The System Team in SAFe is a specialized Agile team that supports the ART by providing system-level integration, testing, and deployment infrastructure. Their primary responsibilities include:
End-to-end system testing (C)
Building and maintaining a production-equivalent staging environment (D) Deploying to staging (E) Defining Solution architecture (A) is the responsibility of Solution/System Architects. Creating new automated test scenarios (B) is typically a responsibility of the Agile Teams themselves.
"The System Team assists in building and maintaining development, test, and staging environments, performing end-to-end system integration and testing, and deploying to these environments." (Source: SAFe 6.0 Framework: System Team; SPC 6.0 Guide "Building Solutions with Agile Product Delivery")