diff --git a/.github/workflows/pythonpackage.yml b/.github/workflows/pythonpackage.yml
index 65950e72..5a06a31d 100644
--- a/.github/workflows/pythonpackage.yml
+++ b/.github/workflows/pythonpackage.yml
@@ -8,7 +8,7 @@ jobs:
     strategy:
       max-parallel: 4
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.7, 3.8, 3.9]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}
@@ -28,10 +28,10 @@ jobs:
     if: startsWith(github.event.ref, 'refs/tags')
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.8
+    - name: Set up Python 3.9
       uses: actions/setup-python@v1
       with:
-        python-version: 3.8
+        python-version: 3.9
     - name: Build a binary wheel and a source tarball
       run: |
         pip install wheel
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 6f3b4db5..11e3dc30 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -5,7 +5,7 @@ repos:
   rev: stable
   hooks:
   - id: black
-    language_version: python3.6
+    language_version: python3.7
 - repo: git://github.com/pre-commit/pre-commit-hooks
   rev: v2.2.3
   hooks:
diff --git a/pyproject.toml b/pyproject.toml
index e12ececb..493d87cf 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -3,7 +3,7 @@ requires = ["setuptools", "wheel"]
 
 [tool.black]
 line-length = 79
-target-version = ['py36']
+target-version = ['py37']
 include = '\.pyi?$'
 exclude = '''
 (
diff --git a/setup.cfg b/setup.cfg
index c9701fa8..3af83a66 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -13,7 +13,7 @@ long-description-content-type = text/markdown; charset=UTF-8; variant=GFM
 url = https://github.com/qase-tms/qase-python
 platforms = any
 classifiers =
-    Development Status :: 4 - Beta
+    Development Status :: 5 - Production/Stable
     Programming Language :: Python
 
 [options]
@@ -27,10 +27,10 @@ package_dir =
 setup_requires = pyscaffold>=3.2a0,<3.3a0
 # Add here dependencies of your project (semicolon/line-separated), e.g.
 install_requires =
-    python-apitist>=0.5.1
+    apitist>=3.0.0
     attrs>=19.3.0
     cattrs>=1.0.0
-python_requires = >=3.6
+python_requires = >=3.7
 
 [options.packages.find]
 where = src
diff --git a/src/qaseio/client/services/plans.py b/src/qaseio/client/services/plans.py
index bbf6ddbd..7f0a8b29 100644
--- a/src/qaseio/client/services/plans.py
+++ b/src/qaseio/client/services/plans.py
@@ -12,7 +12,10 @@
 
 class Plans(BaseService):
     def get_all(
-        self, code: str, limit=None, offset=None,
+        self,
+        code: str,
+        limit=None,
+        offset=None,
     ):
         query = {"limit": limit, "offset": offset}
         return self.vr(
diff --git a/src/qaseio/client/services/shared_steps.py b/src/qaseio/client/services/shared_steps.py
index a0b848e8..b067b6bb 100644
--- a/src/qaseio/client/services/shared_steps.py
+++ b/src/qaseio/client/services/shared_steps.py
@@ -40,7 +40,10 @@ def create(self, code: str, data: SharedStepCreate):
         )
 
     def update(
-        self, code: str, shared_step_hash: str, data: SharedStepUpdate,
+        self,
+        code: str,
+        shared_step_hash: str,
+        data: SharedStepUpdate,
     ):
         return self.vr(
             self.s.patch(
diff --git a/src/qaseio/client/services/users.py b/src/qaseio/client/services/users.py
index e88bb2fe..d435f99f 100644
--- a/src/qaseio/client/services/users.py
+++ b/src/qaseio/client/services/users.py
@@ -15,7 +15,8 @@ def get_all(self, limit=None, offset=None):
 
     def get(self, user_id: Union[str, int]):
         return self.vr(
-            self.s.get(self.path("user/{}".format(user_id))), to_type=UserInfo,
+            self.s.get(self.path("user/{}".format(user_id))),
+            to_type=UserInfo,
         )
 
     def exists(self, code: str):
diff --git a/tests/qaseio/services/test_defects.py b/tests/qaseio/services/test_defects.py
index 089cbdf7..d16d3c52 100644
--- a/tests/qaseio/services/test_defects.py
+++ b/tests/qaseio/services/test_defects.py
@@ -20,7 +20,11 @@
         ((None, 30), "?offset=30"),
         ((10, None), "?limit=10"),
         (
-            (10, None, DefectFilters(status=DefectStatus.OPEN),),
+            (
+                10,
+                None,
+                DefectFilters(status=DefectStatus.OPEN),
+            ),
             "?limit=10&filters%5Bstatus%5D=open",
         ),
     ],
diff --git a/tests/qaseio/services/test_milestones.py b/tests/qaseio/services/test_milestones.py
index 8ba56bfe..df74b148 100644
--- a/tests/qaseio/services/test_milestones.py
+++ b/tests/qaseio/services/test_milestones.py
@@ -23,7 +23,11 @@
         ((None, 30), "?offset=30"),
         ((10, None), "?limit=10"),
         (
-            (10, None, MilestoneFilters(search="123"),),
+            (
+                10,
+                None,
+                MilestoneFilters(search="123"),
+            ),
             "?limit=10&filters%5Bsearch%5D=123",
         ),
     ],
diff --git a/tests/qaseio/services/test_shared_steps.py b/tests/qaseio/services/test_shared_steps.py
index 04c564fe..646915c8 100644
--- a/tests/qaseio/services/test_shared_steps.py
+++ b/tests/qaseio/services/test_shared_steps.py
@@ -23,7 +23,11 @@
         ((None, 30), "?offset=30"),
         ((10, None), "?limit=10"),
         (
-            (10, None, SharedStepFilters(search="123"),),
+            (
+                10,
+                None,
+                SharedStepFilters(search="123"),
+            ),
             "?limit=10&filters%5Bsearch%5D=123",
         ),
     ],
diff --git a/tests/qaseio/services/test_suites.py b/tests/qaseio/services/test_suites.py
index 81111f28..61294374 100644
--- a/tests/qaseio/services/test_suites.py
+++ b/tests/qaseio/services/test_suites.py
@@ -23,7 +23,11 @@
         ((None, 30), "?offset=30"),
         ((10, None), "?limit=10"),
         (
-            (10, None, TestSuiteFilters(search="123"),),
+            (
+                10,
+                None,
+                TestSuiteFilters(search="123"),
+            ),
             "?limit=10&filters%5Bsearch%5D=123",
         ),
     ],
diff --git a/tests/qaseio/test_models.py b/tests/qaseio/test_models.py
index a681fab6..1d055727 100644
--- a/tests/qaseio/test_models.py
+++ b/tests/qaseio/test_models.py
@@ -78,14 +78,16 @@ def test_invalid_project_creation(data):
 
 
 @pytest.mark.parametrize(
-    "data", [("", [1]), ("a" * 65, [13, 14, 15], "a" * 65, 123)],
+    "data",
+    [("", [1]), ("a" * 65, [13, 14, 15], "a" * 65, 123)],
 )
 def test_valid_test_run_creation(data):
     TestRunCreate(*data)
 
 
 @pytest.mark.parametrize(
-    "data", [("a", []), ("a", 123)],
+    "data",
+    [("a", []), ("a", 123)],
 )
 def test_invalid_test_run_creation(data):
     with pytest.raises(ValueError):
@@ -93,14 +95,16 @@ def test_invalid_test_run_creation(data):
 
 
 @pytest.mark.parametrize(
-    "data", [("", [1]), ("a" * 65, [13, 14, 15], "a" * 65)],
+    "data",
+    [("", [1]), ("a" * 65, [13, 14, 15], "a" * 65)],
 )
 def test_valid_test_plan_creation(data):
     TestPlanCreate(*data)
 
 
 @pytest.mark.parametrize(
-    "data", [("a", []), ("a", 123)],
+    "data",
+    [("a", []), ("a", 123)],
 )
 def test_invalid_test_plan_creation(data):
     with pytest.raises(ValueError):