Developers are actively deploying a critical fix addressing a major performance bug that has caused significant slowdowns and excessive resource consumption in numerous popular applications running on Apple's latest operating system, macOS Tahoe (version 26). The issue, which surfaced shortly after macOS Tahoe's release on September 15, 2025, primarily affected apps built using the Electron framework, leading to frustrating user experiences characterized by sluggish performance and increased device temperatures.^[1][2][3] ### The Unexpected Toll of a Private API The root of the widespread slowdowns has been identified as an unforeseen interaction between macOS Tahoe and a specific private Apple API, known as `cornerMask`, previously utilized by the Electron framework. Electron, a popular tool for building cross-platform desktop applications, allows developers to package web technologies into native app experiences. Many widely used applications, including Discord, Slack, Figma, and Visual Studio Code, rely on Electron.^[1][2] Following the release of macOS 26 Tahoe last month, users began reporting that these Electron-based applications exhibited unusually high GPU usage, even when idle. This excessive GPU demand not only led to noticeable slowdowns and lag but also caused Mac devices to run hotter and trigger constant fan activity.^[1][2] Private APIs are typically intended for Apple's internal use and are not officially supported for third-party developers, making their use inherently risky. The change implemented in macOS Tahoe apparently broke the compatibility of this particular private API, leading to the observed performance degradation across a broad spectrum of applications.^[1][2] ### The Fix and Its Rapid Rollout Responding swiftly to the reported issues, the Electron development team addressed the problem by removing the problematic `cornerMask` API from newer versions of their framework. This crucial update restores normal GPU behavior and mitigates the performance issues previously experienced on macOS Tahoe.^[2] The fix is now being rolled out by individual application developers who are updating their Electron-based apps to incorporate the corrected framework. This staggered deployment means that while some applications have already seen significant improvements, others are still in the process of updating. Key facts about the fix and rollout: * **Cause Identified:** The issue stemmed from Electron apps' use of the private `cornerMask` API, which became incompatible with changes in macOS Tahoe.^[1][2] * **Electron Update:** Newer versions of the Electron framework no longer utilize this problematic API.^[1][2] * **Developer Action:** Third-party app developers are integrating these updated Electron versions into their applications.^[1][2] * **Progress Tracking:** An open tracker, "ShameElectron," is helping users monitor which popular apps have already implemented the fix.^[1][2] Many prominent applications have already pushed updates to resolve the slowdowns, including: * Claude^[1][2] * Discord^[1][2] * Docker Desktop^[1][2] * Figma^[1][2] * GitHub Desktop^[1][2] * MongoDB Compass^[1] * Notion^[1][2] * Obsidian^[1][2] * Pocket Casts^[1][2] * Signal^[1][2] * Slack^[1][2] * Super Productivity^[1] * Visual Studio Code^[1][2] However, some major Electron-based applications, such as 1Password, Bitwarden, Cursor, Dropbox, and Windsurf, have yet to release updates incorporating the fix, meaning users of these apps may still experience performance issues.^[1][2] ### User Impact and Ongoing Improvements For users experiencing persistent slowdowns, the primary recommendation is to ensure all Electron-based applications are updated to their latest versions. Users can typically check for app updates within the application itself or through the Mac App Store. If an app has not yet received an update, temporarily quitting it or using its web-based counterpart may alleviate performance issues.^[2] Apple itself has also been working on broader performance improvements. The macOS Tahoe 26.1 public beta 2, released on October 7, 2025, is expected to bring general performance enhancements and bug fixes to the operating system.^[4] This follows macOS Tahoe 26.0.1, which was released on September 29, 2025, addressing various issues, including an update problem for M3 Ultra Mac Studio machines.^[3][5] While Apple acknowledges that minor dips in performance can occur temporarily after any major software update due to background tasks like re-indexing, the severity of the Electron bug necessitated direct action from app developers.^[6][7] The swift response from the Electron team and individual developers highlights the collaborative effort required to maintain a seamless user experience across a complex software ecosystem. As more applications integrate the necessary updates, Mac users can expect their macOS Tahoe experience to return to optimal performance, ensuring their devices run efficiently and reliably.