Avid today released Sibelius 2018.5 to fix an issue in Sibelius where running some plug-ins would cause a memory leak that slowed Sibelius down until you restarted it. This most notably affected the Dolet MusicXML export plug-in, and only on Windows, not on Mac.
Today Avid released Sibelius 2018.4.1, a maintenance release to the substantial 2018.4 release from earlier this month. A few bugs hitched their way along for the ride on that release, and those have now been fixed in the latest update.
Today Avid released Sibelius 2018.4, a broad release with many new features and some longstanding requests addressed. Areas of improvement include multi-edits for text, a new note spacing rule affecting multiple voices and other cases, deleting and adding bars at the beginning of the score, smarter ties, and many more other enhancements. Avid also announced a new naming strategy where the pro-level version is now called “Sibelius Ultimate”.