diff --git a/src/langgraph/model/provider_chat_model.cpp b/src/langgraph/model/provider_chat_model.cpp
index 9ec1220..065be00 100644
--- a/src/langgraph/model/provider_chat_model.cpp
+++ b/src/langgraph/model/provider_chat_model.cpp
@@ -82,6 +82,7 @@ void inferTotalTokens(TokenUsage& usage) noexcept
         return {};
 
     UsageMetadata usage;
+    usage.tokens_.details_ = nlohmann::json::object();
     usage.source_ = UsageMetadataSource::Provider;
     usage.provider_ = std::string(chatProviderName(provider));
     usage.model_ = std::string(model);