diff --git a/CHANGELOG.md b/CHANGELOG.md
index 40e806916..7769f776d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -66,6 +66,7 @@ to include examples, links to docs, or any other relevant information.
   retried on its configured interval instead.
 - Nexus-context workflow/activity starts no longer set `on_conflict_options` when there are no links
   or callbacks to attach.
+- The workflow sandbox now passes `pydantic_core` through by default, alongside `pydantic`.
 
 ### Security
 
diff --git a/temporalio/worker/workflow_sandbox/_restrictions.py b/temporalio/worker/workflow_sandbox/_restrictions.py
index 23774fcd2..3e6e0d6ba 100644
--- a/temporalio/worker/workflow_sandbox/_restrictions.py
+++ b/temporalio/worker/workflow_sandbox/_restrictions.py
@@ -513,6 +513,8 @@ def with_child_unrestricted(self, *child_path: str) -> SandboxMatcher:
         # Due to how Pydantic is importing lazily inside of some classes, we choose
         # to always pass it through
         "pydantic",
+        # Same for its compiled core, which Pydantic-based libraries import lazily
+        "pydantic_core",
     }
 )
 
diff --git a/tests/contrib/openai_agents/test_openai_replay.py b/tests/contrib/openai_agents/test_openai_replay.py
index 6db463392..7c9a586b2 100644
--- a/tests/contrib/openai_agents/test_openai_replay.py
+++ b/tests/contrib/openai_agents/test_openai_replay.py
@@ -1,3 +1,4 @@
+import warnings
 from pathlib import Path
 
 import pytest
@@ -32,6 +33,10 @@ async def test_replay(file_name: str) -> None:
     with (Path(__file__).with_name("histories") / file_name).open("r") as f:
         history_json = f.read()
 
+    with warnings.catch_warnings(record=True) as recorder:
+        warnings.filterwarnings(
+            "always", message=r"Module .* was imported after initial workflow load"
+        )
         await Replayer(
             workflows=[
                 ResearchWorkflow,
@@ -44,3 +49,10 @@ async def test_replay(file_name: str) -> None:
             ],
             plugins=[OpenAIAgentsPlugin()],
         ).replay_workflow(WorkflowHistory.from_json("fake", history_json))
+
+    # Sandbox imports during an activation count toward the deadlock timeout
+    assert not [
+        str(w.message)
+        for w in recorder
+        if "was imported after initial workflow load" in str(w.message)
+    ]