diff --git a/agentlightning/client.py b/agentlightning/client.py
index 0848ce380..b232170be 100644
--- a/agentlightning/client.py
+++ b/agentlightning/client.py
@@ -22,6 +22,8 @@
 
 logger = logging.getLogger(__name__)
 
+DEFAULT_CACHE_CAPACITY = 100
+
 
 class AgentLightningClient:
     """Client wrapper for the legacy version-aware Agent Lightning server.
@@ -64,7 +66,10 @@ def __init__(self, endpoint: str, poll_interval: float = 5.0, timeout: float = 1
         self.task_count = 0
         self.poll_interval = poll_interval
         self.timeout = timeout
-        self._resource_cache: Dict[str, ResourcesUpdate] = {}  # TODO: mechanism to evict cache
+
+        from agentlightning.utils.cache import LRUCache
+
+        self._resource_cache: Dict[str, ResourcesUpdate] = LRUCache(capacity=DEFAULT_CACHE_CAPACITY)
         self._default_headers = {"X-AgentLightning-Client": "true"}
 
     async def _request_json_async(self, url: str) -> Optional[Dict[str, Any]]:
diff --git a/agentlightning/server.py b/agentlightning/server.py
index b1343fcb1..ae5320cd8 100644
--- a/agentlightning/server.py
+++ b/agentlightning/server.py
@@ -32,6 +32,8 @@
 
 logger = logging.getLogger(__name__)
 
+DEFAULT_CACHE_CAPACITY = 100
+
 
 class ServerDataStore:
     """Async-safe container for in-memory server state.
@@ -50,8 +52,10 @@ def __init__(self):
         self._processing_tasks: Dict[str, Task] = {}  # Currently processing tasks
         self._completed_rollouts: Dict[str, RolloutLegacy] = {}
 
+        from agentlightning.utils.cache import LRUCache
+
         # Store for versioned resources
-        self._resource_versions: Dict[str, NamedResources] = {}
+        self._resource_versions: Dict[str, NamedResources] = LRUCache(capacity=DEFAULT_CACHE_CAPACITY)
         self._latest_resources_id: Optional[str] = None
 
         # Locks for thread-safe access
diff --git a/agentlightning/utils/cache.py b/agentlightning/utils/cache.py
new file mode 100644
index 000000000..92151cdf5
--- /dev/null
+++ b/agentlightning/utils/cache.py
@@ -0,0 +1,41 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+from collections import OrderedDict
+from typing import Generic, Optional, TypeVar
+
+K = TypeVar("K")
+V = TypeVar("V")
+
+
+class LRUCache(OrderedDict[K, V]):
+    """A simple LRU (Least Recently Used) cache implementation using OrderedDict.
+
+    This cache has a fixed capacity. When the cache is full, adding a new item
+    discards the least recently used item.
+
+    Accessing an item (via `__getitem__` or `get`) moves it to the end, marking
+    it as recently used.
+    """
+
+    def __init__(self, capacity: int, *args, **kwargs):
+        self.capacity = capacity
+        super().__init__(*args, **kwargs)
+
+    def __getitem__(self, key: K) -> V:
+        value = super().__getitem__(key)
+        self.move_to_end(key)
+        return value
+
+    def __setitem__(self, key: K, value: V):
+        if key in self:
+            self.move_to_end(key)
+        super().__setitem__(key, value)
+        if len(self) > self.capacity:
+            self.popitem(last=False)
+
+    def get(self, key: K, default: Optional[V] = None) -> Optional[V]:
+        if key in self:
+            value = super().__getitem__(key)
+            self.move_to_end(key)
+            return value
+        return default
diff --git a/tests/test_cache_fix.py b/tests/test_cache_fix.py
new file mode 100644
index 000000000..5da731c06
--- /dev/null
+++ b/tests/test_cache_fix.py
@@ -0,0 +1,48 @@
+
+import pytest
+from agentlightning.utils.cache import LRUCache
+
+def test_lru_cache_capacity():
+    cache = LRUCache(capacity=2)
+    cache["a"] = 1
+    cache["b"] = 2
+    assert len(cache) == 2
+    
+    cache["c"] = 3
+    assert len(cache) == 2
+    assert "a" not in cache
+    assert "b" in cache
+    assert "c" in cache
+
+def test_lru_cache_access_order():
+    cache = LRUCache(capacity=2)
+    cache["a"] = 1
+    cache["b"] = 2
+    
+    # Access 'a' to make it most recently used
+    _ = cache["a"]
+    
+    # Add 'c', should evict 'b' (least recently used)
+    cache["c"] = 3
+    
+    assert "b" not in cache
+    assert "a" in cache
+    assert "c" in cache
+
+def test_integration_client_import():
+    try:
+        from agentlightning.client import AgentLightningClient
+        client = AgentLightningClient(endpoint="http://localhost:8000")
+        assert isinstance(client._resource_cache, LRUCache)
+        assert client._resource_cache.capacity == 100
+    except ImportError:
+        pytest.fail("Could not import AgentLightningClient or verify LRUCache integration")
+
+def test_integration_server_import():
+    try:
+        from agentlightning.server import ServerDataStore
+        store = ServerDataStore()
+        assert isinstance(store._resource_versions, LRUCache)
+        assert store._resource_versions.capacity == 100
+    except ImportError:
+        pytest.fail("Could not import ServerDataStore or verify LRUCache integration")