diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f9ae68a..6df00fa 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -26,7 +26,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.10", "3.11", "3.12"]
         os: [macos, ubuntu, windows]
     steps:
       - uses: actions/checkout@v4
diff --git a/ci/environment.yml b/ci/environment.yml
index d4b3e06..0f8a0e5 100644
--- a/ci/environment.yml
+++ b/ci/environment.yml
@@ -3,7 +3,7 @@ channels:
   - conda-forge
   - nodefaults
 dependencies:
-  - python>=3.9
+  - python>=3.10
   - pandas
   - dask
   - xarray
diff --git a/intake_esgf/base.py b/intake_esgf/base.py
index 0900f77..e826d9c 100644
--- a/intake_esgf/base.py
+++ b/intake_esgf/base.py
@@ -5,7 +5,7 @@
 import time
 from functools import partial
 from pathlib import Path
-from typing import Any, Union
+from typing import Any
 
 import pandas as pd
 import requests
@@ -59,7 +59,7 @@ def combine_results(dfs: list[pd.DataFrame]) -> pd.DataFrame:
     return df
 
 
-def get_file_hash(filepath: Union[str, Path], algorithm: str) -> str:
+def get_file_hash(filepath: str | Path, algorithm: str) -> str:
     """Get the file has using the given algorithm."""
     algorithm = algorithm.lower()
     assert algorithm in hashlib.algorithms_available
@@ -75,7 +75,7 @@ def get_file_hash(filepath: Union[str, Path], algorithm: str) -> str:
 
 def download_and_verify(
     url: str,
-    local_file: Union[str, Path],
+    local_file: str | Path,
     hash: str,
     hash_algorithm: str,
     content_length: int,
@@ -126,7 +126,7 @@ def parallel_download(
     info: dict[str, Any],
     local_cache: list[Path],
     download_db: Path,
-    esg_dataroot: Union[None, list[Path]] = None,
+    esg_dataroot: None | list[Path] = None,
 ):
     """."""
     logger = intake_esgf.conf.get_logger()
@@ -168,7 +168,7 @@ def parallel_download(
 
 
 def get_search_criteria(
-    ds: xr.Dataset, project_id: Union[str, None] = None
+    ds: xr.Dataset, project_id: str | None = None
 ) -> dict[str, str]:
     """Return a dictionary of facet information from the dataset attributes."""
     if "project" in ds.attrs:
@@ -282,7 +282,7 @@ def add_cell_measures(ds: xr.Dataset, catalog) -> xr.Dataset:
     return ds
 
 
-def get_cell_measure(var: str, ds: xr.Dataset) -> Union[xr.DataArray, None]:
+def get_cell_measure(var: str, ds: xr.Dataset) -> xr.DataArray | None:
     """Return the dataarray of the measures required by the given var.
 
     This routine will examine the `cell_measures` attribute of the specified `var` as
diff --git a/intake_esgf/catalog.py b/intake_esgf/catalog.py
index 3310277..e7fd9e3 100644
--- a/intake_esgf/catalog.py
+++ b/intake_esgf/catalog.py
@@ -3,10 +3,11 @@
 import re
 import time
 import warnings
+from collections.abc import Callable
 from functools import partial
 from multiprocessing.pool import ThreadPool
 from pathlib import Path
-from typing import Callable, Literal, Union
+from typing import Literal, Union
 
 import pandas as pd
 import requests
@@ -202,7 +203,7 @@ def _extract_int_pattern(sample: str) -> str:
             .iloc[:, 0]
         )
 
-    def search(self, quiet: bool = False, **search: Union[str, list[str]]):
+    def search(self, quiet: bool = False, **search: str | list[str]):
         """Populate the catalog by specifying search facets and values.
 
         Parameters
@@ -287,9 +288,7 @@ def _search(index):
         self.last_search = search
         return self
 
-    def from_tracking_ids(
-        self, tracking_ids: Union[str, list[str]], quiet: bool = False
-    ):
+    def from_tracking_ids(self, tracking_ids: str | list[str], quiet: bool = False):
         """Populate the catalog by speciying tracking ids.
 
         While tracking_ids should uniquely define individual files, we observe that some
@@ -497,8 +496,8 @@ def _move_data(
         self,
         infos,
         num_threads,
-        globus_endpoint: Union[str, None] = None,
-        globus_path: Union[Path, None] = None,
+        globus_endpoint: str | None = None,
+        globus_path: Path | None = None,
     ):
         """Move data either by https or globus transfers."""
         logger = intake_esgf.conf.get_logger()
@@ -594,7 +593,7 @@ def _find_local_file(info):
     def to_dataset_dict(
         self,
         minimal_keys: bool = True,
-        ignore_facets: Union[None, str, list[str]] = None,
+        ignore_facets: None | str | list[str] = None,
         separator: str = ".",
         num_threads: int = 6,
         quiet: bool = False,
diff --git a/intake_esgf/config.py b/intake_esgf/config.py
index f4f8be9..d4a862e 100644
--- a/intake_esgf/config.py
+++ b/intake_esgf/config.py
@@ -4,7 +4,6 @@
 import copy
 import logging
 from pathlib import Path
-from typing import Union
 
 import yaml
 
@@ -39,7 +38,7 @@
 class Config(dict):
     """A global configuration object used in the package."""
 
-    def __init__(self, filename: Union[Path, None] = None, **kwargs):
+    def __init__(self, filename: Path | None = None, **kwargs):
         self.filename = (
             Path(filename)
             if filename is not None
@@ -58,7 +57,7 @@ def reset(self):
         self.clear()
         self.update(copy.deepcopy(defaults))
 
-    def save(self, filename: Union[Path, None] = None):
+    def save(self, filename: Path | None = None):
         """Save current configuration to file as YAML."""
         filename = filename or self.filename
         filename.parent.mkdir(parents=True, exist_ok=True)
@@ -76,9 +75,9 @@ def set(
         *,
         indices: dict[str, bool] = {},
         all_indices: bool = False,
-        esg_dataroot: Union[list[str], None] = None,
-        local_cache: Union[list[str], None] = None,
-        additional_df_cols: Union[list[str], None] = None
+        esg_dataroot: list[str] | None = None,
+        local_cache: list[str] | None = None,
+        additional_df_cols: list[str] | None = None
     ):
         """Change intake-esgf configuration options.
 
@@ -156,7 +155,7 @@ def reload_all(self):
         self.reset()
         self.load()
 
-    def load(self, filename: Union[Path, None] = None):
+    def load(self, filename: Path | None = None):
         """Update global config from YAML file or default file if None."""
         filename = filename or self.filename
         if filename.is_file():
diff --git a/intake_esgf/core/globus.py b/intake_esgf/core/globus.py
index b5eb8dd..09fffec 100644
--- a/intake_esgf/core/globus.py
+++ b/intake_esgf/core/globus.py
@@ -3,7 +3,7 @@
 import time
 from datetime import datetime
 from pathlib import Path
-from typing import Any, Union
+from typing import Any
 
 import pandas as pd
 from globus_sdk import (
@@ -39,7 +39,7 @@ def __init__(self, index_id="anl-dev"):
     def __repr__(self):
         return self.repr
 
-    def search(self, **search: Union[str, list[str]]) -> pd.DataFrame:
+    def search(self, **search: str | list[str]) -> pd.DataFrame:
         """Search the index and return as a pandas dataframe.
 
         This function uses the Globus `post_search()` function where our query consists
diff --git a/intake_esgf/core/solr.py b/intake_esgf/core/solr.py
index 68d5d67..479dcb0 100644
--- a/intake_esgf/core/solr.py
+++ b/intake_esgf/core/solr.py
@@ -1,7 +1,7 @@
 """A ESGF1 Solr index class."""
 
 import time
-from typing import Any, Union
+from typing import Any
 
 import pandas as pd
 import requests
@@ -43,7 +43,7 @@ def __init__(self, index_node: str = "esgf-node.llnl.gov", distrib: bool = False
     def __repr__(self):
         return self.repr
 
-    def search(self, **search: Union[str, list[str]]) -> pd.DataFrame:
+    def search(self, **search: str | list[str]) -> pd.DataFrame:
         search["distrib"] = search["distrib"] if "distrib" in search else self.distrib
         facets = get_project_facets(search) + intake_esgf.conf.get(
             "additional_df_cols", []
diff --git a/intake_esgf/projects.py b/intake_esgf/projects.py
index 4ecd3fa..822eee9 100644
--- a/intake_esgf/projects.py
+++ b/intake_esgf/projects.py
@@ -1,7 +1,6 @@
 """Supported projects and their facet definitions."""
 
 from abc import ABC, abstractmethod
-from typing import Union
 
 from intake_esgf.exceptions import ProjectNotSupported
 
@@ -254,7 +253,7 @@ def grid_facet(self) -> str:
 projects = {"cmip6": CMIP6(), "cmip5": CMIP5(), "cmip3": CMIP3()}
 
 
-def get_project_facets(content: dict[str, Union[str, list[str]]]) -> list[str]:
+def get_project_facets(content: dict[str, str | list[str]]) -> list[str]:
     """
     Return the facets for the project found defined in the given content.
 
@@ -280,7 +279,7 @@ def get_project_facets(content: dict[str, Union[str, list[str]]]) -> list[str]:
     return project.id_facets()
 
 
-def get_likely_project(facets: Union[list, dict]) -> str:
+def get_likely_project(facets: list | dict) -> str:
     """
     Return the project which is likely to correspond to the given facets.
 
diff --git a/pyproject.toml b/pyproject.toml
index ae40701..06a9884 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,7 +19,7 @@ addopts = "--cov=intake_esgf --cov-report=xml --verbose"
 omit = ["*/intake_esgf/tests/*"]
 
 [tool.ruff]
-target-version = "py39"
+target-version = "py310"
 ignore = [
     "E501", # line too long - let black worry about that
 ]
diff --git a/setup.cfg b/setup.cfg
index 79c126a..b62f59c 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -11,13 +11,12 @@ classifiers =
     License :: OSI Approved :: BSD License
     Operating System :: OS Independent
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
     Programming Language :: Python :: 3.12
     Intended Audience :: Science/Research
     Topic :: Scientific/Engineering
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 
 [options]
 install_requires =