diff --git a/pydantic_ai_slim/pydantic_ai/_agent_graph.py b/pydantic_ai_slim/pydantic_ai/_agent_graph.py
index 4515d18bc..4549ae5d4 100644
--- a/pydantic_ai_slim/pydantic_ai/_agent_graph.py
+++ b/pydantic_ai_slim/pydantic_ai/_agent_graph.py
@@ -21,6 +21,7 @@
 from .output import OutputDataT, OutputSpec
 from .settings import ModelSettings, merge_model_settings
 from .tools import RunContext, Tool, ToolDefinition, ToolsPrepareFunc
+import functools
 
 if TYPE_CHECKING:
     from .mcp import MCPServer
@@ -617,7 +618,7 @@ def multi_modal_content_identifier(identifier: str | bytes) -> str:
     """Generate stable identifier for multi-modal content to help LLM in finding a specific file in tool call responses."""
     if isinstance(identifier, str):
         identifier = identifier.encode('utf-8')
-    return hashlib.sha1(identifier).hexdigest()[:6]
+    return _multi_modal_content_identifier_cached(identifier)
 
 
 async def process_function_tools(  # noqa C901
@@ -977,3 +978,9 @@ async def _process_message_history(
                 sync_processor = cast(_HistoryProcessorSync, processor)
                 messages = await run_in_executor(sync_processor, messages)
     return messages
+
+
+@functools.lru_cache(maxsize=4096)
+def _multi_modal_content_identifier_cached(identifier_bytes: bytes) -> str:
+    # Get the first 3 bytes (6 hex chars) directly
+    return hashlib.sha1(identifier_bytes).digest()[:3].hex()