Clearcut logging - initial implementation (#1274)

Flag-guarded initial implementation of a clearcut logger to collect telemetry data and send it to Concord for dashboards, etc.

16 files changed, 1028 insertions, 319 deletions

diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index be21ac8c..f6128e11 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -33,8 +33,10 @@ import {
   DEFAULT_TELEMETRY_TARGET,
   DEFAULT_OTLP_ENDPOINT,
   TelemetryTarget,
+  StartSessionEvent,
 } from '../telemetry/index.js';
 import { DEFAULT_GEMINI_EMBEDDING_MODEL } from './models.js';
+import { ClearcutLogger } from '../telemetry/clearcut-logger/clearcut-logger.js';
 
 export enum ApprovalMode {
   DEFAULT = 'default',
@@ -55,6 +57,7 @@ export interface TelemetrySettings {
   target?: TelemetryTarget;
   otlpEndpoint?: string;
   logPrompts?: boolean;
+  disableDataCollection?: boolean;
 }
 
 export class MCPServerConfig {
@@ -114,6 +117,7 @@ export interface ConfigParameters {
   fileDiscoveryService?: FileDiscoveryService;
   bugCommand?: BugCommandSettings;
   model: string;
+  disableDataCollection?: boolean;
 }
 
 export class Config {
@@ -150,6 +154,7 @@ export class Config {
   private readonly cwd: string;
   private readonly bugCommand: BugCommandSettings | undefined;
   private readonly model: string;
+  private readonly disableDataCollection: boolean;
 
   constructor(params: ConfigParameters) {
     this.sessionId = params.sessionId;
@@ -189,6 +194,8 @@ export class Config {
     this.fileDiscoveryService = params.fileDiscoveryService ?? null;
     this.bugCommand = params.bugCommand;
     this.model = params.model;
+    this.disableDataCollection =
+      params.telemetry?.disableDataCollection ?? true;
 
     if (params.contextFileName) {
       setGeminiMdFilename(params.contextFileName);
@@ -197,6 +204,12 @@ export class Config {
     if (this.telemetrySettings.enabled) {
       initializeTelemetry(this);
     }
+
+    if (!this.disableDataCollection) {
+      ClearcutLogger.getInstance(this)?.enqueueLogEvent(
+        new StartSessionEvent(this),
+      );
+    }
   }
 
   async refreshAuth(authMethod: AuthType) {
@@ -370,6 +383,10 @@ export class Config {
     return this.fileDiscoveryService;
   }
 
+  getDisableDataCollection(): boolean {
+    return this.disableDataCollection;
+  }
+
   async getGitService(): Promise<GitService> {
     if (!this.gitService) {
       this.gitService = new GitService(this.targetDir);
diff --git a/packages/core/src/core/coreToolScheduler.test.ts b/packages/core/src/core/coreToolScheduler.test.ts
index 63feb874..656f8952 100644
--- a/packages/core/src/core/coreToolScheduler.test.ts
+++ b/packages/core/src/core/coreToolScheduler.test.ts
@@ -77,6 +77,7 @@ describe('CoreToolScheduler', () => {
 
     const mockConfig = {
       getSessionId: () => 'test-session-id',
+      getDisableDataCollection: () => false,
     } as Config;
 
     const scheduler = new CoreToolScheduler({
diff --git a/packages/core/src/core/coreToolScheduler.ts b/packages/core/src/core/coreToolScheduler.ts
index 14a39792..5e41f0c5 100644
--- a/packages/core/src/core/coreToolScheduler.ts
+++ b/packages/core/src/core/coreToolScheduler.ts
@@ -16,6 +16,7 @@ import {
   EditorType,
   Config,
   logToolCall,
+  ToolCallEvent,
 } from '../index.js';
 import { Part, PartListUnion } from '@google/genai';
 import { getResponseTextFromParts } from '../utils/generateContentResponseUtilities.js';
@@ -652,20 +653,7 @@ export class CoreToolScheduler {
       this.toolCalls = [];
 
       for (const call of completedCalls) {
-        logToolCall(
-          this.config,
-          {
-            function_name: call.request.name,
-            function_args: call.request.args,
-            duration_ms: call.durationMs ?? 0,
-            success: call.status === 'success',
-            error:
-              call.status === 'error'
-                ? call.response.error?.message
-                : undefined,
-          },
-          call.outcome,
-        );
+        logToolCall(this.config, new ToolCallEvent(call));
       }
 
       if (this.onAllToolCallsComplete) {
diff --git a/packages/core/src/core/geminiChat.test.ts b/packages/core/src/core/geminiChat.test.ts
index 9961103d..45c9b06e 100644
--- a/packages/core/src/core/geminiChat.test.ts
+++ b/packages/core/src/core/geminiChat.test.ts
@@ -27,6 +27,7 @@ const mockModelsModule = {
 const mockConfig = {
   getSessionId: () => 'test-session-id',
   getTelemetryLogPromptsEnabled: () => true,
+  getDisableDataCollection: () => false,
 } as unknown as Config;
 
 describe('GeminiChat', () => {
diff --git a/packages/core/src/core/geminiChat.ts b/packages/core/src/core/geminiChat.ts
index 3929dd26..e08aaf86 100644
--- a/packages/core/src/core/geminiChat.ts
+++ b/packages/core/src/core/geminiChat.ts
@@ -24,12 +24,16 @@ import {
   logApiRequest,
   logApiResponse,
   logApiError,
-  getFinalUsageMetadata,
 } from '../telemetry/loggers.js';
 import {
   getStructuredResponse,
   getStructuredResponseFromParts,
 } from '../utils/generateContentResponseUtilities.js';
+import {
+  ApiErrorEvent,
+  ApiRequestEvent,
+  ApiResponseEvent,
+} from '../telemetry/types.js';
 
 /**
  * Returns true if the response is valid, false otherwise.
@@ -152,14 +156,8 @@ export class GeminiChat {
     contents: Content[],
     model: string,
   ): Promise<void> {
-    const shouldLogUserPrompts = (config: Config): boolean =>
-      config.getTelemetryLogPromptsEnabled() ?? false;
-
     const requestText = this._getRequestTextFromContents(contents);
-    logApiRequest(this.config, {
-      model,
-      request_text: shouldLogUserPrompts(this.config) ? requestText : undefined,
-    });
+    logApiRequest(this.config, new ApiRequestEvent(model, requestText));
   }
 
   private async _logApiResponse(
@@ -167,31 +165,20 @@ export class GeminiChat {
     usageMetadata?: GenerateContentResponseUsageMetadata,
     responseText?: string,
   ): Promise<void> {
-    logApiResponse(this.config, {
-      model: this.model,
-      duration_ms: durationMs,
-      status_code: 200, // Assuming 200 for success
-      input_token_count: usageMetadata?.promptTokenCount ?? 0,
-      output_token_count: usageMetadata?.candidatesTokenCount ?? 0,
-      cached_content_token_count: usageMetadata?.cachedContentTokenCount ?? 0,
-      thoughts_token_count: usageMetadata?.thoughtsTokenCount ?? 0,
-      tool_token_count: usageMetadata?.toolUsePromptTokenCount ?? 0,
-      response_text: responseText,
-    });
+    logApiResponse(
+      this.config,
+      new ApiResponseEvent(this.model, durationMs, usageMetadata, responseText),
+    );
   }
 
   private _logApiError(durationMs: number, error: unknown): void {
     const errorMessage = error instanceof Error ? error.message : String(error);
     const errorType = error instanceof Error ? error.name : 'unknown';
-    const statusCode = 'unknown';
 
-    logApiError(this.config, {
-      model: this.model,
-      error: errorMessage,
-      status_code: statusCode,
-      error_type: errorType,
-      duration_ms: durationMs,
-    });
+    logApiError(
+      this.config,
+      new ApiErrorEvent(this.model, errorMessage, durationMs, errorType),
+    );
   }
 
   /**
@@ -402,6 +389,17 @@ export class GeminiChat {
     this.history = history;
   }
 
+  getFinalUsageMetadata(
+    chunks: GenerateContentResponse[],
+  ): GenerateContentResponseUsageMetadata | undefined {
+    const lastChunkWithMetadata = chunks
+      .slice()
+      .reverse()
+      .find((chunk) => chunk.usageMetadata);
+
+    return lastChunkWithMetadata?.usageMetadata;
+  }
+
   private async *processStreamResponse(
     streamResponse: AsyncGenerator<GenerateContentResponse>,
     inputContent: Content,
@@ -444,7 +442,7 @@ export class GeminiChat {
       const fullText = getStructuredResponseFromParts(allParts);
       await this._logApiResponse(
         durationMs,
-        getFinalUsageMetadata(chunks),
+        this.getFinalUsageMetadata(chunks),
         fullText,
       );
     }
diff --git a/packages/core/src/core/nonInteractiveToolExecutor.test.ts b/packages/core/src/core/nonInteractiveToolExecutor.test.ts
index edf11d35..c6874c6e 100644
--- a/packages/core/src/core/nonInteractiveToolExecutor.test.ts
+++ b/packages/core/src/core/nonInteractiveToolExecutor.test.ts
@@ -16,7 +16,10 @@ import {
 } from '../index.js';
 import { Part, Type } from '@google/genai';
 
-const mockConfig = {} as unknown as Config;
+const mockConfig = {
+  getSessionId: () => 'test-session-id',
+  getDisableDataCollection: () => false,
+} as unknown as Config;
 
 describe('executeToolCall', () => {
   let mockToolRegistry: ToolRegistry;
diff --git a/packages/core/src/core/nonInteractiveToolExecutor.ts b/packages/core/src/core/nonInteractiveToolExecutor.ts
index f2174e06..8efb58e0 100644
--- a/packages/core/src/core/nonInteractiveToolExecutor.ts
+++ b/packages/core/src/core/nonInteractiveToolExecutor.ts
@@ -33,6 +33,8 @@ export async function executeToolCall(
     );
     const durationMs = Date.now() - startTime;
     logToolCall(config, {
+      'event.name': 'tool_call',
+      'event.timestamp': new Date().toISOString(),
       function_name: toolCallRequest.name,
       function_args: toolCallRequest.args,
       duration_ms: durationMs,
@@ -67,6 +69,8 @@ export async function executeToolCall(
 
     const durationMs = Date.now() - startTime;
     logToolCall(config, {
+      'event.name': 'tool_call',
+      'event.timestamp': new Date().toISOString(),
       function_name: toolCallRequest.name,
       function_args: toolCallRequest.args,
       duration_ms: durationMs,
@@ -89,6 +93,8 @@ export async function executeToolCall(
     const error = e instanceof Error ? e : new Error(String(e));
     const durationMs = Date.now() - startTime;
     logToolCall(config, {
+      'event.name': 'tool_call',
+      'event.timestamp': new Date().toISOString(),
       function_name: toolCallRequest.name,
       function_args: toolCallRequest.args,
       duration_ms: durationMs,
diff --git a/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
new file mode 100644
index 00000000..8da928c7
--- /dev/null
+++ b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
@@ -0,0 +1,338 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { Buffer } from 'buffer';
+import * as https from 'https';
+import {
+  StartSessionEvent,
+  EndSessionEvent,
+  UserPromptEvent,
+  ToolCallEvent,
+  ApiRequestEvent,
+  ApiResponseEvent,
+  ApiErrorEvent,
+} from '../types.js';
+import { EventMetadataKey } from './event-metadata-key.js';
+import { Config } from '../../config/config.js';
+import { getPersistentUserId } from '../../utils/user_id.js';
+
+const start_session_event_name = 'start_session';
+const new_prompt_event_name = 'new_prompt';
+const tool_call_event_name = 'tool_call';
+const api_request_event_name = 'api_request';
+const api_response_event_name = 'api_response';
+const api_error_event_name = 'api_error';
+const end_session_event_name = 'end_session';
+
+export interface LogResponse {
+  nextRequestWaitMs?: number;
+}
+
+// Singleton class for batch posting log events to Clearcut. When a new event comes in, the elapsed time
+// is checked and events are flushed to Clearcut if at least a minute has passed since the last flush.
+export class ClearcutLogger {
+  private static instance: ClearcutLogger;
+  private config?: Config;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any -- Clearcut expects this format.
+  private readonly events: any = [];
+  private last_flush_time: number = Date.now();
+  private flush_interval_ms: number = 1000 * 60; // Wait at least a minute before flushing events.
+
+  private constructor(config?: Config) {
+    this.config = config;
+  }
+
+  static getInstance(config?: Config): ClearcutLogger | undefined {
+    if (config === undefined || config?.getDisableDataCollection())
+      return undefined;
+    if (!ClearcutLogger.instance) {
+      ClearcutLogger.instance = new ClearcutLogger(config);
+    }
+    return ClearcutLogger.instance;
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any -- Clearcut expects this format.
+  enqueueLogEvent(event: any): void {
+    this.events.push([
+      {
+        event_time_ms: Date.now(),
+        source_extension_json: JSON.stringify(event),
+      },
+    ]);
+  }
+
+  createLogEvent(name: string, data: Map<EventMetadataKey, string>): object {
+    return {
+      Application: 'GEMINI_CLI',
+      event_name: name,
+      client_install_id: getPersistentUserId(),
+      event_metadata: [data] as object[],
+    };
+  }
+
+  flushIfNeeded(): void {
+    if (Date.now() - this.last_flush_time < this.flush_interval_ms) {
+      return;
+    }
+
+    this.flushToClearcut();
+    this.last_flush_time = Date.now();
+  }
+
+  flushToClearcut(): Promise<LogResponse> {
+    return new Promise<Buffer>((resolve, reject) => {
+      const request = [
+        {
+          log_source_name: 'CONCORD',
+          request_time_ms: Date.now(),
+          log_event: this.events,
+        },
+      ];
+      const body = JSON.stringify(request);
+      const options = {
+        hostname: 'play.googleapis.com',
+        path: '/log',
+        method: 'POST',
+        headers: { 'Content-Length': Buffer.byteLength(body) },
+      };
+      const bufs: Buffer[] = [];
+      const req = https.request(options, (res) => {
+        res.on('data', (buf) => bufs.push(buf));
+        res.on('end', () => {
+          resolve(Buffer.concat(bufs));
+        });
+      });
+      req.on('error', (e) => {
+        reject(e);
+      });
+      req.end(body);
+    }).then((buf: Buffer) => {
+      try {
+        this.events.length = 0;
+        return this.decodeLogResponse(buf) || {};
+      } catch (error: unknown) {
+        console.error('Error flushing log events:', error);
+        return {};
+      }
+    });
+  }
+
+  // Visible for testing. Decodes protobuf-encoded response from Clearcut server.
+  decodeLogResponse(buf: Buffer): LogResponse | undefined {
+    // TODO(obrienowen): return specific errors to facilitate debugging.
+    if (buf.length < 1) {
+      return undefined;
+    }
+
+    // The first byte of the buffer is `field<<3 | type`. We're looking for field
+    // 1, with type varint, represented by type=0. If the first byte isn't 8, that
+    // means field 1 is missing or the message is corrupted. Either way, we return
+    // undefined.
+    if (buf.readUInt8(0) !== 8) {
+      return undefined;
+    }
+
+    let ms = BigInt(0);
+    let cont = true;
+
+    // In each byte, the most significant bit is the continuation bit. If it's
+    // set, we keep going. The lowest 7 bits, are data bits. They are concatenated
+    // in reverse order to form the final number.
+    for (let i = 1; cont && i < buf.length; i++) {
+      const byte = buf.readUInt8(i);
+      ms |= BigInt(byte & 0x7f) << BigInt(7 * (i - 1));
+      cont = (byte & 0x80) !== 0;
+    }
+
+    if (cont) {
+      // We have fallen off the buffer without seeing a terminating byte. The
+      // message is corrupted.
+      return undefined;
+    }
+    return {
+      nextRequestWaitMs: Number(ms),
+    };
+  }
+
+  logStartSessionEvent(event: StartSessionEvent): void {
+    const data: Map<EventMetadataKey, string> = new Map();
+
+    data.set(EventMetadataKey.GEMINI_CLI_START_SESSION_MODEL, event.model);
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_EMBEDDING_MODEL,
+      event.embedding_model,
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_SANDBOX,
+      event.sandbox_enabled.toString(),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_CORE_TOOLS,
+      event.core_tools_enabled,
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_APPROVAL_MODE,
+      event.approval_mode,
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_API_KEY_ENABLED,
+      event.api_key_enabled.toString(),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_VERTEX_API_ENABLED,
+      event.vertex_ai_enabled.toString(),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_DEBUG_MODE_ENABLED,
+      event.debug_enabled.toString(),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_MCP_SERVERS,
+      event.mcp_servers,
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_TELEMETRY_ENABLED,
+      event.telemetry_enabled.toString(),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_START_SESSION_TELEMETRY_LOG_USER_PROMPTS_ENABLED,
+      event.telemetry_log_user_prompts_enabled.toString(),
+    );
+
+    this.enqueueLogEvent(this.createLogEvent(start_session_event_name, data));
+    this.flushIfNeeded();
+  }
+
+  logNewPromptEvent(event: UserPromptEvent): void {
+    const data: Map<EventMetadataKey, string> = new Map();
+
+    data.set(
+      EventMetadataKey.GEMINI_CLI_USER_PROMPT_LENGTH,
+      JSON.stringify(event.prompt_length),
+    );
+
+    this.enqueueLogEvent(this.createLogEvent(new_prompt_event_name, data));
+    this.flushIfNeeded();
+  }
+
+  logToolCallEvent(event: ToolCallEvent): void {
+    const data: Map<EventMetadataKey, string> = new Map();
+
+    data.set(EventMetadataKey.GEMINI_CLI_TOOL_CALL_NAME, event.function_name);
+    data.set(
+      EventMetadataKey.GEMINI_CLI_TOOL_CALL_DECISION,
+      JSON.stringify(event.decision),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_TOOL_CALL_SUCCESS,
+      JSON.stringify(event.success),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_TOOL_CALL_DURATION_MS,
+      JSON.stringify(event.duration_ms),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_TOOL_ERROR_MESSAGE,
+      JSON.stringify(event.error),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_TOOL_CALL_ERROR_TYPE,
+      JSON.stringify(event.error_type),
+    );
+
+    this.enqueueLogEvent(this.createLogEvent(tool_call_event_name, data));
+    this.flushIfNeeded();
+  }
+
+  logApiRequestEvent(event: ApiRequestEvent): void {
+    const data: Map<EventMetadataKey, string> = new Map();
+
+    data.set(EventMetadataKey.GEMINI_CLI_API_REQUEST_MODEL, event.model);
+
+    this.enqueueLogEvent(this.createLogEvent(api_request_event_name, data));
+    this.flushIfNeeded();
+  }
+
+  logApiResponseEvent(event: ApiResponseEvent): void {
+    const data: Map<EventMetadataKey, string> = new Map();
+
+    data.set(EventMetadataKey.GEMINI_CLI_API_RESPONSE_MODEL, event.model);
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_RESPONSE_STATUS_CODE,
+      JSON.stringify(event.status_code),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_RESPONSE_DURATION_MS,
+      JSON.stringify(event.duration_ms),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_ERROR_MESSAGE,
+      JSON.stringify(event.error),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_RESPONSE_INPUT_TOKEN_COUNT,
+      JSON.stringify(event.input_token_count),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_RESPONSE_OUTPUT_TOKEN_COUNT,
+      JSON.stringify(event.output_token_count),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_RESPONSE_CACHED_TOKEN_COUNT,
+      JSON.stringify(event.cached_content_token_count),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_RESPONSE_THINKING_TOKEN_COUNT,
+      JSON.stringify(event.thoughts_token_count),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_RESPONSE_TOOL_TOKEN_COUNT,
+      JSON.stringify(event.tool_token_count),
+    );
+
+    this.enqueueLogEvent(this.createLogEvent(api_response_event_name, data));
+    this.flushIfNeeded();
+  }
+
+  logApiErrorEvent(event: ApiErrorEvent): void {
+    const data: Map<EventMetadataKey, string> = new Map();
+
+    data.set(EventMetadataKey.GEMINI_CLI_API_ERROR_MODEL, event.model);
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_ERROR_TYPE,
+      JSON.stringify(event.error_type),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_ERROR_STATUS_CODE,
+      JSON.stringify(event.status_code),
+    );
+    data.set(
+      EventMetadataKey.GEMINI_CLI_API_ERROR_DURATION_MS,
+      JSON.stringify(event.duration_ms),
+    );
+
+    this.enqueueLogEvent(this.createLogEvent(api_error_event_name, data));
+    this.flushIfNeeded();
+  }
+
+  logEndSessionEvent(event: EndSessionEvent): void {
+    const data: Map<EventMetadataKey, string> = new Map();
+
+    data.set(
+      EventMetadataKey.GEMINI_CLI_END_SESSION_ID,
+      event?.session_id?.toString() ?? '',
+    );
+
+    this.enqueueLogEvent(this.createLogEvent(end_session_event_name, data));
+    // Flush immediately on session end.
+    this.flushToClearcut();
+  }
+
+  shutdown() {
+    const event = new EndSessionEvent(this.config);
+    this.logEndSessionEvent(event);
+  }
+}
diff --git a/packages/core/src/telemetry/clearcut-logger/event-metadata-key.ts b/packages/core/src/telemetry/clearcut-logger/event-metadata-key.ts
new file mode 100644
index 00000000..146dcdeb
--- /dev/null
+++ b/packages/core/src/telemetry/clearcut-logger/event-metadata-key.ts
@@ -0,0 +1,153 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// Defines valid event metadata keys for Clearcut logging.
+export enum EventMetadataKey {
+  GEMINI_CLI_KEY_UNKNOWN = 0,
+
+  // ==========================================================================
+  // Start Session Event Keys
+  // ===========================================================================
+
+  // Logs the model id used in the session.
+  GEMINI_CLI_START_SESSION_MODEL = 1,
+
+  // Logs the embedding model id used in the session.
+  GEMINI_CLI_START_SESSION_EMBEDDING_MODEL = 2,
+
+  // Logs the sandbox that was used in the session.
+  GEMINI_CLI_START_SESSION_SANDBOX = 3,
+
+  // Logs the core tools that were enabled in the session.
+  GEMINI_CLI_START_SESSION_CORE_TOOLS = 4,
+
+  // Logs the approval mode that was used in the session.
+  GEMINI_CLI_START_SESSION_APPROVAL_MODE = 5,
+
+  // Logs whether an API key was used in the session.
+  GEMINI_CLI_START_SESSION_API_KEY_ENABLED = 6,
+
+  // Logs whether the Vertex API was used in the session.
+  GEMINI_CLI_START_SESSION_VERTEX_API_ENABLED = 7,
+
+  // Logs whether debug mode was enabled in the session.
+  GEMINI_CLI_START_SESSION_DEBUG_MODE_ENABLED = 8,
+
+  // Logs the MCP servers that were enabled in the session.
+  GEMINI_CLI_START_SESSION_MCP_SERVERS = 9,
+
+  // Logs whether user-collected telemetry was enabled in the session.
+  GEMINI_CLI_START_SESSION_TELEMETRY_ENABLED = 10,
+
+  // Logs whether prompt collection was enabled for user-collected telemetry.
+  GEMINI_CLI_START_SESSION_TELEMETRY_LOG_USER_PROMPTS_ENABLED = 11,
+
+  // Logs whether the session was configured to respect gitignore files.
+  GEMINI_CLI_START_SESSION_RESPECT_GITIGNORE = 12,
+
+  // ==========================================================================
+  // User Prompt Event Keys
+  // ===========================================================================
+
+  // Logs the length of the prompt.
+  GEMINI_CLI_USER_PROMPT_LENGTH = 13,
+
+  // ==========================================================================
+  // Tool Call Event Keys
+  // ===========================================================================
+
+  // Logs the function name.
+  GEMINI_CLI_TOOL_CALL_NAME = 14,
+
+  // Logs the user's decision about how to handle the tool call.
+  GEMINI_CLI_TOOL_CALL_DECISION = 15,
+
+  // Logs whether the tool call succeeded.
+  GEMINI_CLI_TOOL_CALL_SUCCESS = 16,
+
+  // Logs the tool call duration in milliseconds.
+  GEMINI_CLI_TOOL_CALL_DURATION_MS = 17,
+
+  // Logs the tool call error message, if any.
+  GEMINI_CLI_TOOL_ERROR_MESSAGE = 18,
+
+  // Logs the tool call error type, if any.
+  GEMINI_CLI_TOOL_CALL_ERROR_TYPE = 19,
+
+  // ==========================================================================
+  // GenAI API Request Event Keys
+  // ===========================================================================
+
+  // Logs the model id of the request.
+  GEMINI_CLI_API_REQUEST_MODEL = 20,
+
+  // ==========================================================================
+  // GenAI API Response Event Keys
+  // ===========================================================================
+
+  // Logs the model id of the API call.
+  GEMINI_CLI_API_RESPONSE_MODEL = 21,
+
+  // Logs the status code of the response.
+  GEMINI_CLI_API_RESPONSE_STATUS_CODE = 22,
+
+  // Logs the duration of the API call in milliseconds.
+  GEMINI_CLI_API_RESPONSE_DURATION_MS = 23,
+
+  // Logs the error message of the API call, if any.
+  GEMINI_CLI_API_ERROR_MESSAGE = 24,
+
+  // Logs the input token count of the API call.
+  GEMINI_CLI_API_RESPONSE_INPUT_TOKEN_COUNT = 25,
+
+  // Logs the output token count of the API call.
+  GEMINI_CLI_API_RESPONSE_OUTPUT_TOKEN_COUNT = 26,
+
+  // Logs the cached token count of the API call.
+  GEMINI_CLI_API_RESPONSE_CACHED_TOKEN_COUNT = 27,
+
+  // Logs the thinking token count of the API call.
+  GEMINI_CLI_API_RESPONSE_THINKING_TOKEN_COUNT = 28,
+
+  // Logs the tool use token count of the API call.
+  GEMINI_CLI_API_RESPONSE_TOOL_TOKEN_COUNT = 29,
+
+  // ==========================================================================
+  // GenAI API Error Event Keys
+  // ===========================================================================
+
+  // Logs the model id of the API call.
+  GEMINI_CLI_API_ERROR_MODEL = 30,
+
+  // Logs the error type.
+  GEMINI_CLI_API_ERROR_TYPE = 31,
+
+  // Logs the status code of the error response.
+  GEMINI_CLI_API_ERROR_STATUS_CODE = 32,
+
+  // Logs the duration of the API call in milliseconds.
+  GEMINI_CLI_API_ERROR_DURATION_MS = 33,
+
+  // ==========================================================================
+  // End Session Event Keys
+  // ===========================================================================
+
+  // Logs the end of a session.
+  GEMINI_CLI_END_SESSION_ID = 34,
+}
+
+export function getEventMetadataKey(
+  keyName: string,
+): EventMetadataKey | undefined {
+  // Access the enum member by its string name
+  const key = EventMetadataKey[keyName as keyof typeof EventMetadataKey];
+
+  // Check if the result is a valid enum member (not undefined and is a number)
+  if (typeof key === 'number') {
+    return key;
+  }
+  return undefined;
+}
diff --git a/packages/core/src/telemetry/index.ts b/packages/core/src/telemetry/index.ts
index 6329b401..138c8486 100644
--- a/packages/core/src/telemetry/index.ts
+++ b/packages/core/src/telemetry/index.ts
@@ -25,15 +25,15 @@ export {
   logApiRequest,
   logApiError,
   logApiResponse,
-  getFinalUsageMetadata,
 } from './loggers.js';
 export {
+  StartSessionEvent,
+  EndSessionEvent,
   UserPromptEvent,
   ToolCallEvent,
   ApiRequestEvent,
   ApiErrorEvent,
   ApiResponseEvent,
-  CliConfigEvent,
   TelemetryEvent,
 } from './types.js';
 export { SpanStatusCode, ValueType } from '@opentelemetry/api';
diff --git a/packages/core/src/telemetry/loggers.test.ts b/packages/core/src/telemetry/loggers.test.ts
index 3fa9ad1c..2659f398 100644
--- a/packages/core/src/telemetry/loggers.test.ts
+++ b/packages/core/src/telemetry/loggers.test.ts
@@ -4,14 +4,24 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { ToolConfirmationOutcome } from '../tools/tools.js';
-import { AuthType } from '../core/contentGenerator.js';
+import {
+  AuthType,
+  CompletedToolCall,
+  ContentGeneratorConfig,
+  EditTool,
+  ErroredToolCall,
+  GeminiClient,
+  ToolConfirmationOutcome,
+  ToolRegistry,
+} from '../index.js';
 import { logs } from '@opentelemetry/api-logs';
 import { SemanticAttributes } from '@opentelemetry/semantic-conventions';
 import { Config } from '../config/config.js';
 import {
   EVENT_API_REQUEST,
   EVENT_API_RESPONSE,
+  EVENT_CLI_CONFIG,
+  EVENT_TOOL_CALL,
   EVENT_USER_PROMPT,
 } from './constants.js';
 import {
@@ -20,13 +30,19 @@ import {
   logCliConfiguration,
   logUserPrompt,
   logToolCall,
-  ToolCallDecision,
-  getFinalUsageMetadata,
 } from './loggers.js';
+import {
+  ApiRequestEvent,
+  ApiResponseEvent,
+  StartSessionEvent,
+  ToolCallDecision,
+  ToolCallEvent,
+  UserPromptEvent,
+} from './types.js';
 import * as metrics from './metrics.js';
 import * as sdk from './sdk.js';
 import { vi, describe, beforeEach, it, expect } from 'vitest';
-import { GenerateContentResponse } from '@google/genai';
+import { GenerateContentResponseUsageMetadata } from '@google/genai';
 
 describe('loggers', () => {
   const mockLogger = {
@@ -54,8 +70,11 @@ describe('loggers', () => {
           apiKey: 'test-api-key',
           authType: AuthType.USE_VERTEX_AI,
         }),
+        getTelemetryEnabled: () => true,
+        getDisableDataCollection: () => false,
         getTelemetryLogPromptsEnabled: () => true,
         getFileFilteringRespectGitIgnore: () => true,
+        getFileFilteringAllowBuildArtifacts: () => false,
         getDebugMode: () => true,
         getMcpServers: () => ({
           'test-server': {
@@ -63,15 +82,18 @@ describe('loggers', () => {
           },
         }),
         getQuestion: () => 'test-question',
+        getTargetDir: () => 'target-dir',
+        getProxy: () => 'http://test.proxy.com:8080',
       } as unknown as Config;
 
-      logCliConfiguration(mockConfig);
+      const startSessionEvent = new StartSessionEvent(mockConfig);
+      logCliConfiguration(mockConfig, startSessionEvent);
 
       expect(mockLogger.emit).toHaveBeenCalledWith({
         body: 'CLI configuration loaded.',
         attributes: {
           'session.id': 'test-session-id',
-          'event.name': 'gemini_cli.config',
+          'event.name': EVENT_CLI_CONFIG,
           'event.timestamp': '2025-01-01T00:00:00.000Z',
           model: 'test-model',
           embedding_model: 'test-embedding-model',
@@ -92,14 +114,13 @@ describe('loggers', () => {
   describe('logUserPrompt', () => {
     const mockConfig = {
       getSessionId: () => 'test-session-id',
+      getTelemetryEnabled: () => true,
       getTelemetryLogPromptsEnabled: () => true,
+      getDisableDataCollection: () => false,
     } as unknown as Config;
 
     it('should log a user prompt', () => {
-      const event = {
-        prompt: 'test-prompt',
-        prompt_length: 11,
-      };
+      const event = new UserPromptEvent(11, 'test-prompt');
 
       logUserPrompt(mockConfig, event);
 
@@ -118,12 +139,12 @@ describe('loggers', () => {
     it('should not log prompt if disabled', () => {
       const mockConfig = {
         getSessionId: () => 'test-session-id',
+        getTelemetryEnabled: () => true,
         getTelemetryLogPromptsEnabled: () => false,
+        getTargetDir: () => 'target-dir',
+        getDisableDataCollection: () => false,
       } as unknown as Config;
-      const event = {
-        prompt: 'test-prompt',
-        prompt_length: 11,
-      };
+      const event = new UserPromptEvent(11, 'test-prompt');
 
       logUserPrompt(mockConfig, event);
 
@@ -142,6 +163,10 @@ describe('loggers', () => {
   describe('logApiResponse', () => {
     const mockConfig = {
       getSessionId: () => 'test-session-id',
+      getTargetDir: () => 'target-dir',
+      getDisableDataCollection: () => false,
+      getTelemetryEnabled: () => true,
+      getTelemetryLogPromptsEnabled: () => true,
     } as Config;
 
     const mockMetrics = {
@@ -159,17 +184,19 @@ describe('loggers', () => {
     });
 
     it('should log an API response with all fields', () => {
-      const event = {
-        model: 'test-model',
-        status_code: 200,
-        duration_ms: 100,
-        input_token_count: 17,
-        output_token_count: 50,
-        cached_content_token_count: 10,
-        thoughts_token_count: 5,
-        tool_token_count: 2,
-        response_text: 'test-response',
+      const usageData: GenerateContentResponseUsageMetadata = {
+        promptTokenCount: 17,
+        candidatesTokenCount: 50,
+        cachedContentTokenCount: 10,
+        thoughtsTokenCount: 5,
+        toolUsePromptTokenCount: 2,
       };
+      const event = new ApiResponseEvent(
+        'test-model',
+        100,
+        usageData,
+        'test-response',
+      );
 
       logApiResponse(mockConfig, event);
 
@@ -209,22 +236,25 @@ describe('loggers', () => {
     });
 
     it('should log an API response with an error', () => {
-      const event = {
-        model: 'test-model',
-        duration_ms: 100,
-        error: 'test-error',
-        input_token_count: 17,
-        output_token_count: 50,
-        cached_content_token_count: 10,
-        thoughts_token_count: 5,
-        tool_token_count: 2,
-        response_text: 'test-response',
+      const usageData: GenerateContentResponseUsageMetadata = {
+        promptTokenCount: 17,
+        candidatesTokenCount: 50,
+        cachedContentTokenCount: 10,
+        thoughtsTokenCount: 5,
+        toolUsePromptTokenCount: 2,
       };
+      const event = new ApiResponseEvent(
+        'test-model',
+        100,
+        usageData,
+        'test-response',
+        'test-error',
+      );
 
       logApiResponse(mockConfig, event);
 
       expect(mockLogger.emit).toHaveBeenCalledWith({
-        body: 'API response from test-model. Status: N/A. Duration: 100ms.',
+        body: 'API response from test-model. Status: 200. Duration: 100ms.',
         attributes: {
           'session.id': 'test-session-id',
           ...event,
@@ -239,13 +269,14 @@ describe('loggers', () => {
   describe('logApiRequest', () => {
     const mockConfig = {
       getSessionId: () => 'test-session-id',
+      getTargetDir: () => 'target-dir',
+      getDisableDataCollection: () => false,
+      getTelemetryEnabled: () => true,
+      getTelemetryLogPromptsEnabled: () => true,
     } as Config;
 
     it('should log an API request with request_text', () => {
-      const event = {
-        model: 'test-model',
-        request_text: 'This is a test request',
-      };
+      const event = new ApiRequestEvent('test-model', 'This is a test request');
 
       logApiRequest(mockConfig, event);
 
@@ -262,9 +293,7 @@ describe('loggers', () => {
     });
 
     it('should log an API request without request_text', () => {
-      const event = {
-        model: 'test-model',
-      };
+      const event = new ApiRequestEvent('test-model');
 
       logApiRequest(mockConfig, event);
 
@@ -281,8 +310,46 @@ describe('loggers', () => {
   });
 
   describe('logToolCall', () => {
+    const cfg1 = {
+      getSessionId: () => 'test-session-id',
+      getTargetDir: () => 'target-dir',
+      getGeminiClient: () => mockGeminiClient,
+    } as Config;
+    const cfg2 = {
+      getSessionId: () => 'test-session-id',
+      getTargetDir: () => 'target-dir',
+      getProxy: () => 'http://test.proxy.com:8080',
+      getContentGeneratorConfig: () =>
+        ({ model: 'test-model' }) as ContentGeneratorConfig,
+      getModel: () => 'test-model',
+      getEmbeddingModel: () => 'test-embedding-model',
+      getWorkingDir: () => 'test-working-dir',
+      getSandbox: () => true,
+      getCoreTools: () => ['ls', 'read-file'],
+      getApprovalMode: () => 'default',
+      getTelemetryLogPromptsEnabled: () => true,
+      getFileFilteringRespectGitIgnore: () => true,
+      getFileFilteringAllowBuildArtifacts: () => false,
+      getDebugMode: () => true,
+      getMcpServers: () => ({
+        'test-server': {
+          command: 'test-command',
+        },
+      }),
+      getQuestion: () => 'test-question',
+      getToolRegistry: () => new ToolRegistry(cfg1),
+      getFullContext: () => false,
+      getUserMemory: () => 'user-memory',
+    } as unknown as Config;
+
+    const mockGeminiClient = new GeminiClient(cfg2);
     const mockConfig = {
       getSessionId: () => 'test-session-id',
+      getTargetDir: () => 'target-dir',
+      getGeminiClient: () => mockGeminiClient,
+      getDisableDataCollection: () => false,
+      getTelemetryEnabled: () => true,
+      getTelemetryLogPromptsEnabled: () => true,
     } as Config;
 
     const mockMetrics = {
@@ -297,23 +364,36 @@ describe('loggers', () => {
     });
 
     it('should log a tool call with all fields', () => {
-      const event = {
-        function_name: 'test-function',
-        function_args: {
-          arg1: 'value1',
-          arg2: 2,
+      const call: CompletedToolCall = {
+        status: 'success',
+        request: {
+          name: 'test-function',
+          args: {
+            arg1: 'value1',
+            arg2: 2,
+          },
+          callId: 'test-call-id',
+          isClientInitiated: true,
+        },
+        response: {
+          callId: 'test-call-id',
+          responseParts: 'test-response',
+          resultDisplay: undefined,
+          error: undefined,
         },
-        duration_ms: 100,
-        success: true,
+        tool: new EditTool(mockConfig),
+        durationMs: 100,
+        outcome: ToolConfirmationOutcome.ProceedOnce,
       };
+      const event = new ToolCallEvent(call);
 
-      logToolCall(mockConfig, event, ToolConfirmationOutcome.ProceedOnce);
+      logToolCall(mockConfig, event);
 
       expect(mockLogger.emit).toHaveBeenCalledWith({
         body: 'Tool call: test-function. Decision: accept. Success: true. Duration: 100ms.',
         attributes: {
           'session.id': 'test-session-id',
-          'event.name': 'gemini_cli.tool_call',
+          'event.name': EVENT_TOOL_CALL,
           'event.timestamp': '2025-01-01T00:00:00.000Z',
           function_name: 'test-function',
           function_args: JSON.stringify(
@@ -339,23 +419,35 @@ describe('loggers', () => {
       );
     });
     it('should log a tool call with a reject decision', () => {
-      const event = {
-        function_name: 'test-function',
-        function_args: {
-          arg1: 'value1',
-          arg2: 2,
+      const call: ErroredToolCall = {
+        status: 'error',
+        request: {
+          name: 'test-function',
+          args: {
+            arg1: 'value1',
+            arg2: 2,
+          },
+          callId: 'test-call-id',
+          isClientInitiated: true,
+        },
+        response: {
+          callId: 'test-call-id',
+          responseParts: 'test-response',
+          resultDisplay: undefined,
+          error: undefined,
         },
-        duration_ms: 100,
-        success: false,
+        durationMs: 100,
+        outcome: ToolConfirmationOutcome.Cancel,
       };
+      const event = new ToolCallEvent(call);
 
-      logToolCall(mockConfig, event, ToolConfirmationOutcome.Cancel);
+      logToolCall(mockConfig, event);
 
       expect(mockLogger.emit).toHaveBeenCalledWith({
         body: 'Tool call: test-function. Decision: reject. Success: false. Duration: 100ms.',
         attributes: {
           'session.id': 'test-session-id',
-          'event.name': 'gemini_cli.tool_call',
+          'event.name': EVENT_TOOL_CALL,
           'event.timestamp': '2025-01-01T00:00:00.000Z',
           function_name: 'test-function',
           function_args: JSON.stringify(
@@ -382,23 +474,36 @@ describe('loggers', () => {
     });
 
     it('should log a tool call with a modify decision', () => {
-      const event = {
-        function_name: 'test-function',
-        function_args: {
-          arg1: 'value1',
-          arg2: 2,
+      const call: CompletedToolCall = {
+        status: 'success',
+        request: {
+          name: 'test-function',
+          args: {
+            arg1: 'value1',
+            arg2: 2,
+          },
+          callId: 'test-call-id',
+          isClientInitiated: true,
         },
-        duration_ms: 100,
-        success: true,
+        response: {
+          callId: 'test-call-id',
+          responseParts: 'test-response',
+          resultDisplay: undefined,
+          error: undefined,
+        },
+        outcome: ToolConfirmationOutcome.ModifyWithEditor,
+        tool: new EditTool(mockConfig),
+        durationMs: 100,
       };
+      const event = new ToolCallEvent(call);
 
-      logToolCall(mockConfig, event, ToolConfirmationOutcome.ModifyWithEditor);
+      logToolCall(mockConfig, event);
 
       expect(mockLogger.emit).toHaveBeenCalledWith({
         body: 'Tool call: test-function. Decision: modify. Success: true. Duration: 100ms.',
         attributes: {
           'session.id': 'test-session-id',
-          'event.name': 'gemini_cli.tool_call',
+          'event.name': EVENT_TOOL_CALL,
           'event.timestamp': '2025-01-01T00:00:00.000Z',
           function_name: 'test-function',
           function_args: JSON.stringify(
@@ -425,15 +530,27 @@ describe('loggers', () => {
     });
 
     it('should log a tool call without a decision', () => {
-      const event = {
-        function_name: 'test-function',
-        function_args: {
-          arg1: 'value1',
-          arg2: 2,
+      const call: CompletedToolCall = {
+        status: 'success',
+        request: {
+          name: 'test-function',
+          args: {
+            arg1: 'value1',
+            arg2: 2,
+          },
+          callId: 'test-call-id',
+          isClientInitiated: true,
+        },
+        response: {
+          callId: 'test-call-id',
+          responseParts: 'test-response',
+          resultDisplay: undefined,
+          error: undefined,
         },
-        duration_ms: 100,
-        success: true,
+        tool: new EditTool(mockConfig),
+        durationMs: 100,
       };
+      const event = new ToolCallEvent(call);
 
       logToolCall(mockConfig, event);
 
@@ -441,7 +558,7 @@ describe('loggers', () => {
         body: 'Tool call: test-function. Success: true. Duration: 100ms.',
         attributes: {
           'session.id': 'test-session-id',
-          'event.name': 'gemini_cli.tool_call',
+          'event.name': EVENT_TOOL_CALL,
           'event.timestamp': '2025-01-01T00:00:00.000Z',
           function_name: 'test-function',
           function_args: JSON.stringify(
@@ -467,17 +584,29 @@ describe('loggers', () => {
     });
 
     it('should log a failed tool call with an error', () => {
-      const event = {
-        function_name: 'test-function',
-        function_args: {
-          arg1: 'value1',
-          arg2: 2,
+      const call: ErroredToolCall = {
+        status: 'error',
+        request: {
+          name: 'test-function',
+          args: {
+            arg1: 'value1',
+            arg2: 2,
+          },
+          callId: 'test-call-id',
+          isClientInitiated: true,
+        },
+        response: {
+          callId: 'test-call-id',
+          responseParts: 'test-response',
+          resultDisplay: undefined,
+          error: {
+            name: 'test-error-type',
+            message: 'test-error',
+          },
         },
-        duration_ms: 100,
-        success: false,
-        error: 'test-error',
-        error_type: 'test-error-type',
+        durationMs: 100,
       };
+      const event = new ToolCallEvent(call);
 
       logToolCall(mockConfig, event);
 
@@ -485,7 +614,7 @@ describe('loggers', () => {
         body: 'Tool call: test-function. Success: false. Duration: 100ms.',
         attributes: {
           'session.id': 'test-session-id',
-          'event.name': 'gemini_cli.tool_call',
+          'event.name': EVENT_TOOL_CALL,
           'event.timestamp': '2025-01-01T00:00:00.000Z',
           function_name: 'test-function',
           function_args: JSON.stringify(
@@ -515,75 +644,3 @@ describe('loggers', () => {
     });
   });
 });
-
-describe('getFinalUsageMetadata', () => {
-  const createMockResponse = (
-    usageMetadata?: GenerateContentResponse['usageMetadata'],
-  ): GenerateContentResponse =>
-    ({
-      text: () => '',
-      data: () => ({}) as Record<string, unknown>,
-      functionCalls: () => [],
-      executableCode: () => [],
-      codeExecutionResult: () => [],
-      usageMetadata,
-    }) as unknown as GenerateContentResponse;
-
-  it('should return the usageMetadata from the last chunk that has it', () => {
-    const chunks: GenerateContentResponse[] = [
-      createMockResponse({
-        promptTokenCount: 10,
-        candidatesTokenCount: 20,
-        totalTokenCount: 30,
-      }),
-      createMockResponse(),
-      createMockResponse({
-        promptTokenCount: 15,
-        candidatesTokenCount: 25,
-        totalTokenCount: 40,
-      }),
-      createMockResponse(),
-    ];
-
-    const result = getFinalUsageMetadata(chunks);
-    expect(result).toEqual({
-      promptTokenCount: 15,
-      candidatesTokenCount: 25,
-      totalTokenCount: 40,
-    });
-  });
-
-  it('should return undefined if no chunks have usageMetadata', () => {
-    const chunks: GenerateContentResponse[] = [
-      createMockResponse(),
-      createMockResponse(),
-      createMockResponse(),
-    ];
-
-    const result = getFinalUsageMetadata(chunks);
-    expect(result).toBeUndefined();
-  });
-
-  it('should return the metadata from the only chunk if it has it', () => {
-    const chunks: GenerateContentResponse[] = [
-      createMockResponse({
-        promptTokenCount: 1,
-        candidatesTokenCount: 2,
-        totalTokenCount: 3,
-      }),
-    ];
-
-    const result = getFinalUsageMetadata(chunks);
-    expect(result).toEqual({
-      promptTokenCount: 1,
-      candidatesTokenCount: 2,
-      totalTokenCount: 3,
-    });
-  });
-
-  it('should return undefined for an empty array of chunks', () => {
-    const chunks: GenerateContentResponse[] = [];
-    const result = getFinalUsageMetadata(chunks);
-    expect(result).toBeUndefined();
-  });
-});
diff --git a/packages/core/src/telemetry/loggers.ts b/packages/core/src/telemetry/loggers.ts
index 0ecf130f..054386b8 100644
--- a/packages/core/src/telemetry/loggers.ts
+++ b/packages/core/src/telemetry/loggers.ts
@@ -20,6 +20,7 @@ import {
   ApiErrorEvent,
   ApiRequestEvent,
   ApiResponseEvent,
+  StartSessionEvent,
   ToolCallEvent,
   UserPromptEvent,
 } from './types.js';
@@ -30,15 +31,10 @@ import {
   recordToolCallMetrics,
 } from './metrics.js';
 import { isTelemetrySdkInitialized } from './sdk.js';
-import { ToolConfirmationOutcome } from '../tools/tools.js';
-import {
-  GenerateContentResponse,
-  GenerateContentResponseUsageMetadata,
-} from '@google/genai';
-import { AuthType } from '../core/contentGenerator.js';
+import { ClearcutLogger } from './clearcut-logger/clearcut-logger.js';
 
 const shouldLogUserPrompts = (config: Config): boolean =>
-  config.getTelemetryLogPromptsEnabled() ?? false;
+  config.getTelemetryLogPromptsEnabled();
 
 function getCommonAttributes(config: Config): LogAttributes {
   return {
@@ -46,59 +42,30 @@ function getCommonAttributes(config: Config): LogAttributes {
   };
 }
 
-export enum ToolCallDecision {
-  ACCEPT = 'accept',
-  REJECT = 'reject',
-  MODIFY = 'modify',
-}
-
-export function getDecisionFromOutcome(
-  outcome: ToolConfirmationOutcome,
-): ToolCallDecision {
-  switch (outcome) {
-    case ToolConfirmationOutcome.ProceedOnce:
-    case ToolConfirmationOutcome.ProceedAlways:
-    case ToolConfirmationOutcome.ProceedAlwaysServer:
-    case ToolConfirmationOutcome.ProceedAlwaysTool:
-      return ToolCallDecision.ACCEPT;
-    case ToolConfirmationOutcome.ModifyWithEditor:
-      return ToolCallDecision.MODIFY;
-    case ToolConfirmationOutcome.Cancel:
-    default:
-      return ToolCallDecision.REJECT;
-  }
-}
-
-export function logCliConfiguration(config: Config): void {
+export function logCliConfiguration(
+  config: Config,
+  event: StartSessionEvent,
+): void {
+  ClearcutLogger.getInstance(config)?.logStartSessionEvent(event);
   if (!isTelemetrySdkInitialized()) return;
 
-  const generatorConfig = config.getContentGeneratorConfig();
-  let useGemini = false;
-  let useVertex = false;
-
-  if (generatorConfig && generatorConfig.authType) {
-    useGemini = generatorConfig.authType === AuthType.USE_GEMINI;
-    useVertex = generatorConfig.authType === AuthType.USE_VERTEX_AI;
-  }
-
-  const mcpServers = config.getMcpServers();
   const attributes: LogAttributes = {
     ...getCommonAttributes(config),
     'event.name': EVENT_CLI_CONFIG,
     'event.timestamp': new Date().toISOString(),
-    model: config.getModel(),
-    embedding_model: config.getEmbeddingModel(),
-    sandbox_enabled: !!config.getSandbox(),
-    core_tools_enabled: (config.getCoreTools() ?? []).join(','),
-    approval_mode: config.getApprovalMode(),
-    api_key_enabled: useGemini || useVertex,
-    vertex_ai_enabled: useVertex,
-    log_user_prompts_enabled: config.getTelemetryLogPromptsEnabled(),
-    file_filtering_respect_git_ignore:
-      config.getFileFilteringRespectGitIgnore(),
-    debug_mode: config.getDebugMode(),
-    mcp_servers: mcpServers ? Object.keys(mcpServers).join(',') : '',
+    model: event.model,
+    embedding_model: event.embedding_model,
+    sandbox_enabled: event.sandbox_enabled,
+    core_tools_enabled: event.core_tools_enabled,
+    approval_mode: event.approval_mode,
+    api_key_enabled: event.api_key_enabled,
+    vertex_ai_enabled: event.vertex_ai_enabled,
+    log_user_prompts_enabled: event.telemetry_log_user_prompts_enabled,
+    file_filtering_respect_git_ignore: event.file_filtering_respect_git_ignore,
+    debug_mode: event.debug_enabled,
+    mcp_servers: event.mcp_servers,
   };
+
   const logger = logs.getLogger(SERVICE_NAME);
   const logRecord: LogRecord = {
     body: 'CLI configuration loaded.',
@@ -107,12 +74,8 @@ export function logCliConfiguration(config: Config): void {
   logger.emit(logRecord);
 }
 
-export function logUserPrompt(
-  config: Config,
-  event: Omit<UserPromptEvent, 'event.name' | 'event.timestamp' | 'prompt'> & {
-    prompt: string;
-  },
-): void {
+export function logUserPrompt(config: Config, event: UserPromptEvent): void {
+  ClearcutLogger.getInstance(config)?.logNewPromptEvent(event);
   if (!isTelemetrySdkInitialized()) return;
 
   const attributes: LogAttributes = {
@@ -134,22 +97,16 @@ export function logUserPrompt(
   logger.emit(logRecord);
 }
 
-export function logToolCall(
-  config: Config,
-  event: Omit<ToolCallEvent, 'event.name' | 'event.timestamp' | 'decision'>,
-  outcome?: ToolConfirmationOutcome,
-): void {
+export function logToolCall(config: Config, event: ToolCallEvent): void {
+  ClearcutLogger.getInstance(config)?.logToolCallEvent(event);
   if (!isTelemetrySdkInitialized()) return;
 
-  const decision = outcome ? getDecisionFromOutcome(outcome) : undefined;
-
   const attributes: LogAttributes = {
     ...getCommonAttributes(config),
     ...event,
     'event.name': EVENT_TOOL_CALL,
     'event.timestamp': new Date().toISOString(),
     function_args: JSON.stringify(event.function_args, null, 2),
-    decision,
   };
   if (event.error) {
     attributes['error.message'] = event.error;
@@ -157,9 +114,10 @@ export function logToolCall(
       attributes['error.type'] = event.error_type;
     }
   }
+
   const logger = logs.getLogger(SERVICE_NAME);
   const logRecord: LogRecord = {
-    body: `Tool call: ${event.function_name}${decision ? `. Decision: ${decision}` : ''}. Success: ${event.success}. Duration: ${event.duration_ms}ms.`,
+    body: `Tool call: ${event.function_name}${event.decision ? `. Decision: ${event.decision}` : ''}. Success: ${event.success}. Duration: ${event.duration_ms}ms.`,
     attributes,
   };
   logger.emit(logRecord);
@@ -168,21 +126,21 @@ export function logToolCall(
     event.function_name,
     event.duration_ms,
     event.success,
-    decision,
+    event.decision,
   );
 }
 
-export function logApiRequest(
-  config: Config,
-  event: Omit<ApiRequestEvent, 'event.name' | 'event.timestamp'>,
-): void {
+export function logApiRequest(config: Config, event: ApiRequestEvent): void {
+  ClearcutLogger.getInstance(config)?.logApiRequestEvent(event);
   if (!isTelemetrySdkInitialized()) return;
+
   const attributes: LogAttributes = {
     ...getCommonAttributes(config),
     ...event,
     'event.name': EVENT_API_REQUEST,
     'event.timestamp': new Date().toISOString(),
   };
+
   const logger = logs.getLogger(SERVICE_NAME);
   const logRecord: LogRecord = {
     body: `API request to ${event.model}.`,
@@ -191,17 +149,18 @@ export function logApiRequest(
   logger.emit(logRecord);
 }
 
-export function logApiError(
-  config: Config,
-  event: Omit<ApiErrorEvent, 'event.name' | 'event.timestamp'>,
-): void {
+export function logApiError(config: Config, event: ApiErrorEvent): void {
+  ClearcutLogger.getInstance(config)?.logApiErrorEvent(event);
   if (!isTelemetrySdkInitialized()) return;
+
   const attributes: LogAttributes = {
     ...getCommonAttributes(config),
     ...event,
     'event.name': EVENT_API_ERROR,
     'event.timestamp': new Date().toISOString(),
     ['error.message']: event.error,
+    model_name: event.model,
+    duration: event.duration_ms,
   };
 
   if (event.error_type) {
@@ -226,10 +185,8 @@ export function logApiError(
   );
 }
 
-export function logApiResponse(
-  config: Config,
-  event: Omit<ApiResponseEvent, 'event.name' | 'event.timestamp'>,
-): void {
+export function logApiResponse(config: Config, event: ApiResponseEvent): void {
+  ClearcutLogger.getInstance(config)?.logApiResponseEvent(event);
   if (!isTelemetrySdkInitialized()) return;
   const attributes: LogAttributes = {
     ...getCommonAttributes(config),
@@ -287,15 +244,3 @@ export function logApiResponse(
   );
   recordTokenUsageMetrics(config, event.model, event.tool_token_count, 'tool');
 }
-
-export function getFinalUsageMetadata(
-  chunks: GenerateContentResponse[],
-): GenerateContentResponseUsageMetadata | undefined {
-  // Only the last streamed item has the final token count.
-  const lastChunkWithMetadata = chunks
-    .slice()
-    .reverse()
-    .find((chunk) => chunk.usageMetadata);
-
-  return lastChunkWithMetadata?.usageMetadata;
-}
diff --git a/packages/core/src/telemetry/sdk.ts b/packages/core/src/telemetry/sdk.ts
index 61f501a6..033a9d77 100644
--- a/packages/core/src/telemetry/sdk.ts
+++ b/packages/core/src/telemetry/sdk.ts
@@ -29,6 +29,8 @@ import { Config } from '../config/config.js';
 import { SERVICE_NAME } from './constants.js';
 import { initializeMetrics } from './metrics.js';
 import { logCliConfiguration } from './loggers.js';
+import { StartSessionEvent } from './types.js';
+import { ClearcutLogger } from './clearcut-logger/clearcut-logger.js';
 
 // For troubleshooting, set the log level to DiagLogLevel.DEBUG
 diag.setLogger(new DiagConsoleLogger(), DiagLogLevel.INFO);
@@ -113,7 +115,7 @@ export function initializeTelemetry(config: Config): void {
     console.log('OpenTelemetry SDK started successfully.');
     telemetryInitialized = true;
     initializeMetrics(config);
-    logCliConfiguration(config);
+    logCliConfiguration(config, new StartSessionEvent(config));
   } catch (error) {
     console.error('Error starting OpenTelemetry SDK:', error);
   }
@@ -127,6 +129,7 @@ export async function shutdownTelemetry(): Promise<void> {
     return;
   }
   try {
+    ClearcutLogger.getInstance()?.shutdown();
     await sdk.shutdown();
     console.log('OpenTelemetry SDK shut down successfully.');
   } catch (error) {
diff --git a/packages/core/src/telemetry/telemetry.test.ts b/packages/core/src/telemetry/telemetry.test.ts
index 97c96c64..624c9ded 100644
--- a/packages/core/src/telemetry/telemetry.test.ts
+++ b/packages/core/src/telemetry/telemetry.test.ts
@@ -13,6 +13,7 @@ import {
 import { Config } from '../config/config.js';
 import { NodeSDK } from '@opentelemetry/sdk-node';
 import * as loggers from './loggers.js';
+import { StartSessionEvent } from './types.js';
 
 vi.mock('@opentelemetry/sdk-node');
 vi.mock('../config/config.js');
@@ -55,10 +56,11 @@ describe('telemetry', () => {
 
   it('should initialize the telemetry service', () => {
     initializeTelemetry(mockConfig);
+    const event = new StartSessionEvent(mockConfig);
 
     expect(NodeSDK).toHaveBeenCalled();
     expect(mockNodeSdk.start).toHaveBeenCalled();
-    expect(loggers.logCliConfiguration).toHaveBeenCalledWith(mockConfig);
+    expect(loggers.logCliConfiguration).toHaveBeenCalledWith(mockConfig, event);
   });
 
   it('should shutdown the telemetry service', async () => {
diff --git a/packages/core/src/telemetry/types.ts b/packages/core/src/telemetry/types.ts
index 68dd411e..f70daa78 100644
--- a/packages/core/src/telemetry/types.ts
+++ b/packages/core/src/telemetry/types.ts
@@ -4,16 +4,108 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { ToolCallDecision } from './loggers.js';
+import { GenerateContentResponseUsageMetadata } from '@google/genai';
+import { Config } from '../config/config.js';
+import { CompletedToolCall } from '../core/coreToolScheduler.js';
+import { ToolConfirmationOutcome } from '../tools/tools.js';
+import { AuthType } from '../core/contentGenerator.js';
 
-export interface UserPromptEvent {
+export enum ToolCallDecision {
+  ACCEPT = 'accept',
+  REJECT = 'reject',
+  MODIFY = 'modify',
+}
+
+export function getDecisionFromOutcome(
+  outcome: ToolConfirmationOutcome,
+): ToolCallDecision {
+  switch (outcome) {
+    case ToolConfirmationOutcome.ProceedOnce:
+    case ToolConfirmationOutcome.ProceedAlways:
+    case ToolConfirmationOutcome.ProceedAlwaysServer:
+    case ToolConfirmationOutcome.ProceedAlwaysTool:
+      return ToolCallDecision.ACCEPT;
+    case ToolConfirmationOutcome.ModifyWithEditor:
+      return ToolCallDecision.MODIFY;
+    case ToolConfirmationOutcome.Cancel:
+    default:
+      return ToolCallDecision.REJECT;
+  }
+}
+
+export class StartSessionEvent {
+  'event.name': 'cli_config';
+  'event.timestamp': string; // ISO 8601
+  model: string;
+  embedding_model: string;
+  sandbox_enabled: boolean;
+  core_tools_enabled: string;
+  approval_mode: string;
+  api_key_enabled: boolean;
+  vertex_ai_enabled: boolean;
+  debug_enabled: boolean;
+  mcp_servers: string;
+  telemetry_enabled: boolean;
+  telemetry_log_user_prompts_enabled: boolean;
+  file_filtering_respect_git_ignore: boolean;
+
+  constructor(config: Config) {
+    const generatorConfig = config.getContentGeneratorConfig();
+    const mcpServers = config.getMcpServers();
+
+    let useGemini = false;
+    let useVertex = false;
+    if (generatorConfig && generatorConfig.authType) {
+      useGemini = generatorConfig.authType === AuthType.USE_GEMINI;
+      useVertex = generatorConfig.authType === AuthType.USE_VERTEX_AI;
+    }
+
+    this['event.name'] = 'cli_config';
+    this.model = config.getModel();
+    this.embedding_model = config.getEmbeddingModel();
+    this.sandbox_enabled =
+      typeof config.getSandbox() === 'string' || !!config.getSandbox();
+    this.core_tools_enabled = (config.getCoreTools() ?? []).join(',');
+    this.approval_mode = config.getApprovalMode();
+    this.api_key_enabled = useGemini || useVertex;
+    this.vertex_ai_enabled = useVertex;
+    this.debug_enabled = config.getDebugMode();
+    this.mcp_servers = mcpServers ? Object.keys(mcpServers).join(',') : '';
+    this.telemetry_enabled = config.getTelemetryEnabled();
+    this.telemetry_log_user_prompts_enabled =
+      config.getTelemetryLogPromptsEnabled();
+    this.file_filtering_respect_git_ignore =
+      config.getFileFilteringRespectGitIgnore();
+  }
+}
+
+export class EndSessionEvent {
+  'event.name': 'end_session';
+  'event.timestamp': string; // ISO 8601
+  session_id?: string;
+
+  constructor(config?: Config) {
+    this['event.name'] = 'end_session';
+    this['event.timestamp'] = new Date().toISOString();
+    this.session_id = config?.getSessionId();
+  }
+}
+
+export class UserPromptEvent {
   'event.name': 'user_prompt';
   'event.timestamp': string; // ISO 8601
   prompt_length: number;
   prompt?: string;
+
+  constructor(prompt_length: number, prompt?: string) {
+    this['event.name'] = 'user_prompt';
+    this['event.timestamp'] = new Date().toISOString();
+    this.prompt_length = prompt_length;
+    this.prompt = prompt;
+  }
 }
 
-export interface ToolCallEvent {
+export class ToolCallEvent {
   'event.name': 'tool_call';
   'event.timestamp': string; // ISO 8601
   function_name: string;
@@ -23,16 +115,37 @@ export interface ToolCallEvent {
   decision?: ToolCallDecision;
   error?: string;
   error_type?: string;
+
+  constructor(call: CompletedToolCall) {
+    this['event.name'] = 'tool_call';
+    this['event.timestamp'] = new Date().toISOString();
+    this.function_name = call.request.name;
+    this.function_args = call.request.args;
+    this.duration_ms = call.durationMs ?? 0;
+    this.success = call.status === 'success';
+    this.decision = call.outcome
+      ? getDecisionFromOutcome(call.outcome)
+      : undefined;
+    this.error = call.response.error?.message;
+    this.error_type = call.response.error?.name;
+  }
 }
 
-export interface ApiRequestEvent {
+export class ApiRequestEvent {
   'event.name': 'api_request';
   'event.timestamp': string; // ISO 8601
   model: string;
   request_text?: string;
+
+  constructor(model: string, request_text?: string) {
+    this['event.name'] = 'api_request';
+    this['event.timestamp'] = new Date().toISOString();
+    this.model = model;
+    this.request_text = request_text;
+  }
 }
 
-export interface ApiErrorEvent {
+export class ApiErrorEvent {
   'event.name': 'api_error';
   'event.timestamp': string; // ISO 8601
   model: string;
@@ -40,9 +153,25 @@ export interface ApiErrorEvent {
   error_type?: string;
   status_code?: number | string;
   duration_ms: number;
+
+  constructor(
+    model: string,
+    error: string,
+    duration_ms: number,
+    error_type?: string,
+    status_code?: number | string,
+  ) {
+    this['event.name'] = 'api_error';
+    this['event.timestamp'] = new Date().toISOString();
+    this.model = model;
+    this.error = error;
+    this.error_type = error_type;
+    this.status_code = status_code;
+    this.duration_ms = duration_ms;
+  }
 }
 
-export interface ApiResponseEvent {
+export class ApiResponseEvent {
   'event.name': 'api_response';
   'event.timestamp': string; // ISO 8601
   model: string;
@@ -55,24 +184,34 @@ export interface ApiResponseEvent {
   thoughts_token_count: number;
   tool_token_count: number;
   response_text?: string;
-}
 
-export interface CliConfigEvent {
-  'event.name': 'cli_config';
-  'event.timestamp': string; // ISO 8601
-  model: string;
-  sandbox_enabled: boolean;
-  core_tools_enabled: string;
-  approval_mode: string;
-  vertex_ai_enabled: boolean;
-  log_user_prompts_enabled: boolean;
-  file_filtering_respect_git_ignore: boolean;
+  constructor(
+    model: string,
+    duration_ms: number,
+    usage_data?: GenerateContentResponseUsageMetadata,
+    response_text?: string,
+    error?: string,
+  ) {
+    this['event.name'] = 'api_response';
+    this['event.timestamp'] = new Date().toISOString();
+    this.model = model;
+    this.duration_ms = duration_ms;
+    this.status_code = 200;
+    this.input_token_count = usage_data?.promptTokenCount ?? 0;
+    this.output_token_count = usage_data?.candidatesTokenCount ?? 0;
+    this.cached_content_token_count = usage_data?.cachedContentTokenCount ?? 0;
+    this.thoughts_token_count = usage_data?.thoughtsTokenCount ?? 0;
+    this.tool_token_count = usage_data?.toolUsePromptTokenCount ?? 0;
+    this.response_text = response_text;
+    this.error = error;
+  }
 }
 
 export type TelemetryEvent =
+  | StartSessionEvent
+  | EndSessionEvent
   | UserPromptEvent
   | ToolCallEvent
   | ApiRequestEvent
   | ApiErrorEvent
-  | ApiResponseEvent
-  | CliConfigEvent;
+  | ApiResponseEvent;
diff --git a/packages/core/src/utils/user_id.ts b/packages/core/src/utils/user_id.ts
new file mode 100644
index 00000000..5db080a4
--- /dev/null
+++ b/packages/core/src/utils/user_id.ts
@@ -0,0 +1,58 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as os from 'os';
+import * as fs from 'fs';
+import * as path from 'path';
+import { randomUUID } from 'crypto';
+import { GEMINI_DIR } from './paths.js';
+
+const homeDir = os.homedir() ?? '';
+const geminiDir = path.join(homeDir, GEMINI_DIR);
+const userIdFile = path.join(geminiDir, 'user_id');
+
+function ensureGeminiDirExists() {
+  if (!fs.existsSync(geminiDir)) {
+    fs.mkdirSync(geminiDir, { recursive: true });
+  }
+}
+
+function readUserIdFromFile(): string | null {
+  if (fs.existsSync(userIdFile)) {
+    const userId = fs.readFileSync(userIdFile, 'utf-8').trim();
+    return userId || null;
+  }
+  return null;
+}
+
+function writeUserIdToFile(userId: string) {
+  fs.writeFileSync(userIdFile, userId, 'utf-8');
+}
+
+/**
+ * Retrieves the persistent user ID from a file, creating it if it doesn't exist.
+ * This ID is used for unique user tracking.
+ * @returns A UUID string for the user.
+ */
+export function getPersistentUserId(): string {
+  try {
+    ensureGeminiDirExists();
+    let userId = readUserIdFromFile();
+
+    if (!userId) {
+      userId = randomUUID();
+      writeUserIdToFile(userId);
+    }
+
+    return userId;
+  } catch (error) {
+    console.error(
+      'Error accessing persistent user ID file, generating ephemeral ID:',
+      error,
+    );
+    return '123456789';
+  }
+}