Understanding the new ISA circuits requirement

After a recent change to the Qiskit Runtime primitives, you might see a new error message when submitting circuits to a backend: Failed - Circuits do not match the target definition (non-ISA circuits). The error message then lists a few suggestions to resolve the issue, but it doesn’t entirely explain what’s going on. So, what exactly is happening here?

In a recent post on the IBM Quantum blog, we detail why the newest version of Qiskit Runtime requires that all circuits submitted to a backend must conform to the constraints of the backend’s Target. Such circuits are considered to be written in terms of that backend’s Instruction Set Architecture (ISA) — i.e., the set of instructions the device can understand and execute. These Target constraints include the device’s native basis gates, its qubit connectivity, and - when relevant - its pulse and other instruction timing specifications. The blog post offers some quick and easy solutions for anyone running into this new ISA circuits error message, and explains the reasoning behind the change.