There are various potential improvements we could make to our CI matrix to improve test coverage of critical components while reducing the overall load. Some possible improvements that have been suggested at various times include:

• Reducing the frequency of testing multiple Python versions to nightly: We very rarely encounter cases where our CI tests uncover a bug that is only present in one Python version. While it is possible, we don't generally use cutting edge language or standard library features that require a very new version of Python. We could choose to only test the oldest supported Python version in PR CI and only run the other tests in nightlies.
• Don't test arm builds all the time: Architecture-specific bugs are similarly rare and we probably don't need to test both x86 and arm on every PR and in CI.
• Better testing of CUDA drivers: Currently we only test the oldest and newest supported drivers between both PR and nightly CI. However, for use cases like JIT-compiled kernels we may, at minimum, want to test the oldest and newest supported drivers for each major version of CUDA that we support.
• Reduce duplication between wheel and conda testing: We currently run a matrix of both wheel and conda tests. We may be able to use a subset of those as long as we get coverage of both wheels and conda (and coverage of all the other pieces -- Python version, CUDA verison, etc -- between the wheel and conda tests).
• Only run a subset of test jobs on a PR based on which files were modified.