The 99.99% availability configuration requires four connections across two GCP regions. For more information, see the configuration for Dedicated Interconnect or Partner Interconnect:
Topology for Production-level Applications Overview
For mission-critical applications that have a low tolerance for downtime, Google recommends that you use the 99.99% available configuration. To be covered under the production-level applications SLA (99.99% monthly uptime percentage), you must build your network according to this topology.