diff --git a/lib/galaxy_test/shard.py b/lib/galaxy_test/shard.py
new file mode 100644
index 00000000000..140cc3c1605
--- /dev/null
+++ b/lib/galaxy_test/shard.py
@@ -0,0 +1,121 @@
+"""Distribute tests across CI shards without splitting up test classes.
+
+An integration test class boots a Galaxy instance in ``setUpClass``, so a class split
+across shards makes every one of them pay that startup. Whole classes are kept together
+and packed into shards longest-first, weighted by recorded durations, which balances
+shards by cost rather than by name.
+"""
+
+import json
+import os
+from collections import defaultdict
+from typing import (
+    Any,
+    NamedTuple,
+)
+
+import pytest
+
+DURATIONS_ENV_VAR = "GALAXY_TEST_SHARD_DURATIONS"
+# Per-group seconds measured from a CI run, as {"module::Class": seconds}. Only affects
+# balance, never correctness: unknown groups get DEFAULT_GROUP_SECONDS. Regenerate from a
+# full unsharded run with --structured_data_report_file, summing each test's setup, call
+# and teardown into its group_key(). GALAXY_TEST_SHARD_DURATIONS overrides the path.
+DEFAULT_DURATIONS_FILE = os.path.join(os.path.dirname(__file__), "shard_durations.json")
+# What to assume a group costs when we have no measurement for it. Integration classes
+# are startup-dominated, so an unknown group is much closer to one startup than to zero.
+DEFAULT_GROUP_SECONDS = 40.0
+
+
+class ShardGroup(NamedTuple):
+    """Tests that share a Galaxy instance, and therefore must share a shard."""
+
+    key: str
+    items: list[Any]
+    seconds: float
+
+
+def group_key(item) -> str:
+    """Identify the instance an item belongs to.
+
+    Class for class-based tests, module for those taking a module-scoped instance
+    fixture, and the file for items with no module at all.
+    """
+    module = getattr(item, "module", None)
+    if module is None:
+        return item.nodeid.split("::")[0]
+    cls = getattr(item, "cls", None)
+    if cls is not None:
+        return f"{module.__name__}::{cls.__name__}"
+    return module.__name__
+
+
+def load_durations(path: str | None = None) -> dict[str, float]:
+    """Load recorded per-group durations, falling back to an empty mapping."""
+    path = path or os.environ.get(DURATIONS_ENV_VAR) or DEFAULT_DURATIONS_FILE
+    try:
+        with open(path) as fh:
+            return {key: float(seconds) for key, seconds in json.load(fh).items()}
+    except (OSError, ValueError):
+        return {}
+
+
+def build_groups(items: list[Any], durations: dict[str, float]) -> list[ShardGroup]:
+    grouped: dict[str, list[Any]] = defaultdict(list)
+    for item in items:
+        grouped[group_key(item)].append(item)
+    return [
+        ShardGroup(key, group_items, durations.get(key, DEFAULT_GROUP_SECONDS)) for key, group_items in grouped.items()
+    ]
+
+
+def assign_groups_to_shards(groups: list[ShardGroup], num_shards: int) -> list[list[ShardGroup]]:
+    """Pack groups into shards longest-first, always onto the shard with the least work.
+
+    Greedy bin-packing. Ties break on group key: every shard runs this independently and
+    the assignments must agree, or tests get dropped or duplicated.
+    """
+    shards: list[list[ShardGroup]] = [[] for _ in range(num_shards)]
+    loads = [0.0] * num_shards
+    for group in sorted(groups, key=lambda g: (-g.seconds, g.key)):
+        target = min(range(num_shards), key=lambda index: (loads[index], index))
+        shards[target].append(group)
+        loads[target] += group.seconds
+    return shards
+
+
+def select_shard(items: list[Any], shard_id: int, num_shards: int, durations: dict[str, float]) -> list[Any]:
+    groups = build_groups(items, durations)
+    assigned = assign_groups_to_shards(groups, num_shards)[shard_id]
+    selected = []
+    for group in sorted(assigned, key=lambda g: g.key):
+        selected.extend(group.items)
+    return selected
+
+
+def pytest_configure(config) -> None:
+    """Take over sharding from pytest-shard, reusing its command line options."""
+    shard_plugin = config.pluginmanager.get_plugin("pytest-shard")
+    if shard_plugin is not None:
+        config.pluginmanager.unregister(shard_plugin)
+
+
+def pytest_report_collectionfinish(config, items) -> str | None:
+    """Report which groups this shard runs."""
+    num_shards = config.getoption("num_shards", default=1)
+    if num_shards <= 1:
+        return None
+    groups = sorted({group_key(item) for item in items})
+    shard_id = config.getoption("shard_id", default=0)
+    return f"Running {len(items)} items from {len(groups)} groups in shard {shard_id}: {', '.join(groups)}"
+
+
+@pytest.hookimpl(trylast=True)
+def pytest_collection_modifyitems(config, items: list[Any]) -> None:
+    num_shards = config.getoption("num_shards", default=1)
+    shard_id = config.getoption("shard_id", default=0)
+    if num_shards <= 1:
+        return
+    if shard_id >= num_shards:
+        raise ValueError(f"shard_id = {shard_id} must be less than num_shards = {num_shards}")
+    items[:] = select_shard(items, shard_id, num_shards, load_durations())
diff --git a/lib/galaxy_test/shard_durations.json b/lib/galaxy_test/shard_durations.json
new file mode 100644
index 00000000000..9472c4d9d60
--- /dev/null
+++ b/lib/galaxy_test/shard_durations.json
@@ -0,0 +1,271 @@
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+  "integration.objectstore.test_per_user::TestPerUserObjectStoreWithExtendedMetadataIntegration": 45.1,
+  "integration.objectstore.test_per_user::TestPerUserObjectStoreWithSecretsIntegration": 68.5,
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+  "integration.test_upload_configuration_options::TestServerDirectoryOffByDefault": 26.4,
+  "integration.test_upload_configuration_options::TestServerDirectoryValidUsage": 40.2,
+  "integration.test_upload_configuration_options::TestSimpleFtpUploadConfiguration": 29.3,
+  "integration.test_upload_configuration_options::TestTemplatedFtpDirectoryUploadConfiguration": 30.2,
+  "integration.test_upload_configuration_options::TestUploadOptionsFtpUploadConfiguration": 52.2,
+  "integration.test_upload_configuration_options::TestUploadWithDirectoryMetadata": 30.6,
+  "integration.test_upload_configuration_options::TestUploadWithExtendedMetadata": 29.3,
+  "integration.test_upload_configuration_options::TestUserServerDirectoryOffByDefault": 26.2,
+  "integration.test_upload_configuration_options::TestUserServerDirectoryValidUsage": 42.5,
+  "integration.test_user_defined_tool_job_conf::TestUserDefinedToolRecommendedJobSetup": 49.4,
+  "integration.test_user_defined_tool_job_conf::TestUserDefinedToolRecommendedJobSetupTPV": 69.9,
+  "integration.test_user_preferences::TestUserPreferences": 27.6,
+  "integration.test_users::TestAdminResendActivationEmail": 29.8,
+  "integration.test_users::TestExposeOnlyUserEmailIntegration": 28.9,
+  "integration.test_users::TestExposeOnlyUserNameIntegration": 27.8,
+  "integration.test_users::TestExposeUsersIntegration": 35.3,
+  "integration.test_users::TestUnexposedUsersIntegration": 28.6,
+  "integration.test_vault_extra_prefs::TestExtraUserPreferences": 33.9,
+  "integration.test_vault_file_source::TestVaultFileSourceIntegration": 29.1,
+  "integration.test_web_framework_config::TestAllowOriginIntegration": 35.9,
+  "integration.test_web_framework_config::TestCorsDefaultIntegration": 28.3,
+  "integration.test_work_queue_put_failure::TestWorkQueuePutFailure": 29.0,
+  "integration.test_workflow_completion_hooks::TestWorkflowCompletionExportHook": 34.5,
+  "integration.test_workflow_handler_configuration::TestDefaultWorkflowHandlerIfJobHandlerOff": 35.7,
+  "integration.test_workflow_handler_configuration::TestDefaultWorkflowHandlerIfJobHandlerOn": 26.7,
+  "integration.test_workflow_handler_configuration::TestDefaultWorkflowHandlerOn": 28.0,
+  "integration.test_workflow_handler_configuration::TestExplicitWorkflowHandlersOff": 27.3,
+  "integration.test_workflow_handler_configuration::TestExplicitWorkflowHandlersOffPool": 28.3,
+  "integration.test_workflow_handler_configuration::TestExplicitWorkflowHandlersOn": 24.7,
+  "integration.test_workflow_handler_configuration::TestHistoryParallelConfiguration": 26.4,
+  "integration.test_workflow_handler_configuration::TestHistoryRestrictionConfiguration": 27.4,
+  "integration.test_workflow_handler_configuration::TestJobHandlerAsWorkflowHandlerWithDbSkipLocked": 44.7,
+  "integration.test_workflow_handler_configuration::TestJobHandlerAsWorkflowHandlerWithDbSkipLockedAttachToPool": 30.0,
+  "integration.test_workflow_handler_configuration::TestWorkflowSchedulerHandlerAssignment": 39.0,
+  "integration.test_workflow_handler_configuration::TestWorkflowSchedulerHandlerAssignmentDbSkipLocked": 28.6,
+  "integration.test_workflow_handler_configuration::TestWorkflowSchedulerHandlerAssignmentDbTransactionIsolation": 28.4,
+  "integration.test_workflow_invocation::TestWorkflowInvocation": 119.6,
+  "integration.test_workflow_refactoring::TestWorkflowRefactoringIntegration": 51.2,
+  "integration.test_workflow_scheduling_options::TestMaximumWorkflowInvocationDuration": 70.5,
+  "integration.test_workflow_scheduling_options::TestMaximumWorkflowJobsPerSchedulingIteration": 55.1,
+  "integration.test_workflow_sync::TestWorkflowSync": 34.1,
+  "integration.test_workflow_tasks::TestWorkflowTasksIntegration": 398.0
+}
diff --git a/test/integration/conftest.py b/test/integration/conftest.py
index a2d8b6b5a49..bb9d878b9b6 100644
--- a/test/integration/conftest.py
+++ b/test/integration/conftest.py
@@ -7,10 +7,20 @@ from beaker.cache import CacheManager
 from beaker.util import parse_cache_config_options
 
 from galaxy.tool_util.deps.mulled.util import NAMESPACE_HAS_REPO_NAME_KEY
-from galaxy_test.conftest import (  # noqa: F401
-    pytest_configure,
-    pytest_plugins,
+from galaxy_test import shard
+from galaxy_test.conftest import pytest_plugins  # noqa: F401
+from galaxy_test.conftest import (
+    pytest_configure as _base_pytest_configure,
 )
+from galaxy_test.shard import (  # noqa: F401
+    pytest_collection_modifyitems,
+    pytest_report_collectionfinish,
+)
+
+
+def pytest_configure(config):
+    _base_pytest_configure(config)
+    shard.pytest_configure(config)
 
 
 @pytest.fixture(scope="session", autouse=True)
diff --git a/test/unit/test_shard.py b/test/unit/test_shard.py
new file mode 100644
index 00000000000..b68946fe663
--- /dev/null
+++ b/test/unit/test_shard.py
@@ -0,0 +1,101 @@
+from collections import Counter
+
+from galaxy_test.shard import (
+    assign_groups_to_shards,
+    build_groups,
+    select_shard,
+    ShardGroup,
+)
+
+
+class FakeModule:
+    def __init__(self, name):
+        self.__name__ = name
+
+
+class FakeItem:
+    def __init__(self, module_name, class_name, node_id):
+        self.module = FakeModule(module_name)
+        self.cls = type(class_name, (), {}) if class_name else None
+        self.nodeid = node_id
+
+    def __repr__(self):
+        return self.nodeid
+
+
+def make_items(*specs):
+    return [FakeItem(module, cls, f"{module}::{cls}::{name}") for module, cls, name in specs]
+
+
+def test_class_items_stay_in_one_group():
+    items = make_items(
+        ("test_a", "TestOne", "test_x"),
+        ("test_a", "TestOne", "test_y"),
+        ("test_a", "TestTwo", "test_z"),
+    )
+    groups = {group.key: group for group in build_groups(items, {})}
+    assert set(groups) == {"test_a::TestOne", "test_a::TestTwo"}
+    assert len(groups["test_a::TestOne"].items) == 2
+
+
+def test_module_level_items_group_by_module():
+    items = make_items(("test_a", None, "test_x"), ("test_a", None, "test_y"))
+    groups = build_groups(items, {})
+    assert len(groups) == 1
+    assert groups[0].key == "test_a"
+
+
+def test_unknown_groups_get_a_default_weight():
+    groups = build_groups(make_items(("test_a", "TestOne", "test_x")), {})
+    assert groups[0].seconds > 0
+
+
+def test_recorded_durations_are_used():
+    groups = build_groups(make_items(("test_a", "TestOne", "test_x")), {"test_a::TestOne": 123.0})
+    assert groups[0].seconds == 123.0
+
+
+def test_longest_group_lands_on_its_own_shard():
+    groups = [
+        ShardGroup("slow", [], 100.0),
+        ShardGroup("a", [], 10.0),
+        ShardGroup("b", [], 10.0),
+        ShardGroup("c", [], 10.0),
+    ]
+    shards = assign_groups_to_shards(groups, 2)
+    loads = sorted(sum(group.seconds for group in shard) for shard in shards)
+    assert loads == [30.0, 100.0]
+
+
+def test_assignment_is_deterministic_for_equal_weights():
+    groups = [ShardGroup(key, [], 10.0) for key in ("d", "a", "c", "b")]
+    first = assign_groups_to_shards(groups, 3)
+    second = assign_groups_to_shards(list(reversed(groups)), 3)
+    assert [[g.key for g in shard] for shard in first] == [[g.key for g in shard] for shard in second]
+
+
+def test_shards_partition_the_suite_without_splitting_classes():
+    items = make_items(
+        *[
+            (f"test_mod{module}", f"TestClass{cls}", f"test_{index}")
+            for module in range(5)
+            for cls in range(3)
+            for index in range(4)
+        ]
+    )
+    num_shards = 4
+    selected = [select_shard(items, shard_id, num_shards, {}) for shard_id in range(num_shards)]
+
+    node_ids = [item.nodeid for shard in selected for item in shard]
+    assert Counter(node_ids) == Counter(item.nodeid for item in items), "shards must partition the suite exactly"
+
+    shards_per_group: Counter[str] = Counter()
+    for shard in selected:
+        for key in {f"{item.module.__name__}::{item.cls.__name__}" for item in shard}:
+            shards_per_group[key] += 1
+    assert all(count == 1 for count in shards_per_group.values()), "a test class must not span shards"
+
+
+def test_single_shard_selects_everything():
+    items = make_items(("test_a", "TestOne", "test_x"), ("test_b", "TestTwo", "test_y"))
+    assert select_shard(items, 0, 1, {}) == items