At its Google Cloud Next conference in San Francisco today, Google announced the launch of a new discounting system for its Google Cloud Platform public cloud offering. Customers will be able to get a lower cost after committing to a particular volume.

That model is different from the reserved instances available from public cloud market leader Amazon Web Services (AWS). And it’s in addition to the sustained-use discounts, per-minute pricing, and preemptible virtual machines (VMs) that Google has offered for the past few years. AWS says its reserved instances cost up to 75 percent less than regular on-demand instances.

But with Google’s system, customers will be able to change the types of VMs they’re running.

Going this way can cut monthly bills by 57 percent, with no upfront payment, said Urs Hölzle, senior vice president of technical infrastructure.

“You’re not facing a huge unit cost cliff when you exceed your forecast,” Hölzle said, “because we believe that when you move to the cloud, capacity planning and cost planning should really become a distant memory and not your No. 1 headache — no spreadsheets, no Ph.D. in economics needed to manage it all.”

Cloud management startup RightScale has analyzed Google’s committed-use discounts and AWS’ reserved instances and has found that Google’s system will be cheaper.

In September AWS introduced convertible reserved instances, which allow customers to change instance types. But they’re only available in three-year terms, while Google’s system requires monthly payments. A blog post has more detail.

Update at 10:20 a.m. Pacific: Added comment from RightScale.

Update at 2:18 p.m. Pacific: Added information on AWS convertible reserved instances.