Discrepancies in calculated results on Windows 11 24H2

The issue

The QA team at GraphPad Prism identified small but consistent discrepancies in computed values when running certain analyses, especially Nonlinear regression and other curve-fitting models, on systems with the Windows 11 24H2 update.  Prism depends on precise numerical calculations, so even subtle changes in how numerical operations behave, such as changes introduced in the latest system update, can sometimes lead to noticeable differences in results.

We investigated the issue more deeply, and found similar reports from other developers of other applications. After updating to Windows 11 24H2, some users have observed differences in numerical results compared to previous Windows versions, even when using the same hardware and binaries. The issue has been reported to Microsoft, and discussions are ongoing within the developer community.

FAQs

Why are there discrepancies in my Prism results after updating to Windows 11 24H2?

It seems that  Windows 11 24H2 may include changes in system libraries that could affect how numerical operations are carried out on certain processor architectures. While the exact technical details haven’t been fully clarified, these changes can lead to small numerical differences in certain types of analyses.

Is this a bug in Prism?

This is not a bug in the Prism software itself. Nothing has changed in Prism's code that has caused the observed discrepancies. The core algorithms and calculation logic in Prism remain unchanged. This behavior appears to stem from external changes in the system libraries introduced in Windows 11 24H2.

Will this issue be fixed in a future release?

This issue seems to be related to changes introduced in the Windows 11 24H2 update that affect how some numerical operations behave at runtime. While the exact cause is not fully confirmed, it may involve updates to system libraries that are outside of Prism’s control. We are actively monitoring the situation and staying in close contact with platform and development communities. We will do everything that depends on us to minimize the impact on Prism users and ensure consistent results across supported environments. If any adjustments on our side become feasible or necessary, they will be considered for a future release.

Are the discrepancies significant?

The differences are generally trivial and within the expected bounds of numerical precision. However, results of some unstable or ambiguous nonlinear regression models may show noticeable variation due to their sensitivity. Note, however, that these results are inherently "unstable" or "ambiguous" and as a result, the specific values should not be considered reliable estimates. Discrepancies in these "unstable" or "ambiguous" results - no matter how large - do not change the overall interpretation of the results: that they are not reliable estimates.

Should I trust the results I observe after updating to Windows 11 24H2?

In most cases, yes. The differences introduced by the update are typically very small and only affect models that are sensitive to tiny numerical variations, such as non-linear regression. If your model is well-behaved and stable, the results are still reliable. However, for ambiguous or unstable model fits, small changes may lead to slightly different outcomes. However, as noted above, these unstable/ambiguous results should not be interpreted as reliable estimates anyway. Any discrepancies - regardless of their size - would not change this interpretation.

Can I revert to previous results?

After updating to Windows 11 24H2, changes in Prism results will appear after recalculation of the analysis. If you saved your Prism files or exported results before updating to Windows 11 24H2, you can refer back to those for comparison. You can also freeze the results of specific analyses to preserve them from recalculation. Alternatively, running the same analysis on a system with an earlier version of Windows should reproduce the previous results.

Does this issue occur on earlier versions of Windows 11?

These discrepancies have only been observed on systems running Windows 11 24H2. The issue appears in this update and has not been reported on earlier versions of Windows.