diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index 395040b..e247664 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -22,7 +22,7 @@ jobs:
       fail-fast: false  # Changed to false to see all failures
       matrix:
         os: [ ubuntu-latest, windows-latest, macos-latest, ubuntu-24.04-arm ]
-        python-version: [ "3.8","3.9","3.10", "3.11","3.12", "3.13", "3.14" ]
+        python-version: ["3.10", "3.11","3.12", "3.13", "3.14" ]
 
     steps:
       - uses: actions/checkout@v4
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index e1debd7..a3945b3 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,6 +1,6 @@
 repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v5.0.0
+    rev: v6.0.0
     hooks:
       - id: check-ast
       - id: check-case-conflict
@@ -19,7 +19,7 @@ repos:
       - id: requirements-txt-fixer
 
   - repo: https://github.com/pre-commit/mirrors-mypy
-    rev: v1.15.0
+    rev: v1.19.1
     hooks:
       - id: mypy
         files: .
@@ -41,7 +41,7 @@ repos:
         ]
 
   - repo: https://github.com/psf/black
-    rev: 25.1.0 # Replace by any tag/version: https://github.com/psf/black/tags
+    rev: 26.1.0 # Replace by any tag/version: https://github.com/psf/black/tags
     hooks:
       - id: black
         files: ^python/
@@ -49,14 +49,14 @@ repos:
         language_version: python3 # Should be a command that runs python3.6+
 
   - repo: https://github.com/pycqa/isort
-    rev: 6.0.1
+    rev: 8.0.0
     hooks:
       - id: isort
         files: ^python/
         args: [ "--profile", "black", "--settings-file", "python/pyproject.toml" ]
 
   - repo: https://github.com/pycqa/pylint
-    rev: v3.3.6
+    rev: v4.0.5
     hooks:
       - id: pylint
         files: ^python/
@@ -65,7 +65,7 @@ repos:
 
   - repo: https://github.com/charliermarsh/ruff-pre-commit
     # Ruff version.
-    rev: 'v0.11.7'
+    rev: 'v0.15.4'
     hooks:
       - id: ruff
         files: ^python/
@@ -73,7 +73,7 @@ repos:
                 "--exit-non-zero-on-fix" ] # don't use --fix as it corrupts the files
 
   - repo: https://github.com/kynan/nbstripout
-    rev: 0.8.1
+    rev: 0.9.1
     hooks:
       - id: nbstripout
         files: ^python/
\ No newline at end of file
diff --git a/setup.py b/setup.py
index 4d359ca..aab9992 100644
--- a/setup.py
+++ b/setup.py
@@ -6,7 +6,7 @@
 __author__ = 'ASU'
 
 # Bump up this version
-VERSION = '0.2.17'
+VERSION = '0.2.18'
 
 basedir = path.abspath(path.dirname(__file__))
 
@@ -27,7 +27,7 @@
     # https://packaging.python.org/en/latest/single_source_version.html
     version=VERSION,
 
-    description='TimeStam eXtensions for Python',
+    description='TimeStamp eXtensions for Python',
     long_description=long_description,
     long_description_content_type="text/markdown",
 
diff --git a/tests/test_ts.py b/tests/test_ts.py
index a5c3307..3e768a0 100644
--- a/tests/test_ts.py
+++ b/tests/test_ts.py
@@ -548,7 +548,7 @@ def test_from_ints(self):
 
         ts = iTSns.from_parts(2022, 12, 7, 1, 2, 3, 456, 789, 999, tzinfo="Europe/Berlin")
         self.assertEqual(ts, iTSns("2022-12-07T00:02:03.456789999Z"))  # we don't have enough float precision to represent nanos
-        self.assertEqual(ts.iso_tz("Europe/Bucharest"), "2022-12-07T00:02:03.456790+02:00")  # we don't have enough float precision to represent nanos
+        self.assertEqual(ts.iso_tz("Europe/Bucharest"), "2022-12-07T02:02:03.456790+02:00")  # we don't have enough float precision to represent nanos
 
         ts = iTSms.from_parts(2022, 6, 7, 1, 2, 3, 456, 789, 999, tzinfo="Europe/Bucharest")
         self.assertEqual(ts, iTSms("2022-06-06T22:02:03.456Z"))
@@ -732,6 +732,9 @@ def test_as_iso_tz_standard(self):
         res = ts.iso_tz("Europe/Bucharest")
         self.assertEqual(res, "2018-03-01T02:00:00+02:00")
 
+        res = iTSns("2018-06-01T00:00:00.123456789Z").iso_tz("Europe/Bucharest")
+        self.assertEqual(res, "2018-06-01T03:00:00.123457+03:00")
+
     def test_as_iso_tz_DST(self):
         ts = iTS("2020-06-01T10:00:00Z")
         res = ts.iso_tz(pytz.timezone("Europe/Bucharest"))
@@ -1011,6 +1014,16 @@ def test_str(self):
         ts = iTSms(ts=TestTS.INT_BASE_MS_TS)
         self.assertEqual(TestTS.STR_MSEC_TS, str(ts))
 
+    def test_as_iso_tz_standard(self):
+        ts = iTSms("2018-03-01T00:00:00Z")
+        res = ts.iso_tz(pytz.timezone("Europe/Bucharest"))
+        self.assertEqual(res, "2018-03-01T02:00:00+02:00")
+        res = ts.iso_tz("Europe/Bucharest")
+        self.assertEqual(res, "2018-03-01T02:00:00+02:00")
+
+        res = iTSns("2018-06-01T00:00:00.123456789Z").iso_tz("Europe/Bucharest")
+        self.assertEqual(res, "2018-06-01T03:00:00.123457+03:00")
+
     def test_pydantic_validator(self):
         class TestModel(BaseModel):
             ts: iTSms
@@ -1064,6 +1077,26 @@ class Test_iTSus(TestCase):
     def test_from_iso(self):
         run_test_from_iso(self, iTSus)
 
+    def test_as_dt_tz_conversion_preserves_instant_regression(self):
+        ts = iTSus("2018-03-01T00:00:00.123456Z")
+        dt_utc = ts.as_dt(timezone.utc)
+        dt_buc = ts.as_dt("Europe/Bucharest")
+
+        # Same instant, different timezone representation.
+        self.assertEqual(dt_utc.timestamp(), dt_buc.timestamp())
+        self.assertEqual(dt_utc.isoformat(), "2018-03-01T00:00:00.123456+00:00")
+        self.assertEqual(dt_buc.isoformat(), "2018-03-01T02:00:00.123456+02:00")
+
+        res = iTSns("2018-06-01T00:00:00.123456789Z").iso_tz("Europe/Bucharest")
+        self.assertEqual(res, "2018-06-01T03:00:00.123457+03:00")
+
+    def test_as_iso_tz_standard(self):
+        ts = iTSus("2018-03-01T00:00:00.123456Z")
+        res = ts.iso_tz(pytz.timezone("Europe/Bucharest"))
+        self.assertEqual(res, "2018-03-01T02:00:00.123456+02:00")
+        res = ts.iso_tz("Europe/Bucharest")
+        self.assertEqual(res, "2018-03-01T02:00:00.123456+02:00")
+
     def test_regression_iso_basic_precision(self):
         its = iTSus("2025-10-07T13:11:21.098321Z")
         self.assertEqual("2025-10-07T13:11:21.098321Z", its.isoformat())
@@ -1178,6 +1211,17 @@ class Test_iTSns(TestCase):
     def test_from_iso(self):
         run_test_from_iso(self, iTSns)
 
+    def test_as_iso_tz_standard(self):
+        ts = iTSns("2018-03-01T00:00:00.123456789Z")
+        # as_dt() is microsecond-based for iTSns via as_usec(), so TZ conversion rounds to microseconds.
+        res = ts.iso_tz(pytz.timezone("Europe/Bucharest"))
+        self.assertEqual(res, "2018-03-01T02:00:00.123457+02:00")
+        res = ts.iso_tz("Europe/Bucharest")
+        self.assertEqual(res, "2018-03-01T02:00:00.123457+02:00")
+
+        res = iTSns("2018-06-01T00:00:00.123456789Z").iso_tz("Europe/Bucharest")
+        self.assertEqual(res, "2018-06-01T03:00:00.123457+03:00")
+
     def test_regression_itsns_constructor_vs_from_iso(self):
         """Test that iTSns() and iTSns.from_iso() produce the same result"""
         date_str = "2025-11-02T13:45:14.012345678Z"
diff --git a/tsx/ts.py b/tsx/ts.py
index 86ee0c0..d0583e2 100644
--- a/tsx/ts.py
+++ b/tsx/ts.py
@@ -227,7 +227,7 @@ def from_parts_utc(cls, y: int, m: int = 1, d: int = 1, hh: int = 0, mm: int = 0
 
     @classmethod
     def from_parts(cls, y: int, m: int = 1, d: int = 1, hh: int = 0, mm: int = 0, ss: int = 0, ms: int = 0, us: int = 0, ns: int = 0,
-                   tzinfo: Union[str, dt_tzinfo] = timezone.utc) -> Self:
+                   tzinfo: dt_tzinfo | str = timezone.utc) -> Self:
         total_us = ms * 1000 + us
         if isinstance(tzinfo, str):
             tzinfo = pytz.timezone(tzinfo)
@@ -380,7 +380,7 @@ def timestamp(self) -> "TS":
         """
         raise NotImplementedError()
 
-    def as_dt(self, tz: Union[dt_tzinfo, str] = timezone.utc) -> datetime:
+    def as_dt(self, tz: dt_tzinfo | str = timezone.utc) -> datetime:
         """
         Returns an "aware" datetime object in UTC by default
         """
@@ -388,10 +388,9 @@ def as_dt(self, tz: Union[dt_tzinfo, str] = timezone.utc) -> datetime:
         try:
             if isinstance(tz, str):
                 tz = pytz.timezone(tz)
-                naive_dt = datetime.fromtimestamp(int(self))
-                dt = tz.localize(naive_dt)
-            else:
-                dt = datetime.fromtimestamp(ts, tz=tz)
+            dt = datetime.fromtimestamp(ts, tz=timezone.utc)
+            if tz != timezone.utc:
+                dt = dt.astimezone(tz)
             return dt
         except OSError:
             # can't convert due to overflow error, so we need to do it using other method
@@ -399,11 +398,13 @@ def as_dt(self, tz: Union[dt_tzinfo, str] = timezone.utc) -> datetime:
             days = ts // SECONDS_PER_DAY
             years = int(days / AVG_DAYS_PER_YEAR)  # Average considering leap years
             year = 1970 + years
-            year_date = datetime(year, 1, 1, tzinfo=tz)
-            td_to_year_beginning = year_date - datetime(1970, 1, 1, tzinfo=tz)
+            year_date = datetime(year, 1, 1, tzinfo=timezone.utc)
+            td_to_year_beginning = year_date - datetime(1970, 1, 1, tzinfo=timezone.utc)
             year_remaining_sec = ts - td_to_year_beginning.total_seconds()
             td = timedelta(seconds=year_remaining_sec)
             res = year_date + td
+            if tz != timezone.utc:
+                res = res.astimezone(tz)
             return res
 
     def as_local_dt(self) -> datetime:
@@ -466,7 +467,7 @@ def iso_date_basic(self, use_zulu: bool = False) -> str:
         """
         return self.iso_date(sep="", use_zulu=use_zulu)
 
-    def iso_tz(self, tz: Union[str, dt_tzinfo]) -> str:
+    def iso_tz(self, tz: dt_tzinfo | str) -> str:
         """
         Returns ISO date format with TZ info.
         Example: 2021-01-01
@@ -660,7 +661,7 @@ def as_iso_date_basic(self) -> str:
         s = self.as_dt().strftime("%Y%m%d")
         return s
 
-    def as_iso_tz(self, tz: Union[str, dt_tzinfo]) -> str:
+    def as_iso_tz(self, tz: dt_tzinfo | str) -> str:
         if isinstance(tz, str):
             tz = pytz.timezone(tz)
         dt = self.as_dt(tz=tz)
@@ -842,7 +843,7 @@ def __setattr__(self, name: str, value: Any) -> None:
         object.__setattr__(self, name, value)
 
     @classmethod
-    def from_year(cls, year: int, tz: Union[str, dt_tzinfo] = timezone.utc, dtype:Optional[Type[BaseTS]]=None) -> "TSInterval":
+    def from_year(cls, year: int, tz: dt_tzinfo | str = timezone.utc, dtype:Optional[Type[BaseTS]]=None) -> "TSInterval":
         """
         Create an interval covering the full calendar year in the requested timezone (defaults to UTC).
         """
@@ -1107,7 +1108,7 @@ class iBaseTS(BaseTS, int):
     @override
     @classmethod
     def from_parts(cls, y: int, m: int = 1, d: int = 1, hh: int = 0, mm: int = 0, ss: int = 0, ms: int = 0, us: int = 0, ns: int = 0,
-                   tzinfo: Union[str, dt_tzinfo] = timezone.utc) -> Self:
+                   tzinfo: dt_tzinfo | str = timezone.utc) -> Self:
         if isinstance(tzinfo, str):
             tzinfo = pytz.timezone(tzinfo)
             naive_dt = datetime(y, m, d, hh, mm, ss, 0)
@@ -1256,16 +1257,16 @@ def _get_auto_timespec(self) -> str:
         """
         return "seconds"
 
-    def as_dt(self, tz: Union[str, dt_tzinfo] = timezone.utc) -> datetime:
+    def as_dt(self, tz: dt_tzinfo | str = timezone.utc) -> datetime:
         """
         Returns an "aware" datetime object in UTC by default
         """
         if isinstance(tz, str):
             tz = pytz.timezone(tz)
-            naive_dt = datetime.fromtimestamp(int(self))
-            return tz.localize(naive_dt)
         assert isinstance(tz, dt_tzinfo)
-        utc_dt = datetime.fromtimestamp(int(self), tz=tz)
+        utc_dt = datetime.fromtimestamp(int(self), tz=timezone.utc)
+        if tz != timezone.utc:
+            utc_dt = utc_dt.astimezone(tz)
         return utc_dt
 
 
@@ -1306,12 +1307,16 @@ def __new__(cls, ts: Union[int, float, str], utc: bool = True):
     def as_msec(self) -> "iTSms":
         return self
 
-    def as_dt(self, tz: dt_tzinfo = timezone.utc) -> datetime:
+    def as_dt(self, tz: dt_tzinfo | str = timezone.utc) -> datetime:
         """
         Returns an "aware" datetime object in UTC by default
         """
         seconds, ms = divmod(self, 1000)
-        return datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=seconds, milliseconds=ms)
+        utc_dt = datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=seconds, milliseconds=ms)
+        if isinstance(tz, str):
+            tz = pytz.timezone(tz)
+        assert isinstance(tz, dt_tzinfo)
+        return utc_dt.astimezone(tz)
 
     def _get_auto_timespec(self) -> str:
         """
@@ -1376,19 +1381,16 @@ def _get_auto_timespec(self) -> str:
         """
         return "microseconds"
 
-    def as_dt(self, tz: Union[str, dt_tzinfo] = timezone.utc) -> datetime:
+    def as_dt(self, tz: dt_tzinfo | str = timezone.utc) -> datetime:
         """
         Returns an "aware" datetime object in UTC by default
         """
         seconds, us = divmod(self, 1_000_000)
+        utc_dt = datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=seconds, microseconds=us)
         if isinstance(tz, str):
             tz = pytz.timezone(tz)
-            naive_dt = EPOCH_DT + timedelta(seconds=seconds, microseconds=us)
-            dt = tz.localize(naive_dt)
-        else:
-            assert isinstance(tz, dt_tzinfo)
-            dt = datetime(1970, 1, 1, tzinfo=tz) + timedelta(seconds=seconds, microseconds=us)
-        return dt
+        assert isinstance(tz, dt_tzinfo)
+        return utc_dt.astimezone(tz)
 
     def iso_basic(self, sep="-", use_zulu: bool = True) -> str:
         """
@@ -1505,7 +1507,7 @@ def as_usec(self) -> "iTSus":
             us += 1
         return iTSus(us)
 
-    def as_dt(self, tz: Union[str, dt_tzinfo] = timezone.utc) -> datetime:
+    def as_dt(self, tz: dt_tzinfo | str = timezone.utc) -> datetime:
         """
         Returns an "aware" datetime object in UTC by default;
         Since the datetime object has a microsecond resolution, we'll convert to iTSus and return it