diff --git a/.github/workflows/server-compatibility.yml b/.github/workflows/server-compatibility.yml
new file mode 100644
index 0000000..487c5ec
--- /dev/null
+++ b/.github/workflows/server-compatibility.yml
@@ -0,0 +1,105 @@
+# SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+name: Server compatibility
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+concurrency:
+  group: server-compatibility-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  compatibility:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+
+    steps:
+      - name: Checkout client
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+
+      - name: Checkout Nextcloud
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+          repository: nextcloud/server
+          ref: stable35
+          path: build/nextcloud
+          submodules: true
+
+      - name: Checkout Usage Statistics Server
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+          repository: LibreCodeCoop/usage_statistics_server
+          ref: main
+          path: build/nextcloud/apps/usage_statistics_server
+
+      - name: Set up PHP
+        uses: shivammathur/setup-php@f3e473d116dcccaddc5834248c87452386958240 # v2.37.2
+        with:
+          php-version: '8.3'
+          extensions: bz2, ctype, curl, dom, fileinfo, gd, iconv, intl, json, libxml, mbstring, openssl, pcntl, posix, session, simplexml, sockets, sqlite, pdo_sqlite, xmlreader, xmlwriter, zip, zlib
+          coverage: none
+          ini-file: development
+          ini-values: disable_functions=
+
+      - name: Install server dependencies
+        working-directory: build/nextcloud/apps/usage_statistics_server
+        run: |
+          composer remove nextcloud/ocp --dev --no-scripts
+          composer install --no-dev --no-scripts --prefer-dist --no-progress
+
+      - name: Install compatibility test dependencies
+        working-directory: tests/integration
+        run: composer install --prefer-dist --no-progress
+
+      - name: Set up Nextcloud
+        working-directory: build/nextcloud
+        run: |
+          mkdir data
+          ./occ maintenance:install \
+            --verbose \
+            --database=sqlite \
+            --database-name=nextcloud \
+            --admin-user admin \
+            --admin-pass admin
+          ./occ app:enable --force usage_statistics_server
+          ./occ config:system:set auth.bruteforce.protection.enabled --value false --type boolean
+          ./occ config:system:set ratelimit.protection.enabled --value false --type boolean
+          ./occ config:system:set debug --value true --type boolean
+
+      - name: Run client/server compatibility test
+        working-directory: tests/integration
+        env:
+          BEHAT_ROOT_DIR: ../../build/nextcloud
+          BEHAT_RUN_AS: runner
+          BEHAT_VERBOSE: ${{ runner.debug }}
+        run: |
+          mkdir -p output
+          set -o pipefail
+          composer run behat 2>&1 | tee output/compatibility.log
+
+      - name: Upload Behat results
+        if: always()
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: server-compatibility-results
+          path: |
+            tests/integration/output/
+            build/nextcloud/data/nextcloud.log
+          if-no-files-found: ignore
+          retention-days: 30
+
+      - name: Print Nextcloud logs
+        if: always()
+        run: cat build/nextcloud/data/nextcloud.log 2>/dev/null || true
diff --git a/REUSE.toml b/REUSE.toml
index 8f4b9e0..7be64cb 100644
--- a/REUSE.toml
+++ b/REUSE.toml
@@ -15,7 +15,8 @@ path = [
     "phpunit.xml.dist",
     "phpmd.xml",
     "psalm.xml",
-    "vendor-bin/**/composer.json"
+    "vendor-bin/**/composer.json",
+    "tests/integration/composer.json"
 ]
 precedence = "aggregate"
 SPDX-FileCopyrightText = "2026 LibreCode coop and contributors"
diff --git a/tests/integration/composer.json b/tests/integration/composer.json
new file mode 100644
index 0000000..d9b402c
--- /dev/null
+++ b/tests/integration/composer.json
@@ -0,0 +1,31 @@
+{
+  "repositories": [
+    {
+      "type": "path",
+      "url": "../..",
+      "options": {
+        "symlink": true
+      }
+    }
+  ],
+  "require": {
+    "behat/behat": "3.32.0",
+    "guzzlehttp/guzzle": "7.15.3",
+    "jarnaiz/behat-junit-formatter": "1.3.2",
+    "librecodecoop/usage-statistics-client": "@dev",
+    "libresign/nextcloud-behat": "1.6.0",
+    "php-http/guzzle7-adapter": "1.1.0",
+    "php-http/message": "1.16.2"
+  },
+  "scripts": {
+    "behat": "@php -d error_reporting=24575 vendor/bin/behat -f junit -f pretty --colors"
+  },
+  "config": {
+    "allow-plugins": {
+      "php-http/discovery": true
+    },
+    "platform": {
+      "php": "8.3"
+    }
+  }
+}
diff --git a/tests/integration/config/behat.yml b/tests/integration/config/behat.yml
new file mode 100644
index 0000000..c1c32e3
--- /dev/null
+++ b/tests/integration/config/behat.yml
@@ -0,0 +1,19 @@
+# SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+default:
+  autoload:
+    '': '%paths.base%/../features/bootstrap'
+  suites:
+    default:
+      contexts:
+        - FeatureContext
+      paths:
+        - '%paths.base%/../features'
+
+  extensions:
+    PhpBuiltin\Server:
+      workers: 2
+    jarnaiz\JUnitFormatter\JUnitFormatterExtension:
+      filename: report.xml
+      outputDir: '%paths.base%/../output/'
diff --git a/tests/integration/features/bootstrap/FeatureContext.php b/tests/integration/features/bootstrap/FeatureContext.php
new file mode 100644
index 0000000..e0450f0
--- /dev/null
+++ b/tests/integration/features/bootstrap/FeatureContext.php
@@ -0,0 +1,99 @@
+<?php
+
+/**
+ * SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+declare(strict_types=1);
+
+use Behat\Step\Given;
+use Behat\Step\When;
+use GuzzleHttp\Client as HttpClient;
+use LibreCode\UsageStatistics\Client;
+use LibreCode\UsageStatistics\ConsentState;
+use LibreCode\UsageStatistics\Endpoint;
+use LibreCode\UsageStatistics\InstallationId;
+use LibreCode\UsageStatistics\Metric;
+use LibreCode\UsageStatistics\Report;
+use LibreCode\UsageStatistics\ReportingPeriod;
+use LibreCode\UsageStatistics\SubmissionResult;
+use LibreCode\UsageStatistics\Transport\Response;
+use LibreCode\UsageStatistics\Transport\TransportInterface;
+use Libresign\NextcloudBehat\NextcloudApiContext;
+
+final class FeatureContext extends NextcloudApiContext {
+	#[Given('as anonymous user')]
+	public function asAnonymousUser(): void {
+		$this->setCurrentUser('');
+	}
+
+	#[When('the usage statistics client submits the compatibility report')]
+	public function submitCompatibilityReport(): void {
+		$report = new Report(
+			application: 'client_server_e2e',
+			installationId: (string)InstallationId::derive('client_server_e2e', 'integration-installation'),
+			schemaVersion: 1,
+			period: new ReportingPeriod(
+				new \DateTimeImmutable('2026-09-01T00:00:00Z'),
+				new \DateTimeImmutable('2026-10-01T00:00:00Z'),
+			),
+			metrics: [
+				Metric::string('environment', 'version', '1.2.3'),
+				Metric::integer('usage', 'requests_completed', 17),
+			],
+		);
+
+		$transport = new class($this->baseUrl) implements TransportInterface {
+			public function __construct(
+				private readonly string $baseUrl,
+			) {
+			}
+
+			public function request(
+				string $method,
+				string $url,
+				array $headers,
+				string $body,
+				float $timeoutSeconds,
+			): Response {
+				$path = parse_url($url, PHP_URL_PATH);
+				if (!is_string($path) || $path === '') {
+					throw new \RuntimeException('Compatibility endpoint path is invalid.');
+				}
+
+				$http = new HttpClient(['http_errors' => false]);
+				$response = $http->request(
+					$method,
+					rtrim($this->baseUrl, '/') . $path,
+					[
+						'headers' => $headers,
+						'body' => $body,
+						'timeout' => $timeoutSeconds,
+					],
+				);
+
+				$responseHeaders = [];
+				foreach ($response->getHeaders() as $name => $values) {
+					$responseHeaders[$name] = implode(', ', $values);
+				}
+
+				return new Response(
+					$response->getStatusCode(),
+					(string)$response->getBody(),
+					$responseHeaders,
+				);
+			}
+		};
+
+		$client = new Client(
+			$transport,
+			new Endpoint('https://usage-statistics.invalid/index.php/apps/usage_statistics_server/api/v1/reports'),
+		);
+
+		$result = $client->submit($report, ConsentState::Enabled);
+		if ($result !== SubmissionResult::Accepted) {
+			throw new \RuntimeException('Compatibility report was not accepted.');
+		}
+	}
+}
diff --git a/tests/integration/features/client_server_compatibility.feature b/tests/integration/features/client_server_compatibility.feature
new file mode 100644
index 0000000..198e71b
--- /dev/null
+++ b/tests/integration/features/client_server_compatibility.feature
@@ -0,0 +1,30 @@
+# SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+Feature: Usage Statistics Protocol v1 client/server compatibility
+
+  Scenario: the real client submits a report that the server stores and aggregates
+    Given as user "admin"
+    When sending "post" to ocs "/apps/usage_statistics_server/api/v1/admin/schemas"
+      | application   | client_server_e2e |
+      | schemaVersion | 1 |
+      | metrics       | [{"category":"environment","key":"version","type":"string","kind":"snapshot","aggregation":"distribution","description":"Application version","required":true},{"category":"usage","key":"requests_completed","type":"integer","kind":"period","aggregation":"numerical","description":"Completed requests","required":true}] |
+    Then the response should have a status code 201
+
+    When the usage statistics client submits the compatibility report
+
+    Given as user "admin"
+    When sending "get" to ocs "/apps/usage_statistics_server/api/v1/admin/applications/client_server_e2e/metrics/environment/version/distribution"
+    Then the response should have a status code 200
+    And the response should be a JSON array with the following mandatory values
+      | key                             | value |
+      | (jq).ocs.data.values[0].value   | 1.2.3 |
+      | (jq).ocs.data.values[0].count   | 1     |
+
+    When sending "get" to ocs "/apps/usage_statistics_server/api/v1/admin/applications/client_server_e2e/metrics/usage/requests_completed/numerical"
+    Then the response should have a status code 200
+    And the response should be a JSON array with the following mandatory values
+      | key                               | value |
+      | (jq).ocs.data.statistics.count    | 1     |
+      | (jq).ocs.data.statistics.average  | 17    |
+      | (jq).ocs.data.statistics.total    | 17    |