Feat: Implement Gemini Interaction API in adk-js

core/package.json

@@ -45,7 +45,7 @@
     "@google-cloud/opentelemetry-cloud-trace-exporter": "^3.0.0",
     "@google-cloud/storage": "^7.17.1",
     "@google-cloud/vertexai": "^1.12.0",
-    "@google/genai": "^1.37.0",
+    "@google/genai": "^2.0.0",
     "@mikro-orm/core": "^6.6.10",
     "@mikro-orm/reflection": "^6.6.6",
     "@modelcontextprotocol/sdk": "^1.26.0",

core/src/agents/llm_agent.ts

@@ -62,6 +62,7 @@ import {CONTENT_REQUEST_PROCESSOR} from './processors/content_request_processor.
 import {ContextCompactorRequestProcessor} from './processors/context_compactor_request_processor.js';
 import {IDENTITY_LLM_REQUEST_PROCESSOR} from './processors/identity_llm_request_processor.js';
 import {INSTRUCTIONS_LLM_REQUEST_PROCESSOR} from './processors/instructions_llm_request_processor.js';
+import {INTERACTIONS_REQUEST_PROCESSOR} from './processors/interactions_request_processor.js';
 import {REQUEST_CONFIRMATION_LLM_REQUEST_PROCESSOR} from './processors/request_confirmation_llm_request_processor.js';
 import {TOOL_FILTER_REQUEST_PROCESSOR} from './processors/tool_filter_request_processor.js';
 import {ReadonlyContext} from './readonly_context.js';
@@ -396,6 +397,7 @@ export class LlmAgent extends BaseAgent {
       INSTRUCTIONS_LLM_REQUEST_PROCESSOR,
       REQUEST_CONFIRMATION_LLM_REQUEST_PROCESSOR,
       CONTENT_REQUEST_PROCESSOR,
+      INTERACTIONS_REQUEST_PROCESSOR,
       CODE_EXECUTION_REQUEST_PROCESSOR,
       TOOL_FILTER_REQUEST_PROCESSOR,
     ];

core/src/agents/processors/interactions_request_processor.ts

@@ -0,0 +1,49 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {Event} from '../../events/event.js';
+import {Gemini} from '../../models/google_llm.js';
+import {LlmRequest} from '../../models/llm_request.js';
+import {InvocationContext} from '../invocation_context.js';
+import {isLlmAgent} from '../llm_agent.js';
+import {BaseLlmRequestProcessor} from './base_llm_processor.js';
+
+/**
+ * Request processor for Gemini Interactions API.
+ * Resolves the previous interaction ID from the session history.
+ */
+export class InteractionsRequestProcessor implements BaseLlmRequestProcessor {
+  // eslint-disable-next-line require-yield
+  async *runAsync(
+    invocationContext: InvocationContext,
+    llmRequest: LlmRequest,
+  ): AsyncGenerator<Event, void, void> {
+    const agent = invocationContext.agent;
+    if (!agent || !isLlmAgent(agent)) {
+      return;
+    }
+
+    const model = agent.canonicalModel;
+    if (model instanceof Gemini && model.useInteractionsApi) {
+      const events = invocationContext.session.events;
+      for (let i = events.length - 1; i >= 0; i--) {
+        const event = events[i];
+        // Skip events not belonging to the current branch or author
+        if (
+          event.branch === invocationContext.branch &&
+          event.author === agent.name &&
+          event.interactionId
+        ) {
+          llmRequest.previousInteractionId = event.interactionId;
+          break;
+        }
+      }
+    }
+  }
+}
+
+export const INTERACTIONS_REQUEST_PROCESSOR =
+  new InteractionsRequestProcessor();

core/src/common.ts

@@ -47,6 +47,10 @@ export {
   ContentRequestProcessor,
 } from './agents/processors/content_request_processor.js';
 export {ContextCompactorRequestProcessor} from './agents/processors/context_compactor_request_processor.js';
+export {
+  INTERACTIONS_REQUEST_PROCESSOR,
+  InteractionsRequestProcessor,
+} from './agents/processors/interactions_request_processor.js';
 export {ReadonlyContext} from './agents/readonly_context.js';
 export {RoutedAgent, isRoutedAgent} from './agents/routed_agent.js';
 export type {AgentRouter, RoutedAgentConfig} from './agents/routed_agent.js';

core/src/models/google_llm.ts

@@ -20,6 +20,7 @@ import {StreamingResponseAggregator} from '../utils/streaming_utils.js';
 import {BaseLlm} from './base_llm.js';
 import {BaseLlmConnection} from './base_llm_connection.js';
 import {GeminiLlmConnection} from './gemini_llm_connection.js';
+import {generateContentViaInteractions} from './interactions_utils.js';
 import {LlmRequest} from './llm_request.js';
 import {createLlmResponse, LlmResponse} from './llm_response.js';
 
@@ -53,6 +54,10 @@ export interface GeminiParams {
    * Headers to merge with internally crafted headers.
    */
   headers?: Record<string, string>;
+  /**
+   * Whether to use the Interactions API for stateful conversations.
+   */
+  useInteractionsApi?: boolean;
 }
 
 /**
@@ -64,6 +69,7 @@ export class Gemini extends BaseLlm {
   private readonly project?: string;
   private readonly location?: string;
   private readonly headers?: Record<string, string>;
+  readonly useInteractionsApi: boolean;
 
   /**
    * @param params The parameters for creating a Gemini instance.
@@ -75,6 +81,7 @@ export class Gemini extends BaseLlm {
     project,
     location,
     headers,
+    useInteractionsApi,
   }: GeminiParams) {
     if (!model) {
       model = 'gemini-2.5-flash';
@@ -99,6 +106,7 @@ export class Gemini extends BaseLlm {
     this.apiKey = params.apiKey;
     this.headers = headers;
     this.vertexai = !!params.vertexai;
+    this.useInteractionsApi = !!useInteractionsApi;
   }
 
   /**
@@ -132,6 +140,10 @@ export class Gemini extends BaseLlm {
     stream = false,
     abortSignal?: AbortSignal,
   ): AsyncGenerator<LlmResponse, void> {
+    if (this.useInteractionsApi) {
+      yield* generateContentViaInteractions(this.apiClient, llmRequest, stream);
+      return;
+    }
     this.preprocessRequest(llmRequest);
     this.maybeAppendUserContent(llmRequest);
     logger.info(