diff --git a/.evergreen/run-tests.sh b/.evergreen/run-tests.sh
index f49a0e9a..85f3bd33 100644
--- a/.evergreen/run-tests.sh
+++ b/.evergreen/run-tests.sh
@@ -3,13 +3,13 @@
 set -eux
 
 # Install django-mongodb-backend
-/opt/python/3.10/bin/python3 -m venv venv
+/opt/python/3.12/bin/python3 -m venv venv
 . venv/bin/activate
 python -m pip install -U pip
 pip install -e .
 
 # Install django and test dependencies
-git clone --branch mongodb-5.2.x https://github.com/mongodb-forks/django django_repo
+git clone --branch mongodb-6.0.x https://github.com/mongodb-forks/django django_repo
 pushd django_repo/tests/
 pip install -e ..
 pip install -r requirements/py3.txt
diff --git a/.github/workflows/linters.yml b/.github/workflows/linters.yml
index dcf46d45..4bf0fa77 100644
--- a/.github/workflows/linters.yml
+++ b/.github/workflows/linters.yml
@@ -17,7 +17,7 @@ jobs:
           persist-credentials: false
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.10'
+          python-version: '3.12'
           cache: 'pip'
           cache-dependency-path: 'pyproject.toml'
       - name: Install Python dependencies
@@ -37,7 +37,7 @@ jobs:
         with:
           cache: 'pip'
           cache-dependency-path: 'pyproject.toml'
-          python-version: '3.10'
+          python-version: '3.12'
       - name: Install dependencies
         run: |
           pip install -U pip
diff --git a/.github/workflows/test-python-atlas.yml b/.github/workflows/test-python-atlas.yml
index 175dfe18..1509c014 100644
--- a/.github/workflows/test-python-atlas.yml
+++ b/.github/workflows/test-python-atlas.yml
@@ -33,7 +33,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: 'mongodb-forks/django'
-          ref: 'mongodb-5.2.x'
+          ref: 'mongodb-6.0.x'
           path: 'django_repo'
           persist-credentials: false
       - name: Install system packages for Django's Python test dependencies
diff --git a/.github/workflows/test-python.yml b/.github/workflows/test-python.yml
index d3fccebd..5f912bba 100644
--- a/.github/workflows/test-python.yml
+++ b/.github/workflows/test-python.yml
@@ -33,7 +33,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: 'mongodb-forks/django'
-          ref: 'mongodb-5.2.x'
+          ref: 'mongodb-6.0.x'
           path: 'django_repo'
           persist-credentials: false
       - name: Install system packages for Django's Python test dependencies
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index bf5dba2f..ba11945f 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -21,6 +21,6 @@ python:
           - docs
 
 build:
-  os: ubuntu-22.04
+  os: ubuntu-24.04
   tools:
-    python: "3.11"
+    python: "3.12"
diff --git a/django_mongodb_backend/__init__.py b/django_mongodb_backend/__init__.py
index 00700421..f57b3e7c 100644
--- a/django_mongodb_backend/__init__.py
+++ b/django_mongodb_backend/__init__.py
@@ -1,4 +1,4 @@
-__version__ = "5.2.0b2.dev0"
+__version__ = "6.0.0b0.dev0"
 
 # Check Django compatibility before other imports which may fail if the
 # wrong version of Django is installed.
diff --git a/django_mongodb_backend/aggregates.py b/django_mongodb_backend/aggregates.py
index e67cefa2..93df6be0 100644
--- a/django_mongodb_backend/aggregates.py
+++ b/django_mongodb_backend/aggregates.py
@@ -1,5 +1,12 @@
-from django.db.models.aggregates import Aggregate, Count, StdDev, Variance
-from django.db.models.expressions import Case, Value, When
+from django.db.models.aggregates import (
+    Aggregate,
+    AggregateFilter,
+    Count,
+    StdDev,
+    StringAgg,
+    Variance,
+)
+from django.db.models.expressions import Case, Col, Value, When
 from django.db.models.lookups import IsNull
 
 from .query_utils import process_lhs
@@ -16,7 +23,11 @@ def aggregate(
     resolve_inner_expression=False,
     **extra_context,  # noqa: ARG001
 ):
-    if self.filter:
+    # TODO: isinstance(self.filter, Col) works around failure of
+    # aggregation.tests.AggregateTestCase.test_distinct_on_aggregate. Is this
+    # correct?
+    if self.filter is not None and not isinstance(self.filter, Col):
+        # Generate a CASE statement for this aggregate.
         node = self.copy()
         node.filter = None
         source_expressions = node.get_source_expressions()
@@ -31,6 +42,10 @@ def aggregate(
     return {f"${operator}": lhs_mql}
 
 
+def aggregate_filter(self, compiler, connection, **extra_context):
+    return self.condition.as_mql(compiler, connection, **extra_context)
+
+
 def count(self, compiler, connection, resolve_inner_expression=False, **extra_context):  # noqa: ARG001
     """
     When resolve_inner_expression=True, return the MQL that resolves as a
@@ -72,8 +87,16 @@ def stddev_variance(self, compiler, connection, **extra_context):
     return aggregate(self, compiler, connection, operator=operator, **extra_context)
 
 
+def string_agg(self, compiler, connection, **extra_context):  # # noqa: ARG001
+    from django.db import NotSupportedError
+
+    raise NotSupportedError("StringAgg is not supported.")
+
+
 def register_aggregates():
     Aggregate.as_mql = aggregate
+    AggregateFilter.as_mql = aggregate_filter
     Count.as_mql = count
     StdDev.as_mql = stddev_variance
+    StringAgg.as_mql = string_agg
     Variance.as_mql = stddev_variance
diff --git a/django_mongodb_backend/cache.py b/django_mongodb_backend/cache.py
index 00b903af..ae4809a2 100644
--- a/django_mongodb_backend/cache.py
+++ b/django_mongodb_backend/cache.py
@@ -1,5 +1,5 @@
 import pickle
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
 from django.core.cache.backends.db import Options
@@ -72,7 +72,7 @@ def get_backend_timeout(self, timeout=DEFAULT_TIMEOUT):
         if timeout is None:
             return datetime.max
         timestamp = super().get_backend_timeout(timeout)
-        return datetime.fromtimestamp(timestamp, tz=timezone.utc)
+        return datetime.fromtimestamp(timestamp, tz=UTC)
 
     def get(self, key, default=None, version=None):
         return self.get_many([key], version).get(key, default)
diff --git a/django_mongodb_backend/features.py b/django_mongodb_backend/features.py
index fa73461d..63f5ce0c 100644
--- a/django_mongodb_backend/features.py
+++ b/django_mongodb_backend/features.py
@@ -86,6 +86,21 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         # Value.as_mql() doesn't call output_field.get_db_prep_save():
         # https://github.com/mongodb/django-mongodb-backend/issues/282
         "model_fields.test_jsonfield.TestSaveLoad.test_bulk_update_custom_get_prep_value",
+        # This backend overrides DatabaseCreation.create_test_db() so the
+        # deprecation warnings stacklevel points to the wrong file.
+        "backends.base.test_creation.TestDbCreationTests.test_serialize_deprecation",
+        # StringAgg is not supported.
+        "aggregation.tests.AggregateTestCase.test_distinct_on_stringagg",
+        "aggregation.tests.AggregateTestCase.test_string_agg_escapes_delimiter",
+        "aggregation.tests.AggregateTestCase.test_string_agg_filter",
+        "aggregation.tests.AggregateTestCase.test_string_agg_filter_in_subquery",
+        "aggregation.tests.AggregateTestCase.test_stringagg_default_value",
+        # bulk_create() population of _order not implemented.
+        # https://github.com/django/django/commit/953095d1e603fe0f8f01175b1409ca23818dcff9
+        "contenttypes_tests.test_order_with_respect_to.OrderWithRespectToGFKTests.test_bulk_create_allows_duplicate_order_values",
+        "contenttypes_tests.test_order_with_respect_to.OrderWithRespectToGFKTests.test_bulk_create_mixed_scenario",
+        "contenttypes_tests.test_order_with_respect_to.OrderWithRespectToGFKTests.test_bulk_create_respects_mixed_manual_order",
+        "contenttypes_tests.test_order_with_respect_to.OrderWithRespectToGFKTests.test_bulk_create_with_existing_children",
     }
     # $bitAnd, #bitOr, and $bitXor are new in MongoDB 6.3.
     _django_test_expected_failures_bitwise = {
diff --git a/django_mongodb_backend/fields/json.py b/django_mongodb_backend/fields/json.py
index b7cf49dc..24c640b4 100644
--- a/django_mongodb_backend/fields/json.py
+++ b/django_mongodb_backend/fields/json.py
@@ -24,7 +24,12 @@ def build_json_mql_path(lhs, key_transforms):
         get_field = {"$getField": {"input": result, "field": key}}
         # Handle array indexing if the key is a digit. If key is something
         # like '001', it's not an array index despite isdigit() returning True.
-        if key.isdigit() and str(int(key)) == key:
+        try:
+            int(key)
+            is_digit = str(int(key)) == key
+        except ValueError:
+            is_digit = False
+        if is_digit:
             result = {
                 "$cond": {
                     "if": {"$isArray": result},
diff --git a/pyproject.toml b/pyproject.toml
index 7b412e1d..8f100a98 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,7 +8,7 @@ dynamic = ["version", "dependencies"]
 description = "Django MongoDB Backend"
 readme = "README.md"
 license = {file="LICENSE"}
-requires-python = ">=3.10"
+requires-python = ">=3.12"
 authors = [
     { name = "The MongoDB Python Team" },
 ]
@@ -27,8 +27,6 @@ classifiers = [
     "Operating System :: OS Independent",
     "Programming Language :: Python :: 3",
     "Programming Language :: Python :: 3 :: Only",
-    "Programming Language :: Python :: 3.10",
-    "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
 ]