Long-Term Support (LTS) 

A long‑term support (LTS) version of a software product delivers a very stable release that receives only essential fixes over an extended period, without adding new features. It’s intended for users who are happy with the current functionality and value maximum reliability over adopting the latest feature updates.

Improvements and fixes: 

Version 25.87 (06.03.2026) 

• A rare List index out of bounds error occured when the RE Model Builder is used with a complex configuration. Fixed.
• Import from Essential Macleod files now works correctly even when extended characters (such as ü, ä, ö) are used in file names.
• Import from other OTF projects improved: You can now change the sort order and apply filters by clicking the column captions.
• mm units have been added to indicate that substrate thickness must be specified in millimeters.
• Fitting plots were not visible when only Psi ellipsometric data were loaded. Fixed. 
• Deep Search Needle displayed the candidate insertion‑point coordinate in µm on the status bar, regardless of the current length‑unit settings. Fixed.

Version 25.86 (31.01.2026) 

• Secondary axis was not visible in multi‑coating mode. Fixed.
• The Specification section was disappearing from the Environment panel after using multi‑coating mode. Fixed.
• Computations with FlexiLayer and GradiLayer improved.
• Layer Characterization tab was not visible in the simplified ribbon view. Fixed.
• Incorrect icons were displayed for the Insert Above and Insert Below options on the Values panel. Fixed.
• The Cone Integration grid entry field was too narrow; the width has been increased.
• The In‑Memory Design Editor (if it is opened) now updates current layer thicknesses during optimization.
• Target Editor (complex configurations, switching between angular and spectral modes in the target) has been improved; configuration issues fixed. 
• Stress Target performed thickness units conversion even if Custom mode was used.  Fixed. In the Custom mode, units are alvays arbitrary units.
• The chromaticity color diagram did not display wavelengths corresponding to spectral lines in some cases, when the theme was changed from light to dark and vice versa.
• Fitting plots preserve the Y-axis scaling settings between OTF Studio sessions.
• X-axis title for the statistical output was not consistent for units different from nm. Fixed.
• In-Memory Design Editor problem set layer thicknesses to 0 after clicking Apply several times. Fixed.
• Column Editor issue fixed: when the Transform mode was used together with the selection Odd, Even, etc., the remaining values were set to zero. 
• The Target Editor in Angular mode did not update the incorporated Preview plot after changing the data. Fixed.
• When second Y-Axis was removed and then added with different curve types, the set of plots in the right configuration panel was incorrect. Fixed.
• Several drop-down lists had repeated Load tabs without explaining the specific action. Fixed.
• Very rare issue fixed in the Angular mode of the Target Editor. It happened in rare situations when a new target was immediately switched to Angular mode, and the Apply was clicked.
• IGU-related calculations in RE mode are consistent with the loaded design and model. Fixed a small inconsistency in R_outer calculations.