@@ -27,6 +27,10 @@ Work in this release was contributed by @adityareddy-dev, @jpdefo, @Jxxunnn, @ph
 
   `ignoreStaticAssets` defaults to `true`, so `Deno.serve` no longer creates spans for `GET` requests to common static assets such as `favicon.ico`, `robots.txt` or `*.js` files. To keep these spans, set `denoServeIntegration({ ignoreStaticAssets: false })`. `Deno.serve` spans also follow the client's tracing configuration by default, so the integration does not start spans when tracing is disabled.
 
+- **feat(deno): Record request sessions for `Deno.serve`**
+
+  `denoServeIntegration` now records a request session for each incoming request, as `denoHttpIntegration` does for `node:http`. This gives release health and crash-free rates for `Deno.serve` apps. Sessions are sent only when a `release` is set. To turn them off, set `denoServeIntegration({ sessions: false })`. `sessionFlushingDelayMS` sets how long the SDK waits before it sends the session aggregate.
+
 ## 11.8.0
 
 ### Important Changes
 
@@ -33,6 +33,29 @@ export function recordRequestSession(
     sessionFlushingDelayMS?: number;
   },
 ): void {
+  response.once('close', startRequestSession(client, { requestIsolationScope, sessionFlushingDelayMS }));
+}
+
+/**
+ * Starts a session and tracks it in the context of a given isolation scope.
+ * Returns a function to call when the request ends. It puts the session into
+ * a task, which aggregates it with other sessions in a certain time window
+ * (sessionFlushingDelayMs, 60 seconds by default). Calls after the first
+ * one do nothing.
+ *
+ * Use this when the server has no `node:http` response to pass to
+ * {@link recordRequestSession}.
+ */
+export function startRequestSession(
+  client: Client,
+  {
+    requestIsolationScope,
+    sessionFlushingDelayMS = 60_000,
+  }: {
+    requestIsolationScope: Scope;
+    sessionFlushingDelayMS?: number;
+  },
+): () => void {
   // Errors in this request are counted by the request session aggregate, so they must not also
   // update a process session inherited from the parent isolation scope.
   requestIsolationScope.setSession();
@@ -41,7 +64,12 @@ export function recordRequestSession(
   });
   client.emit('startRequestSession');
 
-  response.once('close', () => {
+  let ended = false;
+  return () => {
+    if (ended) {
+      return;
+    }
+    ended = true;
     const requestSession = requestIsolationScope.getScopeData().sdkProcessingMetadata.requestSession;
 
     if (client && requestSession) {
@@ -89,5 +117,5 @@ export function recordRequestSession(
         safeUnref(timeout);
       }
     }
-  });
+  };
 }
@@ -22,7 +22,7 @@ export {
   DEFAULT_IGNORE_STATUS_CODES,
   processHttpServerTransactionEvent,
 } from './integrations/http/server-transaction-event';
-export { recordRequestSession } from './integrations/http/record-request-session';
+export { recordRequestSession, startRequestSession } from './integrations/http/record-request-session';
 export { getClientIPAddress } from './utils/clientIPAddress';
 export { addOutgoingRequestBreadcrumb } from './integrations/http/add-outgoing-request-breadcrumb';
 export {
 
@@ -0,0 +1,129 @@
+import { EventEmitter } from 'node:events';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { recordRequestSession, startRequestSession } from '../../../../src/integrations/http/record-request-session';
+import { Scope } from '../../../../src/scope';
+import { getDefaultTestClientOptions, TestClient } from '../../../mocks/client';
+
+function createTestClient(): TestClient {
+  return new TestClient(getDefaultTestClientOptions({ release: '1.0.0' }));
+}
+
+describe('startRequestSession()', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('March 19, 1999 06:12:34 UTC'));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('counts the session when end() is called', () => {
+    const client = createTestClient();
+    const sendSessionSpy = vi.spyOn(client, 'sendSession');
+    const requestIsolationScope = new Scope();
+
+    const end = startRequestSession(client, { requestIsolationScope });
+    vi.runAllTimers();
+    expect(sendSessionSpy).not.toHaveBeenCalled();
+
+    end();
+    vi.runAllTimers();
+
+    expect(sendSessionSpy).toHaveBeenCalledWith({
+      aggregates: [{ crashed: 0, errored: 0, exited: 1, started: '1999-03-19T06:12:00.000Z' }],
+    });
+  });
+
+  it('counts the status set on the request isolation scope before end()', () => {
+    const client = createTestClient();
+    const sendSessionSpy = vi.spyOn(client, 'sendSession');
+    const requestIsolationScope = new Scope();
+
+    const end = startRequestSession(client, { requestIsolationScope });
+    requestIsolationScope.getScopeData().sdkProcessingMetadata.requestSession!.status = 'crashed';
+    end();
+    vi.runAllTimers();
+
+    expect(sendSessionSpy).toHaveBeenCalledWith({
+      aggregates: [{ crashed: 1, errored: 0, exited: 0, started: '1999-03-19T06:12:00.000Z' }],
+    });
+  });
+
+  it('counts a session once when end() is called more than once', () => {
+    const client = createTestClient();
+    const sendSessionSpy = vi.spyOn(client, 'sendSession');
+    const requestIsolationScope = new Scope();
+
+    const end = startRequestSession(client, { requestIsolationScope });
+    end();
+    end();
+    vi.runAllTimers();
+
+    expect(sendSessionSpy).toHaveBeenCalledTimes(1);
+    expect(sendSessionSpy).toHaveBeenCalledWith({
+      aggregates: [{ crashed: 0, errored: 0, exited: 1, started: '1999-03-19T06:12:00.000Z' }],
+    });
+  });
+
+  it('emits the "startRequestSession" hook when the session starts', () => {
+    const client = createTestClient();
+    const onStartRequestSession = vi.fn();
+    client.on('startRequestSession', onStartRequestSession);
+
+    startRequestSession(client, { requestIsolationScope: new Scope() });
+
+    expect(onStartRequestSession).toHaveBeenCalledTimes(1);
+  });
+
+  it('uses sessionFlushingDelayMS to schedule the aggregate', () => {
+    const client = createTestClient();
+    const sendSessionSpy = vi.spyOn(client, 'sendSession');
+
+    startRequestSession(client, { requestIsolationScope: new Scope(), sessionFlushingDelayMS: 1_000 })();
+
+    vi.advanceTimersByTime(999);
+    expect(sendSessionSpy).not.toHaveBeenCalled();
+    vi.advanceTimersByTime(1);
+    expect(sendSessionSpy).toHaveBeenCalledTimes(1);
+  });
+  it('sends the aggregate after 60 seconds by default', () => {
+    const client = createTestClient();
+    const sendSessionSpy = vi.spyOn(client, 'sendSession');
+
+    startRequestSession(client, { requestIsolationScope: new Scope() })();
+
+    vi.advanceTimersByTime(59_999);
+    expect(sendSessionSpy).not.toHaveBeenCalled();
+    vi.advanceTimersByTime(1);
+    expect(sendSessionSpy).toHaveBeenCalledTimes(1);
+  });
+});
+
+describe('recordRequestSession()', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('March 19, 1999 06:12:34 UTC'));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('counts the session when the response emits close', () => {
+    const client = createTestClient();
+    const sendSessionSpy = vi.spyOn(client, 'sendSession');
+    const response = Object.assign(new EventEmitter(), { statusCode: 200, headers: {} });
+
+    recordRequestSession(client, { requestIsolationScope: new Scope(), response });
+    vi.runAllTimers();
+    expect(sendSessionSpy).not.toHaveBeenCalled();
+
+    response.emit('close');
+    vi.runAllTimers();
+
+    expect(sendSessionSpy).toHaveBeenCalledWith({
+      aggregates: [{ crashed: 0, errored: 0, exited: 1, started: '1999-03-19T06:12:00.000Z' }],
+    });
+  });
+});
@@ -61,6 +61,23 @@ export type DenoServeIntegrationOptions = {
    */
   onSpanEnd?: (span: Span, request: Request, response: Response) => void;
 
+  /**
+   * Whether the integration should create [Sessions](https://docs.sentry.io/product/releases/health/#sessions) for
+   * incoming requests to track the health and crash-free rate of your releases in Sentry.
+   *
+   * For a streamed response, the session ends when the stream finishes.
+   *
+   * @default `true`
+   */
+  sessions?: boolean;
+
+  /**
+   * Number of milliseconds until sessions are flushed as a session aggregate.
+   *
+   * @default `60000` (60s)
+   */
+  sessionFlushingDelayMS?: number;
+
   /**
    * Do not capture spans for incoming `Deno.serve` requests with the given status codes.
    * By default, some 3xx and 4xx status codes are dropped (see @default).
@@ -149,6 +166,8 @@ const _denoServeIntegration = ((options: DenoServeIntegrationOptions = {}) => {
     spans: options.spans,
     onSpanCreated: options.onSpanCreated,
     onSpanEnd: options.onSpanEnd,
+    sessions: options.sessions ?? true,
+    sessionFlushingDelayMS: options.sessionFlushingDelayMS,
     processEvent(event: Event): Event | null {
       // Gated on this integration's own span origin so it does not filter `node:http`
       // transactions, which `denoHttpIntegration` owns via its own `ignoreStatusCodes`.
 
@@ -2,17 +2,17 @@ import type { Span } from '@sentry/core';
 import { classifyResponseStreaming } from '@sentry/core/server';
 
 /**
- * Tee a stream, and end the provided span when the stream ends.
+ * Tee a stream, and end the provided span (if any) when the stream ends.
  * Returns the other side of the tee, which can be used to send the
  * response to a client.
  *
  * `onEnd` runs right before the span ends.
  */
-export async function streamResponse(span: Span, res: Response, onEnd?: () => void): Promise<Response> {
+export async function streamResponse(span: Span | undefined, res: Response, onEnd?: () => void): Promise<Response> {
   const classification = classifyResponseStreaming(res);
   const endSpan = (): void => {
     onEnd?.();
-    span.end();
+    span?.end();
   };
 
   // not streaming, just end the span and return the response
 
@@ -25,7 +25,7 @@ import {
   winterCGRequestToRequestData,
   withIsolationScope,
 } from '@sentry/core';
-import { getClientIPAddress, isStaticAssetRequest } from '@sentry/core/server';
+import { getClientIPAddress, isStaticAssetRequest, startRequestSession } from '@sentry/core/server';
 import type { DenoServeIntegrationOptions } from './integrations/deno-serve';
 import { streamResponse } from './utils/streaming';
 
@@ -95,17 +95,25 @@ export const wrapDenoRequestHandler = <Addr extends Deno.Addr = Deno.Addr>(
     }
     isolationScope.setClient(client);
 
+    const integration = client.getIntegrationByName<Integration & DenoServeIntegrationOptions>('DenoServe');
+    const endSession = integration?.sessions
+      ? startRequestSession(client, {
+          requestIsolationScope: isolationScope,
+          sessionFlushingDelayMS: integration.sessionFlushingDelayMS,
+        })
+      : undefined;
+
     if (request.method === 'OPTIONS' || request.method === 'HEAD') {
       try {
         return await handler();
       } catch (e) {
         captureServeError(e);
         throw e;
+      } finally {
+        endSession?.();
       }
     }
 
-    const integration = client.getIntegrationByName<Integration & DenoServeIntegrationOptions>('DenoServe');
-
     const urlObject = parseStringToURLObject(request.url);
     const [rawName, attributes] = getHttpSpanDetailsFromUrlObject(
       urlObject,
@@ -174,16 +182,18 @@ export const wrapDenoRequestHandler = <Addr extends Deno.Addr = Deno.Addr>(
       },
       async () => {
         if (!createSpan) {
+          let res: Response;
           try {
-            const res = await handler();
+            res = await handler();
             isolationScope.setContext('response', {
               status_code: res.status,
             });
-            return res;
           } catch (e) {
             captureServeError(e);
+            endSession?.();
             throw e;
           }
+          return endSession ? streamResponse(undefined, res, endSession) : res;
         }
 
         return startSpanManual({ name, attributes }, async span => {
@@ -205,14 +215,16 @@ export const wrapDenoRequestHandler = <Addr extends Deno.Addr = Deno.Addr>(
           } catch (e) {
             span.end();
             captureServeError(e);
+            endSession?.();
             throw e;
           }
 
-          return streamResponse(
-            span,
-            res,
-            onSpanEnd && (() => callHook('onSpanEnd', () => onSpanEnd(span, request, res))),
-          );
+          return streamResponse(span, res, () => {
+            if (onSpanEnd) {
+              callHook('onSpanEnd', () => onSpanEnd(span, request, res));
+            }
+            endSession?.();
+          });
         });
       },
     );