# QCS QPU Gateway

The QCS Gateway is a service that provides high-availability, 24/7 connectivity to a QPU, even when that QPU is undergoing maintenance. This provides a seamless user experience, especially when using [on-demand access](https://docs.rigetti.com/qcs/guides/access-a-qpu/on-demand-access). If the QPU is undergoing maintenance, your job will be queued until it is available and then run at the first opportunity.

|                             | Direct Access                                                                                                                            | QCS Gateway                                  |
| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------- |
| **When should you use it?** | When you have a QPU reservation, strict latency requirements, and direct network access                                                  | All other times                              |
| Connection Routing          | Direct connection to the QPU                                                                                                             | Routes requests to QPUs                      |
| Network Access              | <p>Requires direct network access to Rigetti Lab<br>(e.g. from QCS JupyterHub)</p>                                                       | Accessible from more network locations       |
| Request Latency             | Minimum possible                                                                                                                         | Small (< 1ms) additional request latency     |
| Availability                | Not highly available; connection fails during service upgrade and maintenance. Uptime is only guaranteed during user reservation periods | Highly available; jobs may be submitted 24/7 |

###