diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 6f58f303..ed897ccc 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -39,8 +39,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [3.6, 3.7, 3.8, 3.9, "3.10"]
-      fail-fast: false
+        python-version: [3.7, 3.8, 3.9, "3.10"]
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
     steps:
@@ -60,6 +59,7 @@ jobs:
           pip install codecov
 
       - name: Run flake8, pylint, mypy
+        if: matrix.python-version == '3.10'
         run: |
           flake8 cmdstanpy test
           pylint -v cmdstanpy test
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 9c846751..c32c7de3 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -25,7 +25,7 @@ repos:
       - id: mypy
         # Copied from setup.cfg
         exclude: ^test/
-        additional_dependencies: [ numpy >= 1.21 ]
+        additional_dependencies: [ numpy >= 1.22, types-ujson ]
   # local uses the user-installed pylint, this allows dependency checking
   - repo: local
     hooks:
diff --git a/cmdstanpy/cmdstan_args.py b/cmdstanpy/cmdstan_args.py
index b339f7a5..f5553153 100644
--- a/cmdstanpy/cmdstan_args.py
+++ b/cmdstanpy/cmdstan_args.py
@@ -202,10 +202,7 @@ def validate(self, chains: Optional[int]) -> None:
                 if all(isinstance(elem, dict) for elem in self.metric):
                     metric_files: List[str] = []
                     for i, metric in enumerate(self.metric):
-                        assert isinstance(
-                            metric, dict
-                        )  # make the typechecker happy
-                        metric_dict: Dict[str, Any] = metric
+                        metric_dict: Dict[str, Any] = metric  # type: ignore
                         if 'inv_metric' not in metric_dict:
                             raise ValueError(
                                 'Entry "inv_metric" not found in metric dict '
diff --git a/cmdstanpy/stanfit/mcmc.py b/cmdstanpy/stanfit/mcmc.py
index 70259b8d..571e75c9 100644
--- a/cmdstanpy/stanfit/mcmc.py
+++ b/cmdstanpy/stanfit/mcmc.py
@@ -95,9 +95,9 @@ def __init__(
         self._save_warmup = sampler_args.save_warmup
         self._sig_figs = runset._args.sig_figs
         # info from CSV values, instantiated lazily
-        self._metric = np.array(())
-        self._step_size = np.array(())
-        self._draws = np.array(())
+        self._metric: np.ndarray = np.array(())
+        self._step_size: np.ndarray = np.array(())
+        self._draws: np.ndarray = np.array(())
         # info from CSV initial comments and header
         config = self._validate_csv_files()
         self._metadata: InferenceMetadata = InferenceMetadata(config)
@@ -246,7 +246,7 @@ def draws(
 
         if concat_chains:
             return flatten_chains(self._draws[start_idx:, :, :])
-        return self._draws[start_idx:, :, :]  # type: ignore
+        return self._draws[start_idx:, :, :]
 
     def _validate_csv_files(self) -> Dict[str, Any]:
         """
@@ -675,9 +675,7 @@ def stan_variable(
         if len(col_idxs) > 0:
             dims.extend(self._metadata.stan_vars_dims[var])
         # pylint: disable=redundant-keyword-arg
-        return self._draws[draw1:, :, col_idxs].reshape(  # type: ignore
-            dims, order='F'
-        )
+        return self._draws[draw1:, :, col_idxs].reshape(dims, order='F')
 
     def stan_variables(self) -> Dict[str, np.ndarray]:
         """
@@ -748,7 +746,7 @@ def __init__(
             )
         self.runset = runset
         self.mcmc_sample = mcmc_sample
-        self._draws = np.array(())
+        self._draws: np.ndarray = np.array(())
         config = self._validate_csv_files()
         self._metadata = InferenceMetadata(config)
 
@@ -765,7 +763,7 @@ def __repr__(self) -> str:
         )
         return repr
 
-    def _validate_csv_files(self) -> dict:
+    def _validate_csv_files(self) -> Dict[str, Any]:
         """
         Checks that Stan CSV output files for all chains are consistent
         and returns dict containing config and column names.
@@ -910,13 +908,13 @@ def draws(
         if concat_chains:
             return flatten_chains(self._draws[start_idx:, :, :])
         if inc_sample:
-            return np.dstack(  # type: ignore
+            return np.dstack(
                 (
                     np.delete(self.mcmc_sample.draws(), drop_cols, axis=1),
                     self._draws,
                 )
             )[start_idx:, :, :]
-        return self._draws[start_idx:, :, :]  # type: ignore
+        return self._draws[start_idx:, :, :]
 
     def draws_pd(
         self,
@@ -1195,9 +1193,7 @@ def stan_variable(
             if len(col_idxs) > 0:
                 dims.extend(self._metadata.stan_vars_dims[var])
             # pylint: disable=redundant-keyword-arg
-            return self._draws[draw1:, :, col_idxs].reshape(  # type: ignore
-                dims, order='F'
-            )
+            return self._draws[draw1:, :, col_idxs].reshape(dims, order='F')
 
     def stan_variables(self, inc_warmup: bool = False) -> Dict[str, np.ndarray]:
         """
@@ -1229,7 +1225,7 @@ def _assemble_generated_quantities(self) -> None:
         # use numpy loadtxt
         warmup = self.mcmc_sample.metadata.cmdstan_config['save_warmup']
         num_draws = self.mcmc_sample.draws(inc_warmup=warmup).shape[0]
-        gq_sample = np.empty(
+        gq_sample: np.ndarray = np.empty(
             (num_draws, self.chains, len(self.column_names)),
             dtype=float,
             order='F',
diff --git a/cmdstanpy/stanfit/mle.py b/cmdstanpy/stanfit/mle.py
index a6f9a86d..683f680a 100644
--- a/cmdstanpy/stanfit/mle.py
+++ b/cmdstanpy/stanfit/mle.py
@@ -54,13 +54,9 @@ def _set_mle_attrs(self, sample_csv_0: str) -> None:
         meta = scan_optimize_csv(sample_csv_0, self._save_iterations)
         self._metadata = InferenceMetadata(meta)
         self._column_names: Tuple[str, ...] = meta['column_names']
-        assert isinstance(meta['mle'], np.ndarray)  # make the typechecker happy
-        self._mle = meta['mle']
+        self._mle: np.ndarray = meta['mle']
         if self._save_iterations:
-            assert isinstance(
-                meta['all_iters'], np.ndarray
-            )  # make the typechecker happy
-            self._all_iters = meta['all_iters']
+            self._all_iters: np.ndarray = meta['all_iters']
 
     @property
     def column_names(self) -> Tuple[str, ...]:
@@ -202,13 +198,13 @@ def stan_variable(
             num_rows = self._all_iters.shape[0]
         else:
             num_rows = 1
+
+        result: Union[np.ndarray, float]
         if len(col_idxs) > 1:  # container var
             dims = (num_rows,) + self._metadata.stan_vars_dims[var]
             # pylint: disable=redundant-keyword-arg
             if num_rows > 1:
-                result = self._all_iters[:, col_idxs].reshape(  # type: ignore
-                    dims, order='F'
-                )
+                result = self._all_iters[:, col_idxs].reshape(dims, order='F')
             else:
                 result = self._mle[col_idxs].reshape(dims[1:], order="F")
         else:  # scalar var
@@ -217,9 +213,7 @@ def stan_variable(
                 result = self._all_iters[:, col_idx]
             else:
                 result = float(self._mle[col_idx])
-        assert isinstance(
-            result, (np.ndarray, float)
-        )  # make the typechecker happy
+
         return result
 
     def stan_variables(
diff --git a/cmdstanpy/stanfit/vb.py b/cmdstanpy/stanfit/vb.py
index f094a7d3..7819c77e 100644
--- a/cmdstanpy/stanfit/vb.py
+++ b/cmdstanpy/stanfit/vb.py
@@ -126,6 +126,7 @@ def stan_variable(
             raise ValueError('Unknown variable name: {}'.format(var))
         col_idxs = list(self._metadata.stan_vars_cols[var])
         shape: Tuple[int, ...] = ()
+        result: Union[np.ndarray, float]
         if len(col_idxs) > 1:
             shape = self._metadata.stan_vars_dims[var]
             result = np.asarray(self._variational_mean)[col_idxs].reshape(
@@ -133,7 +134,6 @@ def stan_variable(
             )
         else:
             result = float(self._variational_mean[col_idxs[0]])
-        assert isinstance(result, (np.ndarray, float))
         return result
 
     def stan_variables(self) -> Dict[str, Union[np.ndarray, float]]:
diff --git a/cmdstanpy/utils.py b/cmdstanpy/utils.py
index afe5c080..ccdca660 100644
--- a/cmdstanpy/utils.py
+++ b/cmdstanpy/utils.py
@@ -639,7 +639,7 @@ def scan_optimize_csv(path: str, save_iters: bool = False) -> Dict[str, Any]:
         for line in fd:
             iters += 1
     if save_iters:
-        all_iters = np.empty(
+        all_iters: np.ndarray = np.empty(
             (iters, len(dict['column_names'])), dtype=float, order='F'
         )
     # rescan to capture estimates
@@ -658,7 +658,7 @@ def scan_optimize_csv(path: str, save_iters: bool = False) -> Dict[str, Any]:
             if save_iters:
                 all_iters[i, :] = [float(x) for x in xs]
             if i == iters - 1:
-                mle = np.array(xs, dtype=float)
+                mle: np.ndarray = np.array(xs, dtype=float)
     dict['mle'] = mle
     if save_iters:
         dict['all_iters'] = all_iters
@@ -944,7 +944,7 @@ def read_metric(path: str) -> List[int]:
         with open(path, 'r') as fd:
             metric_dict = json.load(fd)
         if 'inv_metric' in metric_dict:
-            dims_np = np.asarray(metric_dict['inv_metric'])
+            dims_np: np.ndarray = np.asarray(metric_dict['inv_metric'])
             return list(dims_np.shape)
         else:
             raise ValueError(
diff --git a/pyproject.toml b/pyproject.toml
index 8bdfc60b..a1f4b649 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -14,16 +14,17 @@ line_length = 80
 disallow_untyped_defs = true
 disallow_incomplete_defs = true
 no_implicit_optional = true
-# disallow_any_generics = true # disabled due to issues with numpy < 1.20
+# disallow_any_generics = true # disabled due to issues with numpy
 warn_return_any = true
 # warn_unused_ignores = true # can't be run on CI due to windows having different ctypes
+check_untyped_defs = true
+warn_redundant_casts = true
+strict_equality = true
+disallow_untyped_calls = true
 
 [[tool.mypy.overrides]]
 module = [
     'tqdm.auto',
     'pandas',
-    'ujson',
-    'numpy', # these two are required for py36, which numpy 1.21 doesn't support
-    'numpy.random'
     ]
 ignore_missing_imports = true
diff --git a/requirements-test.txt b/requirements-test.txt
index 2506c7c1..de7b489b 100644
--- a/requirements-test.txt
+++ b/requirements-test.txt
@@ -7,3 +7,4 @@ mypy
 testfixtures
 tqdm
 xarray
+types-ujson
diff --git a/setup.py b/setup.py
index efe16632..fb6dd683 100644
--- a/setup.py
+++ b/setup.py
@@ -80,6 +80,7 @@ def get_version() -> str:
         ]
     },
     install_requires=INSTALL_REQUIRES,
+    python_requires='>=3.7',
     extras_require=EXTRAS_REQUIRE,
     classifiers=_classifiers.strip().split('\n'),
 )