModelInfo = ModelInfo(
 abstract class CommonGoogleGenPlugin extends GenkitPlugin {
   Future<GenerativeLanguageBaseClient> getApiClient([String? requestApiKey]);
 
-  Model createModel(String modelName, SchemanticType customOptions) {
+  Model createModel(
+    String modelName,
+    SchemanticType customOptions, {
+    ModelInfo? modelInfo,
+  }) {
+    final isGemma = isGemmaModelName(modelName);
     return Model(
       name: '$name/$modelName',
       customOptions: customOptions,
-      metadata: {'model': commonModelInfo.toJson()},
+      metadata: {'model': (modelInfo ?? commonModelInfo).toJson()},
       fn: (req, ctx) async {
         gcl.GenerationConfig generationConfig;
         List<gcl.SafetySetting>? safetySettings;
@@ -74,9 +80,17 @@ abstract class CommonGoogleGenPlugin extends GenkitPlugin {
           );
           toolConfig = toGeminiToolConfig(options.functionCallingConfig);
         } else {
-          final options = req.config == null
-              ? GeminiOptions()
-              : GeminiOptions.$schema.parse(req.config!);
+          final GeminiOptions options;
+          if (isGemma) {
+            final gemmaOptions = req.config == null
+                ? GemmaOptions()
+                : GemmaOptions.$schema.parse(req.config!);
+            options = gemmaToGeminiOptions(gemmaOptions);
+          } else {
+            options = req.config == null
+                ? GeminiOptions()
+                : GeminiOptions.$schema.parse(req.config!);
+          }
           apiKey = options.apiKey;
           generationConfig = toGeminiSettings(
             options,
@@ -98,9 +112,12 @@ abstract class CommonGoogleGenPlugin extends GenkitPlugin {
           final systemMessage = req.messages
               .where((m) => m.role == Role.system)
               .firstOrNull;
-          final messages = req.messages
+          final nonSystemMessages = req.messages
               .where((m) => m.role != Role.system)
               .toList();
+          final messages = isGemma
+              ? stripReasoningParts(nonSystemMessages)
+              : nonSystemMessages;
 
           final generateRequest = gcl.GenerateContentRequest(
             contents: toGeminiContent(messages),
@@ -189,6 +206,15 @@ abstract class CommonGoogleGenPlugin extends GenkitPlugin {
       return createEmbedder(name);
     }
     if (actionType == 'model') {
+      if (isGemmaModelName(name)) {
+        return createModel(
+          name,
+          GemmaOptions.$schema,
+          modelInfo: isGemma3ModelName(name)
+              ? gemma3ModelInfo
+              : commonGemmaModelInfo,
+        );
+      }
       if (name.contains('-tts')) {
         return createModel(name, GeminiTtsOptions.$schema);
       }

packages/genkit_google_genai/lib/src/gemma.dart

@@ -0,0 +1,88 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import 'package:genkit/plugin.dart';
+
+import 'model.dart';
+
+final commonGemmaModelInfo = ModelInfo(
+  supports: {
+    'multiturn': true,
+    'media': true,
+    'tools': true,
+    'toolChoice': true,
+    'systemRole': true,
+    'constrained': 'no-tools',
+  },
+);
+
+final gemma3ModelInfo = ModelInfo(
+  supports: {...?commonGemmaModelInfo.supports, 'systemRole': false},
+);
+
+bool isGemmaModelName(String name) => name.startsWith('gemma-');
+
+bool isGemma3ModelName(String name) =>
+    name.startsWith('gemma-3-') || name.startsWith('gemma-3n-');
+
+/// Strips parts that the Gemma API rejects in history: reasoning parts
+/// and any text/tool parts whose metadata carries a `thoughtSignature`.
+/// Messages that become empty after filtering are dropped.
+List<Message> stripReasoningParts(List<Message> messages) {
+  return messages
+      .map(
+        (m) => Message(
+          role: m.role,
+          content: m.content
+              .where(
+                (p) =>
+                    !p.isReasoning && p.metadata?['thoughtSignature'] == null,
+              )
+              .toList(),
+          metadata: m.metadata,
+        ),
+      )
+      .where((m) => m.content.isNotEmpty)
+      .toList();
+}
+
+/// Maps a [GemmaOptions] config to its [GeminiOptions] equivalent so the
+/// shared `toGeminiSettings`/`toGeminiTools`/etc. helpers can be reused.
+/// Every Gemma field has an identical Gemini twin; the only schema-level
+/// difference is the tighter `temperature` cap on Gemma.
+GeminiOptions gemmaToGeminiOptions(GemmaOptions o) {
+  return GeminiOptions(
+    apiKey: o.apiKey,
+    safetySettings: o.safetySettings,
+    codeExecution: o.codeExecution,
+    functionCallingConfig: o.functionCallingConfig,
+    thinkingConfig: o.thinkingConfig,
+    responseModalities: o.responseModalities,
+    googleSearch: o.googleSearch,
+    fileSearch: o.fileSearch,
+    temperature: o.temperature,
+    topP: o.topP,
+    topK: o.topK,
+    candidateCount: o.candidateCount,
+    stopSequences: o.stopSequences,
+    maxOutputTokens: o.maxOutputTokens,
+    responseMimeType: o.responseMimeType,
+    responseLogprobs: o.responseLogprobs,
+    logprobs: o.logprobs,
+    presencePenalty: o.presencePenalty,
+    frequencyPenalty: o.frequencyPenalty,
+    seed: o.seed,
+    speechConfig: o.speechConfig,
+  );
+}

packages/genkit_google_genai/lib/src/google_api_client.dart

@@ -17,6 +17,7 @@ import 'package:meta/meta.dart';
 
 import 'api_client.dart';
 import 'common_plugin.dart';
+import 'gemma.dart';
 import 'generated/generativelanguage.dart' as gcl;
 import 'model.dart';
 
@@ -54,12 +55,23 @@ class GoogleGenAiPluginImpl extends CommonGoogleGenPlugin {
       final models = (modelsResponse.models ?? [])
           .where((model) {
             return model.name != null &&
-                model.name!.startsWith('models/gemini-');
+                (model.name!.startsWith('models/gemini-') ||
+                    model.name!.startsWith('models/gemma-'));
           })
           .map((model) {
-            final isTts = model.name!.contains('-tts');
+            final short = model.name!.split('/').last;
+            if (isGemmaModelName(short)) {
+              return modelMetadata(
+                '$name/$short',
+                customOptions: GemmaOptions.$schema,
+                modelInfo: isGemma3ModelName(short)
+                    ? gemma3ModelInfo
+                    : commonGemmaModelInfo,
+              );
+            }
+            final isTts = short.contains('-tts');
             return modelMetadata(
-              '$name/${model.name!.split('/').last}',
+              '$name/$short',
               customOptions: isTts
                   ? GeminiTtsOptions.$schema
                   : GeminiOptions.$schema,

packages/genkit_google_genai/lib/src/model.dart

@@ -56,6 +56,42 @@ abstract class $GeminiOptions {
   $SpeechConfig? get speechConfig;
 }
 
+@Schema()
+abstract class $GemmaOptions {
+  String? get apiKey;
+
+  List<$SafetySettings>? get safetySettings;
+
+  bool? get codeExecution;
+  $FunctionCallingConfig? get functionCallingConfig;
+  $ThinkingConfig? get thinkingConfig;
+  List<String>? get responseModalities;
+
+  // Retrieval
+  $GoogleSearch? get googleSearch;
+  $FileSearch? get fileSearch;
+
+  @DoubleField(minimum: 0.0, maximum: 1.0)
+  double? get temperature;
+
+  @DoubleField(minimum: 0.0, maximum: 1.0)
+  double? get topP;
+
+  int? get topK;
+  int? get candidateCount;
+  List<String>? get stopSequences;
+  int? get maxOutputTokens;
+
+  String? get responseMimeType;
+  bool? get responseLogprobs;
+  int? get logprobs;
+  double? get presencePenalty;
+  double? get frequencyPenalty;
+  int? get seed;
+
+  $SpeechConfig? get speechConfig;
+}
+
 @Schema()
 abstract class $SafetySettings {
   @StringField(