diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index a5abb77..8ee7cd8 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -33,6 +33,7 @@ jobs:
           - "3.10"
           - "3.11"
           - "3.12"
+          - "3.13"
     steps:
       - name: Checkout
         uses: actions/checkout@v4
diff --git a/CHANGELOG.md b/CHANGELOG.md
index e5dcfd9..f7fda26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ Format basiert auf [Keep a Changelog](https://keepachangelog.com/de/1.1.0/).
 
 ## [Unreleased]
 
+### Behoben / Fixed (2026-11-01)
+- **PEP 639 Metadaten-Standardisierung & CI-Matrix-Härtung (Pfad A Repository-Hygiene):**
+  - **PEP 639 Lizenz-Spezifikation (`pyproject.toml`):** `license = { text = "MIT" }` auf standardkonformen SPDX-String `license = "MIT"` migriert; veralteten Classifier `"License :: OSI Approved :: MIT License"` aus `classifiers` entfernt, um strikte Build-Validierungsfehler (`ValueError: invalid pyproject.toml config: project.license`) in modernen Setuptools-Versionen (>=82.0) fail-closed zu beheben.
+  - **CI-Matrix-Härtung (`.github/workflows/tests.yml`):** Test-Matrix um Python 3.13 (`"3.13"`) erweitert zur Sicherung der Vorwärtskompatibilität über die gesamte Python 3.10–3.13 Matrix unter Ubuntu-Runnern.
+  - **Automatisierte Vertragstest-Erweiterung (`tests/test_metadata.py`):** Neuer hermetischer Vertragstest `test_pep_639_license_specification` verankert die PEP-639-Konformität und das Classifier-Verbot; `test_ci_workflow_integrity` um Python 3.13 Matrix-Prüfung ergänzt.
+
 ### Behoben / Fixed (2026-10-31)
 - **Windows-atomare Dateisystem-Resilienz & Translation CLI CWD-Unabhängigkeit (Software-Bugsearch / Bugsweep):**
   - **Windows ReadOnly-Overwrite & WinError 5/32 Resilienz (`prosync_utils.py`):** `atomic_write_text` und `atomic_write_json` heben unter Windows vorübergehend den Schreibschutz auf (`stat.S_IWRITE`), wenn die Zieldatei schreibgeschützt existiert, wodurch `PermissionError: [WinError 5] Zugriff verweigert` beim atomaren `os.replace` verhindert wird (inkl. Wiederherstellung des ursprünglichen Dateimodus im Fehlerfall).
diff --git a/pyproject.toml b/pyproject.toml
index 4436a67..8698521 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,7 +8,7 @@ version = "3.2.0"
 description = "Intelligent local backup synchronization desktop app with automated SQLite WAL database protection"
 readme = "README.md"
 requires-python = ">=3.10"
-license = { text = "MIT" }
+license = "MIT"
 license-files = ["LICENSE", "NOTICE", "CONTRIBUTING.md", "THIRD_PARTY_LICENSES.md", "THIRD_PARTY_LICENSES.txt"]
 authors = [
     { name = "file-bricks Team", email = "support@lukasgeiger.com" }
@@ -39,7 +39,6 @@ classifiers = [
     "Development Status :: 5 - Production/Stable",
     "Environment :: Win32 (MS Windows)",
     "Intended Audience :: End Users/Desktop",
-    "License :: OSI Approved :: MIT License",
     "Operating System :: Microsoft :: Windows",
     "Operating System :: POSIX :: Linux",
     "Operating System :: MacOS",
diff --git a/tests/test_metadata.py b/tests/test_metadata.py
index 245ca97..effd612 100644
--- a/tests/test_metadata.py
+++ b/tests/test_metadata.py
@@ -119,6 +119,18 @@ def test_pyproject_pep621_metadata() -> None:
     assert "norecursedirs =" in content, "norecursedirs missing in pyproject.toml"
 
 
+def test_pep_639_license_specification() -> None:
+    """Verify pyproject.toml defines license as a valid PEP 639 SPDX string without deprecated license classifiers."""
+    pyproject_file = ROOT / "pyproject.toml"
+    assert pyproject_file.is_file(), "pyproject.toml must exist"
+    content = pyproject_file.read_text(encoding="utf-8")
+
+    assert 'license = "MIT"' in content, "pyproject.toml must declare license as SPDX string 'license = \"MIT\"'"
+    assert "License :: OSI Approved ::" not in content, (
+        "pyproject.toml must not include 'License :: OSI Approved :: ...' in classifiers when PEP 639 SPDX string license is used"
+    )
+
+
 def test_ci_workflow_integrity() -> None:
     """Verify GitHub Actions CI workflows exist and have test coverage."""
     workflow_dir = ROOT / ".github" / "workflows"
@@ -128,6 +140,7 @@ def test_ci_workflow_integrity() -> None:
     tests_yml = (workflow_dir / "tests.yml").read_text(encoding="utf-8")
     assert "python run_tests.py" in tests_yml
     assert "python -m pytest -ra -v" in tests_yml
+    assert '"3.13"' in tests_yml, "Python 3.13 matrix entry missing in tests.yml"
 
 
 def test_ci_concurrency_and_timeout_guardrails() -> None: