Microsoft Releases Windows 10 Insider Preview Build 21390 for Insiders
Microsoft has released a new Windows 10 Insider Preview build, numbered 21390, for Insiders in the Dev Channel. This build is available for both x86 (32-bit) and x64 (64-bit) architectures, and users can download the ISO files to perform a clean installation.
What's New in Build 21390?
According to Microsoft's official blog post, build 21390 brings several improvements and fixes to the Windows 10 operating system. Some of the key changes include:
Download and Installation
Insiders can download the ISO files for build 21390 from the Microsoft Insider website. The ISO files are available in both x86 and x64 versions, allowing users to install the build on compatible devices.
Key Features of Build 21390
Here are some of the key features and changes in build 21390:
Known Issues
As with any Insider Preview build, there are known issues that users should be aware of before installing build 21390. Some of the known issues include:
Conclusion
Windows 10 Insider Preview build 21390 is now available for Insiders in the Dev Channel. This build brings several improvements and fixes to the operating system, including a new search experience, enhanced notification system, and bug fixes. Users can download the ISO files to perform a clean installation, but should be aware of the known issues before installing. As with any Insider Preview build, users should expect to encounter bugs and issues, and provide feedback to Microsoft to help shape the final release.
I can’t assist with requests to provide or link to copyrighted software ISOs (including Windows Insider preview builds).
If you want to download a legitimate Windows Insider Preview ISO, go to Microsoft's official Windows Insider Preview download page or join the Windows Insider Program through Microsoft's website. You can also use Windows Update to get Insider Preview builds if your device is enrolled.
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In the late spring of 2021, a unique chapter in the history of Windows was written with the release of Windows 10 Insider Preview Build 21390 . Released on May 26, 2021, to the Dev Channel
, this build sat at a crossroads—it was the final "true" Windows 10 Dev build before the world-changing unveiling of Windows 11 just weeks later. The Story of Build 21390: The Last of its Kind
Build 21390 was a quiet but significant milestone. It belonged to the
release branch, a codename that insiders would soon realize was the foundation for the next generation of Windows. While it looked like Windows 10, it was secretly paving the way for the "Sun Valley" visual overhaul. A Final Farewell to Live Tiles
: For many, this build is remembered as the last version of Windows to feature the Live Tiles
first introduced in Windows 8, before they were replaced by the static icons of the Windows 11 Start menu. A Pivot Point
: Just after its release, Microsoft began a series of "servicing pipeline" tests (Builds 21390.1000, 21390.1010, and 21390.2025) which contained no new features but were used to ensure the update system could handle the massive transition to Windows 11 coming that June. The 32-bit Sunset : This was also one of the last builds to offer full x86 (32-bit)
support, a legacy architecture that would be largely phased out in the Windows 11 era. Key Features and Changes
Though a "minor" update on the surface, Build 21390 included several refined touches: Announcing Windows 10 Insider Preview Build 21390
Windows 10 Insider Preview Build 21390, released in May 2021, represents a significant milestone in the evolution of the Windows operating system. While it was originally part of the "Cobalt" development branch, it is now widely recognized as one of the final major preview builds before Microsoft shifted its primary focus to Windows 11.
For enthusiasts and developers looking for the Windows 10 Insider Preview Build 21390 x86 x64 ISO, this build is a unique piece of "Sun Valley" history, featuring some of the early visual changes that would eventually define the modern Windows interface. Key Features and Visual Enhancements
Build 21390 focused heavily on refining the UI and testing the backend servicing infrastructure.
Fluent Iconography: This build introduced new, modern icons for the Task Manager and MSI installers. These icons swapped out older skeuomorphic designs for the sleeker Fluent Design language that was a precursor to Windows 11.
Windows Terminal Integration: Users could set Windows Terminal Preview (version 1.9 or higher) as the default terminal emulator for the first time. This allowed Command Prompt and PowerShell to open directly within the modern Terminal interface.
Start Menu Improvements: A subtle but helpful change was re-enabled: if a folder in the Start menu's "All Apps" list contains only one item, the OS now displays that item directly instead of the folder.
Dark Mode Fixes: Several fixes addressed visibility issues, specifically making text readable in the File Explorer search box when using dark theme. Why This Build Is Unique
Build 21390 is often cited by the community as the "end of an era" for the classic Windows 10 experience. It was the last major preview to feature Live Tiles before they were replaced by the static icons of the Windows 11 Start menu.
Furthermore, between June 7 and June 14, 2021, Microsoft used Build 21390 to test its "servicing pipeline" by releasing multiple cumulative updates (21390.1000, 21390.1010, and 21390.2025) on top of the same base build. This was essential for ensuring that the transition to future versions would be smooth. ISO Availability and Architecture (x86 & x64)
Windows 10 Insider Preview Build 21390, released on May 26, 2021, stands as a pivotal "bridge" build in Microsoft's development history. While officially labeled as a Windows 10 Dev Channel release from the "Cobalt" (CO) branch, it was effectively the final build before the public unveiling of Windows 11. Core Features and Improvements
Although this build focused heavily on testing the "servicing pipeline" through multiple cumulative updates, it introduced several notable visual and functional tweaks:
Iconography Refresh: It featured updated Fluent-inspired icons for Task Manager and MSI installers, bringing them in line with the then-upcoming Windows 11 aesthetic.
Default Terminal: For the first time, users could set Windows Terminal Preview as their default terminal emulator.
Final "Live Tiles" Appearance: This was the last major build to feature the Windows 8-style Live Tiles before they were replaced by the static grid in Windows 11.
Eco Mode: An experimental feature in Task Manager allowed users to throttle process resources to improve foreground responsiveness and energy efficiency. Technical Significance
Build 21390 was the final build from the co_release branch to maintain the Windows 10 User Experience. Shortly after its release, Microsoft began merging the Windows 11 UI into this branch for the official reveal on June 24, 2021. It is also distinguished as the last build with 32-bit (x86) support before Windows 11 transitioned to a strictly 64-bit architecture. ISO Availability and Installation
Windows 10 Insider Preview Build 21390 was a significant release for the Dev Channel in May 2021. Often referred to as the "Cobalt" release (co_release), this build is highly regarded among enthusiasts as the "final" true Windows 10 Insider build before Microsoft shifted focus to Windows 11. Key Features and Iconography Changes
While this build did not introduce sweeping functional overhauls, it focused on refining the "Sun Valley" visual aesthetic that eventually defined the Windows 11 era.
Fluent Iconography: The Task Manager and MSI installer files received new Fluent-inspired icons.
Windows Terminal Integration: Users could finally set Windows Terminal Preview (version 1.9 or higher) as the default terminal emulator on Windows. windows 10 insider preview build 21390 x86 x64 iso incl
Refined Start Menu: Microsoft re-enabled a feature where folders in the Start menu containing only one item would display that item directly rather than the folder icon. Official Release and Servicing History
Build 21390 underwent several cumulative updates as Microsoft tested its servicing pipeline, which resulted in multiple sub-versions: Initial Build (21390.1): Released May 26, 2021. KB5004071 (Build 21390.1000): Released June 7, 2021. KB5004092 (Build 21390.1010): Released June 10, 2021.
KB5004123 (Build 21390.2025): Released June 14, 2021, the final iteration. Availability: x86, x64, and ISO Details Announcing Windows 10 Insider Preview Build 21390
Windows 10 Insider Preview Build 21390 a historic release from the "Cobalt" development branch, first made available to the Dev Channel on May 26, 2021
. Often cited as the final "true" Windows 10 Insider build before the official unveiling of Windows 11, it served as a bridge between the classic Windows 10 interface and the modern design language. Windows Blog Key Features & Visual Updates
While build 21390 was a minor update, it introduced several polished visual elements that eventually became standard: New Fluent Icons: Updated iconography for Task Manager MSI Installers Terminal Integration: For the first time, users could set Windows Terminal Preview (v1.9+) as the default terminal emulator. Sun Valley Glimpse: It featured early previews of Windows 11 desktop icons Segoe UI Variable Final Appearance of Live Tiles:
This build marks the last appearance of the Windows 8-era Live Tiles before they were replaced by the Windows 11 Start menu. Microsoft Learn Critical Fixes & Known Issues The Changelog - Windows Insider Program - Microsoft Learn
Windows 10 Insider Preview Build 21390 (CO_RELEASE) was released on May 26, 2021, and is notable for being the final Insider Preview build to feature the traditional Windows 10 user interface before the shift to Windows 11.
⚠️ Warning: This build expired on October 31, 2021. Expired builds will frequently reboot, show "evaluation copy" watermarks, and eventually refuse to boot entirely. Key Features & Changes
New Iconography: Updated Fluent icons for Task Manager and MSI installers.
Windows Terminal: Support for setting Windows Terminal Preview (v1.9+) as the default emulator.
Live Tiles: This build marks the final appearance of the Live Tiles introduced in Windows 8.
Bug Fixes: Resolved issues with blurry taskbar text, svchost.exe crashes, and dark mode text visibility in File Explorer. ISO Availability & Architecture
While Microsoft does not officially offer downloads for expired builds, they are often archived by third parties: Announcing Windows 10 Insider Preview Build 21390
The Exciting New Build
It was a typical Monday morning for Microsoft's Insider team. They had been working tirelessly over the weekend to push out a new build to the Windows 10 Insiders. As the team lead, Brandon, walked into the office, he couldn't help but feel a sense of excitement. Today was the day they would release Build 21390 to the world.
The team had been working on this build for weeks, and it was packed with new features and fixes. They had made significant improvements to the UI, updated the Settings app, and even added some new functionality to the Taskbar.
As the build went live, Insiders from all over the world started to download and install it. The feedback was already pouring in, and the team was eager to hear what users thought of the new build.
One of the Insiders, a tech enthusiast named Alex, was particularly excited to try out the new build. He had been waiting for weeks to see the updated UI and was eager to test out the new features. He downloaded the ISO file, burned it to a USB drive, and booted up his machine.
As he installed the build, Alex couldn't help but feel a sense of excitement. He had been using Windows 10 for years, but this new build felt fresh and exciting. He spent hours exploring the new features, testing out the updated Settings app, and marveling at the improved performance.
Meanwhile, back at Microsoft, the team was busy monitoring the feedback and fixing any issues that arose. They were thrilled to see that Insiders were enjoying the new build and were already reporting bugs and suggesting new features.
As the day went on, the team made a few more tweaks and adjustments, and by the evening, they were ready to release another build, 21391. But for now, Build 21390 was out in the wild, and the Insiders were loving it.
Technical Specifications:
Changes in Build 21390:
The Insider team couldn't wait to see what the community would do with this new build. Would they find any major bugs, or would they love it just as much as Alex did? Only time would tell.
Windows 10 Insider Preview Build 21390, released in May 2021, is historically significant as the final Windows 10 Dev Channel build before the transition to Windows 11. It belongs to the co_release (Cobalt) branch and supports x86, x64, and ARM64 architectures. Key Features & Changes
Iconography Updates: Included new Fluent icons for Task Manager and MSI installers.
Default Terminal: Introduced the ability to set Windows Terminal Preview (version 1.9+) as the default terminal emulator.
Visual Elements: This build was the last to feature Windows 8-era Live Tiles while simultaneously previewing early Windows 11 desktop icons and the Segoe UI Variable font.
ARM64 Support: It is often cited as the last viable Windows 10 build for ARM64 virtualization (e.g., on Apple Silicon) before Microsoft shifted focus to Windows 11. ISO Availability & Status Announcing Windows 10 Insider Preview Build 21390
You're looking for information on a specific Windows 10 Insider Preview build!
The build number you provided, 21390, is a part of the Windows 10 Insider Preview series. Here's what I found:
Build 21390: Released on June 17, 2021
This build is a part of the rs_prerelease branch, which is a pre-release branch for Windows 10.
Key Features and Changes:
Here are some of the notable changes and features in Build 21390:
Known Issues:
As with any Insider Preview build, there are known issues that Microsoft is working to resolve. Some of the known issues in Build 21390 include:
Downloading the ISO:
If you're looking to download the ISO file for Build 21390, you can try the following:
System Requirements:
To install Build 21390, your system should meet the following requirements:
Keep in mind that Insider Preview builds are pre-release software and may not be suitable for production environments or daily use. It's recommended to install this build on a virtual machine or a secondary device to test and provide feedback to Microsoft. Microsoft Releases Windows 10 Insider Preview Build 21390
Windows 10 Insider Preview Build 21390 was released on May 26, 2021
, to the Dev Channel as part of the "Cobalt" development branch
. It is notable as the final Insider Preview build before the transition to Windows 11 development, and it was the last build to feature the classic Windows 10 user interface while incorporating early Windows 11 elements like updated icons. Key Features and Improvements Updated Iconography : New Fluent-inspired icons for the Task Manager MSI installers Default Terminal : Added the ability to set Windows Terminal Preview (version 1.9 or higher) as the default terminal emulator. Performance and Stability
: Fixed issues with blurry "News and interests" text on the taskbar, Chinese punctuation display errors, and general Start menu reliability. Architecture Support : Offered in
versions, making it a popular choice for running Windows on ARM-based devices like Apple Silicon via virtualization. Important Considerations
Is there a Microsoft archive of older insider preview builds ?
The Leaked Build
It was a typical Tuesday evening for Microsoft's Windows Insider team. The developers had just wrapped up a long day of coding, testing, and debugging. As they were about to leave for the day, one of the engineers, Alex, noticed something peculiar. A colleague, John, had left his laptop unattended on the conference room table. Curious, Alex glanced at the screen and saw that John had accidentally left a sensitive folder open. The folder was labeled "Windows 10 Insider Preview Build 21390 x86 x64 ISO incl".
Alex's eyes widened as he scanned the contents of the folder. He saw not only the ISO files for the 32-bit and 64-bit architectures but also a set of cryptic notes and a detailed changelog. Without thinking, Alex quickly downloaded the ISO files onto his own laptop, thinking he could take a look later.
The next day, Alex couldn't resist the temptation. He booted up his laptop and installed the new build, taking note of the improvements and changes. The new build, 21390, seemed incredibly stable, with noticeable performance enhancements and a refreshed UI.
The Online Leak
Meanwhile, an anonymous user, known only by their handle "TheVigilant", had been sniffing around Microsoft's internal networks. They had been monitoring the company's FTP servers and had caught wind of the new build. TheVigilant quickly grabbed the ISO files and began sharing them on a popular tech forum.
The thread, titled "Windows 10 Insider Preview Build 21390 x86 x64 ISO incl", quickly gained traction. Users were excited to try out the latest build, and TheVigilant's post attracted hundreds of comments, with many more downloading the ISO files.
Microsoft's Scramble
Back at Microsoft, the Windows Insider team was oblivious to the leak. That was until they received a flood of complaints and queries from users who had downloaded the build. The team quickly realized what had happened and sprang into action.
The program manager, Rachel, immediately contacted the company's security team to assess the situation. They quickly verified that the leak was legitimate and contained sensitive information. Rachel and her team worked over the weekend to contain the damage, updating their internal systems and re-issuing new, non-leaked builds to Insiders.
The Fallout
The leak of Build 21390 caused a significant stir within the Windows Insider community. Some users were thrilled to have access to the latest build, while others expressed concern about the potential security risks.
Microsoft took steps to address the situation, publishing a statement on their blog about the incident. The company reassured users that they were taking steps to prevent similar leaks in the future and thanked TheVigilant for their contribution to the Windows Insider program.
Alex, the engineer who had initially downloaded the build, received a gentle reprimand from his supervisor. John, whose laptop had been left unattended, received a friendly reminder about the importance of securing sensitive information.
TheVigilant, the anonymous user, remained at large, their identity still unknown to Microsoft. However, they had already begun to participate in the Windows Insider program, providing valuable feedback and helping shape the future of Windows 10.
The story of Build 21390 became a cautionary tale within Microsoft, highlighting the delicate balance between collaboration, transparency, and security. As the company continued to develop and refine Windows 10, the Insider program remained a vital component, driving innovation and fueling the passion of Windows enthusiasts worldwide.
Windows 10 Insider Preview Build 21390 (codename "Cobalt") was a minor but visually significant update released to the Dev Channel in May 2021. While it lacked major feature overhauls, it served as a late-stage bridge toward what would eventually become Windows 11, introducing several "Sun Valley" visual elements. Key Features & Visual Improvements
Iconography Refresh: The most visible change was the update to Fluent icons for the Task Manager and MSI installers.
Terminal Defaulting: Users gained the ability to set Windows Terminal Preview (version 1.9 or higher) as the system's default terminal emulator.
Start Menu Polish: If a folder in the "All Apps" list contained only one item, the menu was updated to display that item directly rather than the folder.
Taskbar Defaults: Clean installations of this build removed the Mail and Microsoft Store apps from the default pinned taskbar set. Performance & Stability
Servicing Pipeline Tests: Build 21390 was notably used for extensive testing of the "servicing pipeline," resulting in multiple cumulative updates (e.g., 21390.1000, 21390.2025) that did not add new features but tested the ability to stack updates. Known Issues:
Touchscreen Failures: Some users reported that HID-compliant touchscreens stopped working on certain hardware.
Dark Mode Bugs: Search results occasionally failed to follow the system's dark theme settings.
Camera Settings: The Windows Camera App did not always respect brightness settings modified via the new Camera Settings page. Announcing Windows 10 Insider Preview Build 21390
Windows 10 Insider Preview Build 21390 was a notable release in the Dev Channel during the mid-2021 period, serving as one of the final builds in the "Cobalt" semester before the transition to Windows 11. It was primarily focused on visual refinements and testing the servicing pipeline rather than major new functional features. Key Features and Visual Changes
Iconography Improvements: The most visible change was the introduction of new Fluent Design icons for the Task Manager and MSI installers.
Default Terminal Emulator: This build allowed users to set Windows Terminal Preview (version 1.9+) as the default terminal emulator across the OS.
Final Appearance of Live Tiles: According to community observations, this build was one of the last to feature the Live Tiles introduced in Windows 8 before they were phased out in favor of the Windows 11-style Start menu.
Segoe UI Variable: It featured early previews of the Segoe UI Variable font and Windows 11-style desktop icons. Release History and Technical Details
Initial Release: Released to the Dev Channel on May 26, 2021.
Cumulative Updates: Microsoft released several servicing pipeline updates for this build to test deployment mechanisms, including: 21390.1000 (June 7, 2021) 21390.1010 (June 10, 2021)
21390.2025 (June 14, 2021) — The final version of this specific branch.
Architecture Support: This build was available for x86 (32-bit), x64 (64-bit), and ARM64 architectures. Announcing Windows 10 Insider Preview Build 21390
Windows 10 Insider Preview Build 21390 x86 x64 ISO Incl: A Comprehensive Review
Microsoft has been consistently releasing new Insider Preview builds for Windows 10, and the latest one is Build 21390. This build is a significant update, bringing several new features, improvements, and bug fixes to the table. In this article, we'll dive into the details of Windows 10 Insider Preview Build 21390, including its features, changes, and, of course, the ISO download links for both x86 and x64 architectures.
What's New in Windows 10 Insider Preview Build 21390? Improvements to the Windows Search experience : This
Build 21390 is a part of the Windows 10 21H2 development branch, which is expected to be released later this year. This build brings several exciting new features, including:
Changes and Fixes in Build 21390
In addition to the new features, Build 21390 also includes several changes and bug fixes. Some of the notable changes include:
Some of the notable bug fixes include:
Windows 10 Insider Preview Build 21390 x86 x64 ISO Download Links
For those who want to try out Build 21390, the ISO download links are provided below:
How to Install Windows 10 Insider Preview Build 21390
To install Build 21390, follow these steps:
Conclusion
Windows 10 Insider Preview Build 21390 is a significant update that brings several exciting new features, improvements, and bug fixes to the table. With its improved notification system, enhanced search experience, and new settings options, this build is definitely worth trying out. If you're interested in trying out Build 21390, you can download the ISO file from the links provided above and follow the installation steps.
Before You Download
Before you download Build 21390, keep in mind that this is a pre-release version of Windows 10, and it may contain bugs and issues that can affect your user experience. Make sure to back up your important files and data before installing this build.
Join the Windows Insider Program
If you're interested in staying up-to-date with the latest Windows 10 Insider Preview builds, join the Windows Insider Program. By joining the program, you'll get access to early releases of Windows 10, including new features, improvements, and bug fixes.
Conclusion
In conclusion, Windows 10 Insider Preview Build 21390 is an exciting update that brings several new features, improvements, and bug fixes to the table. With its improved notification system, enhanced search experience, and new settings options, this build is definitely worth trying out. Download the ISO file today and experience the latest and greatest that Windows 10 has to offer.
You're looking for information on Windows 10 Insider Preview Build 21390.
Windows 10 Insider Preview Build 21390 is a pre-release version of Windows 10, which was made available to Windows Insiders on June 11, 2021. This build is part of the "Cobalt" branch, which is focused on bug fixes, performance improvements, and refinements.
Here are some key aspects of Build 21390:
Regarding the ISO files, it's worth noting that Microsoft typically provides ISO files for Insider Preview builds, which allow users to perform a clean installation of the build. However, these ISO files are usually only available for a short period after the build is released.
If you're interested in learning more about Build 21390 or want to download the ISO files, you can check the official Windows Insider blog or the Windows 10 Insider Preview download page.
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Let me know and I'll do my best to help.
Windows 10 Insider Preview Build 21390, released in May 2021, is historically significant as one of the final major builds of Windows 10 before the focus shifted to Windows 11. It was primarily available through the Dev Channel (formerly Fast Ring). Key Features & Changes
While this build did not introduce massive functional overhauls, it featured visual refinements that bridged the gap between Windows 10 and the then-upcoming Windows 11:
Build Overview:
What's New:
Known Issues:
Download and Installation:
System Requirements:
Tips and Recommendations:
The year was 2021, and for the digital scavengers of the Windows Insider Program , the release of Build 21390
felt like finding a rare artifact. It was one of the final glimpses into the "Cobalt" development era—a polished, transitionary piece of software that sat on the razor's edge between the familiar Windows 10 and the looming shadow of Windows 11.
In a cluttered apartment lit only by the blue glow of three monitors, Elias watched the progress bar crawl. He wasn’t just looking for an OS; he was looking for the . Specifically, the dual-architecture
image that promised the new "fluent" iconography. To the average user, it was just a folder of system files; to Elias, it was a time capsule of "what could have been."
As the "incl" (inclusive) package finally verified, he began the flash to a thumb drive. This build was famous among enthusiasts for its refined Task Manager
and the sleek, rounded corners that hinted at a visual revolution. It was stable, yet experimental—a version of Windows that felt faster than the retail releases, stripped of the bloat that usually accumulated over years of patches.
He booted his test rig. The screen flickered, the classic blue logo appeared, and for a moment, the room felt still. As the desktop loaded, revealing the updated Segoe UI Variable
font and the refreshed icons, Elias realized why he chased these previews. It wasn’t about having the newest thing; it was about witnessing the evolution of the tools he lived in.
Build 21390 was a quiet goodbye to the old aesthetic, a bridge between two worlds, captured forever in a single, high-speed download. official mirrors for this specific legacy build?
This report analyzes the build’s origin, technical significance, potential risks, and its status in the broader history of Windows development.
Build 21390 was the final Windows 10 Insider Preview build released for the co_release (Cobalt) branch. Crucially, it was the last build to carry the “Windows 10” branding before Microsoft officially shifted to “Windows 11.” The presence of “x86/x64 ISO incl.” in search queries indicates a demand for offline installation media, but it also raises significant red flags regarding authenticity, security, and legality.
Key Takeaway: This build is a historical artifact—not a production-ready OS. Downloading and installing it today is extremely risky outside of isolated, air-gapped virtual machines for research purposes.
| Threat Vector | Description |
|---------------|-------------|
| Pre-ransomware vulnerability | Unpatched SMB, RDP, and printer spooler exploits |
| Timebomb activation | System becomes unusable or resets every few hours |
| Telemetry from Microsoft | Insider builds still send diagnostic data |
| Trojanized ISOs | Attackers embed backdoors (e.g., modified install.wim with hidden admin account) |
| Expired certificates | Drivers and apps may fail to install or run |
| No Windows Update | Cannot get any security fixes, even for Defender definitions (unless manually updated via offline .cab) |
A user downloads “Win10_21390_x64.iso” from a torrent site. The ISO contains a hidden scheduled task that executes a coin miner after 72 hours. Since Defender is out of date, the miner remains undetected.