diff --git a/packages/google_cloud_storage/_dev/deploy/docker/docker-compose.yml b/packages/google_cloud_storage/_dev/deploy/docker/docker-compose.yml
index eb4f52c7cd9..87f214f7ce7 100644
--- a/packages/google_cloud_storage/_dev/deploy/docker/docker-compose.yml
+++ b/packages/google_cloud_storage/_dev/deploy/docker/docker-compose.yml
@@ -1,9 +1,16 @@
 version: '2.3'
 services:
-  google-cloud-storage-emulator:
-    image: fsouza/fake-gcs-server:latest
-    command: -host=0.0.0.0 -public-host=elastic-package-service_google-cloud-storage-emulator_1 -port=4443 -scheme=http
+  gcs-mock-service:
+    image: golang:1.24.7-alpine
+    working_dir: /app
     volumes:
-      - ./sample_logs:/data
+      - ./gcs-mock-service:/app
+      - ./files/manifest.yml:/files/manifest.yml:ro
+      - ./sample_logs/:/data:ro
     ports:
-      - 4443/tcp
+      - "4443/tcp"
+    healthcheck:
+      test: "wget --no-verbose --tries=1 --spider http://localhost:4443/health || exit 1"
+      interval: 10s
+      timeout: 5s
+    command: go run main.go -manifest /files/manifest.yml
diff --git a/packages/google_cloud_storage/_dev/deploy/docker/files/manifest.yml b/packages/google_cloud_storage/_dev/deploy/docker/files/manifest.yml
new file mode 100644
index 00000000000..61e12fd5342
--- /dev/null
+++ b/packages/google_cloud_storage/_dev/deploy/docker/files/manifest.yml
@@ -0,0 +1,5 @@
+buckets:
+  testbucket:
+    files:
+      - path: /data/testbucket/testdata.log
+        content-type: application/x-ndjson
diff --git a/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/go.mod b/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/go.mod
new file mode 100644
index 00000000000..df08767f7e8
--- /dev/null
+++ b/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/go.mod
@@ -0,0 +1,5 @@
+module gcs-mock-service
+
+go 1.24.7
+
+require gopkg.in/yaml.v3 v3.0.1
diff --git a/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/go.sum b/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/go.sum
new file mode 100644
index 00000000000..a62c313c5b0
--- /dev/null
+++ b/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/go.sum
@@ -0,0 +1,4 @@
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/main.go b/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/main.go
new file mode 100644
index 00000000000..391e75c7efe
--- /dev/null
+++ b/packages/google_cloud_storage/_dev/deploy/docker/gcs-mock-service/main.go
@@ -0,0 +1,297 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+func main() {
+	host := flag.String("host", "0.0.0.0", "host to listen on")
+	port := flag.String("port", "4443", "port to listen on")
+	manifest := flag.String("manifest", "", "path to YAML manifest file for preloading buckets and objects")
+	flag.Parse()
+
+	addr := fmt.Sprintf("%s:%s", *host, *port)
+
+	fmt.Printf("Starting mock GCS server on http://%s\n", addr)
+	if *manifest != "" {
+		m, err := readManifest(*manifest)
+		if err != nil {
+			log.Fatalf("error reading manifest: %v", err)
+		}
+		if err := processManifest(m); err != nil {
+			log.Fatalf("error processing manifest: %v", err)
+		}
+	} else {
+		fmt.Println("Store is empty. Create buckets and objects via API calls.")
+	}
+
+	// setup HTTP handlers
+	mux := http.NewServeMux()
+	// health check
+	mux.HandleFunc("/health", healthHandler)
+	// standard gcs api calls
+	mux.HandleFunc("GET /storage/v1/b/{bucket}/o", handleListObjects)
+	mux.HandleFunc("GET /storage/v1/b/{bucket}/o/{object...}", handleGetObject)
+	mux.HandleFunc("POST /storage/v1/b", handleCreateBucket)
+	mux.HandleFunc("POST /upload/storage/v1/b/{bucket}/o", handleUploadObject)
+	mux.HandleFunc("POST /upload/storage/v1/b/{bucket}/o/{object...}", handleUploadObject)
+	// direct path-style gcs sdk calls
+	mux.HandleFunc("GET /{bucket}/o/{object...}", handleGetObject)
+	mux.HandleFunc("GET /{bucket}/{object...}", handleGetObject)
+	// debug: log all requests
+	loggedMux := loggingMiddleware(mux)
+
+	if err := http.ListenAndServe(addr, loggedMux); err != nil {
+		log.Fatalf("failed to start server: %v", err)
+	}
+}
+
+// loggingMiddleware logs incoming HTTP requests.
+func loggingMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Printf("%s %s\n", r.Method, r.URL.Path)
+		next.ServeHTTP(w, r)
+	})
+}
+
+// readManifest reads and parses the YAML manifest file.
+func readManifest(path string) (*Manifest, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read manifest: %w", err)
+	}
+
+	var manifest Manifest
+	if err := yaml.Unmarshal(data, &manifest); err != nil {
+		return nil, fmt.Errorf("failed to parse manifest: %w", err)
+	}
+
+	return &manifest, nil
+}
+
+// processManifest creates buckets and uploads objects as specified in the manifest.
+func processManifest(manifest *Manifest) error {
+	for bucketName, bucket := range manifest.Buckets {
+		for _, file := range bucket.Files {
+			fmt.Printf("preloading data for bucket: %s | path: %s | content-type: %s...\n",
+				bucketName, file.Path, file.ContentType)
+
+			if err := createBucket(bucketName); err != nil {
+				return fmt.Errorf("failed to create bucket '%s': %w", bucketName, err)
+			}
+			data, err := os.ReadFile(file.Path)
+			if err != nil {
+				return fmt.Errorf("failed to read bucket data file '%s': %w", file.Path, err)
+			}
+			pathParts := strings.Split(file.Path, "/")
+			if _, err := uploadObject(bucketName, pathParts[len(pathParts)-1], data, file.ContentType); err != nil {
+				return fmt.Errorf("failed to create object '%s' in bucket '%s': %w", file.Path, bucketName, err)
+			}
+		}
+	}
+	return nil
+}
+
+// healthHandler responds with a simple "OK" message for health checks.
+func healthHandler(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(http.StatusOK)
+	fmt.Fprint(w, "OK")
+}
+
+// handleListObjects lists all objects in the specified bucket.
+func handleListObjects(w http.ResponseWriter, r *http.Request) {
+	bucketName := r.PathValue("bucket")
+
+	if bucket, ok := inMemoryStore[bucketName]; ok {
+		response := GCSListResponse{
+			Kind:  "storage#objects",
+			Items: []GCSObject{},
+		}
+		for name, object := range bucket {
+			item := GCSObject{
+				Kind:        "storage#object",
+				Name:        name,
+				Bucket:      bucketName,
+				Size:        strconv.Itoa(len(object.Data)),
+				ContentType: object.ContentType,
+			}
+			response.Items = append(response.Items, item)
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(response)
+		return
+	}
+	http.Error(w, "not found", http.StatusNotFound)
+}
+
+// handleGetObject retrieves a specific object from a bucket.
+func handleGetObject(w http.ResponseWriter, r *http.Request) {
+	bucketName := r.PathValue("bucket")
+	objectName := r.PathValue("object")
+
+	if bucketName == "" || objectName == "" {
+		http.Error(w, "not found: invalid URL format", http.StatusNotFound)
+		return
+	}
+
+	if bucket, ok := inMemoryStore[bucketName]; ok {
+		if object, ok := bucket[objectName]; ok {
+			w.Header().Set("Content-Type", object.ContentType)
+			w.Write(object.Data)
+			return
+		}
+	}
+	http.Error(w, "not found", http.StatusNotFound)
+}
+
+// handleCreateBucket creates a new bucket.
+func handleCreateBucket(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.NotFound(w, r)
+		return
+	}
+
+	var bucketInfo struct {
+		Name string `json:"name"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&bucketInfo); err != nil {
+		http.Error(w, "invalid JSON body", http.StatusBadRequest)
+		return
+	}
+	if bucketInfo.Name == "" {
+		http.Error(w, "bucket name is required", http.StatusBadRequest)
+		return
+	}
+
+	if err := createBucket(bucketInfo.Name); err != nil {
+		http.Error(w, err.Error(), http.StatusConflict)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+	json.NewEncoder(w).Encode(bucketInfo)
+}
+
+// handleUploadObject uploads an object to a specified bucket.
+func handleUploadObject(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.NotFound(w, r)
+		return
+	}
+
+	bucketName := r.PathValue("bucket")
+	objectName := r.URL.Query().Get("name")
+	if objectName == "" {
+		objectName = r.PathValue("object")
+	}
+
+	if bucketName == "" || objectName == "" {
+		http.Error(w, "missing bucket or object name", http.StatusBadRequest)
+		return
+	}
+
+	data, err := io.ReadAll(r.Body)
+	if err != nil {
+		http.Error(w, "failed to read request body", http.StatusInternalServerError)
+		return
+	}
+	defer r.Body.Close()
+
+	contentType := r.Header.Get("Content-Type")
+	if contentType == "" {
+		contentType = "application/octet-stream"
+	}
+
+	response, err := uploadObject(bucketName, objectName, data, contentType)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusNotFound)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response)
+}
+
+func createBucket(bucketName string) error {
+	if _, exists := inMemoryStore[bucketName]; exists {
+		return fmt.Errorf("bucket already exists")
+	}
+	inMemoryStore[bucketName] = make(map[string]ObjectData)
+	log.Printf("created bucket: %s", bucketName)
+	return nil
+}
+
+func uploadObject(bucketName, objectName string, data []byte, contentType string) (*GCSObject, error) {
+	if _, ok := inMemoryStore[bucketName]; !ok {
+		return nil, fmt.Errorf("bucket not found")
+	}
+
+	inMemoryStore[bucketName][objectName] = ObjectData{
+		Data:        data,
+		ContentType: contentType,
+	}
+	log.Printf("created object '%s' in bucket '%s' with Content-Type '%s'",
+		objectName, bucketName, contentType)
+
+	return &GCSObject{
+		Kind:        "storage#object",
+		Name:        objectName,
+		Bucket:      bucketName,
+		Size:        strconv.Itoa(len(data)),
+		ContentType: contentType,
+	}, nil
+}
+
+// The in-memory store to hold ObjectData structs.
+var inMemoryStore = make(map[string]map[string]ObjectData)
+
+// ObjectData stores the raw data and its content type.
+type ObjectData struct {
+	Data        []byte
+	ContentType string
+}
+
+// GCSListResponse mimics the structure of a real GCS object list response.
+type GCSListResponse struct {
+	Kind  string      `json:"kind"`
+	Items []GCSObject `json:"items"`
+}
+
+// GCSObject mimics the structure of a GCS object resource with ContentType.
+type GCSObject struct {
+	Kind        string `json:"kind"`
+	Name        string `json:"name"`
+	Bucket      string `json:"bucket"`
+	Size        string `json:"size"`
+	ContentType string `json:"contentType"`
+}
+
+// Manifest represents the top-level structure of the YAML file
+type Manifest struct {
+	Buckets map[string]Bucket `yaml:"buckets"`
+}
+
+// Bucket represents each bucket and its files
+type Bucket struct {
+	Files []File `yaml:"files"`
+}
+
+// File represents each file entry inside a bucket
+type File struct {
+	Path        string `yaml:"path"`
+	ContentType string `yaml:"content-type"`
+}
diff --git a/packages/google_cloud_storage/_dev/test/system/test-default-config.yml b/packages/google_cloud_storage/_dev/test/system/test-default-config.yml
index 6b19c97c611..0411ba73079 100644
--- a/packages/google_cloud_storage/_dev/test/system/test-default-config.yml
+++ b/packages/google_cloud_storage/_dev/test/system/test-default-config.yml
@@ -1,10 +1,15 @@
-service: google-cloud-storage-emulator
+deployer: docker
+service: gcs-mock-service
 input: gcs
 vars:
   project_id: testproject
   alternative_host: "http://{{Hostname}}:{{Port}}"
+  number_of_workers: 1
+  service_account_key: "{\"type\":\"service_account\",\"project_id\":\"testproject\"}"
   data_stream.dataset: google_cloud_storage.gcs
   buckets: |
     - name: testbucket
       poll: true
       poll_interval: 15s
+assert:
+  hit_count: 1
diff --git a/packages/google_cloud_storage/sample_event.json b/packages/google_cloud_storage/sample_event.json
index 37ef5bb15b6..aab1c49ba86 100644
--- a/packages/google_cloud_storage/sample_event.json
+++ b/packages/google_cloud_storage/sample_event.json
@@ -1,36 +1,57 @@
 {
-    "@timestamp": "2024-04-18T11:56:08.098Z",
+    "@timestamp": "2025-12-25T12:18:28.789Z",
     "agent": {
-        "ephemeral_id": "839b31c3-59b9-4418-b825-8f0ba4219502",
-        "id": "80442ebe-168f-468b-82af-30451478d848",
-        "name": "docker-fleet-agent",
+        "ephemeral_id": "b26cd9f8-57d0-4ccc-a116-e599c04ff251",
+        "id": "8f3305a5-3650-4e75-8687-d419445742be",
+        "name": "elastic-agent-63184",
         "type": "filebeat",
-        "version": "8.12.1"
+        "version": "8.13.0"
+    },
+    "cloud": {
+        "provider": "google cloud"
     },
     "data_stream": {
         "dataset": "google_cloud_storage.gcs",
-        "namespace": "ep",
+        "namespace": "30478",
         "type": "logs"
     },
     "ecs": {
-        "version": "8.11.0"
+        "version": "8.0.0"
     },
     "elastic_agent": {
-        "id": "80442ebe-168f-468b-82af-30451478d848",
+        "id": "8f3305a5-3650-4e75-8687-d419445742be",
         "snapshot": false,
-        "version": "8.12.1"
+        "version": "8.13.0"
     },
     "event": {
         "agent_id_status": "verified",
         "dataset": "google_cloud_storage.gcs",
-        "ingested": "2024-04-18T11:56:20Z"
+        "ingested": "2025-12-25T12:18:31Z"
+    },
+    "gcs": {
+        "storage": {
+            "bucket": {
+                "name": "testbucket"
+            },
+            "object": {
+                "content_type": "application/x-ndjson",
+                "json_data": [],
+                "name": "testdata.log"
+            }
+        }
     },
     "input": {
         "type": "gcs"
     },
-    "message": "job with jobId testbucket-testdata.log-worker-0 encountered an error: content-type text/plain; charset=utf-8 not supported",
+    "log": {
+        "file": {
+            "path": "gs://testbucket/testdata.log"
+        },
+        "offset": 0
+    },
+    "message": "{ \"testmessage\": \"success\" }",
     "tags": [
         "forwarded",
         "google_cloud_storage-generic"
     ]
-}
\ No newline at end of file
+}