diff --git a/pyproject.toml b/pyproject.toml
index b46e17e..3996cb9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -40,7 +40,7 @@ dev = [
     "langchain-acp[deepagents]",
     "python-dotenv",
     "pydantic-acp",
-    "pydantic-ai-harness[code-mode]==0.52.0",
+    "pydantic-ai-harness[code-mode]==0.55.0",
     "pydantic-ai-slim>=2.9.0,<=2.52.0",
     "pydantic-graph",
     "pydantic>=2.7",