Microsoft Support documents KB5123777 as Qualcomm QNN Execution Provider version 2.2608.0.0 for Windows 11 24H2 and 25H2, replacing KB5121775. A companion support bulletin identifies KB5124879 as Phi Silica version 1.2608.951.0 for Qualcomm-powered Copilot+ PCs, replacing KB5121639. Both install automatically through Windows Update once the current cumulative update is present.
The August 25 KB5122385 package belongs to a much older Windows servicing model: it is a cumulative .NET Framework 3.5 and 4.8.1 update for Windows 11 25H2 and Microsoft server operating system 24H2. Microsoft says it adds no new security fixes, addresses intermittent crashes in some 64-bit .NET Framework scenarios, and has no known issues at publication. Its appearance next to a language model and silicon-specific inference software is the point. One Windows update queue now carries code from the traditional enterprise runtime through to a model running locally on an NPU.
KB5123777 updates the route from an app to Qualcomm hardware
Calling KB5123777 an “NPU driver” misses the mechanism. Microsoft describes QNN as an execution provider for ONNX Runtime and Windows machine-learning scenarios. The provider uses Qualcomm’s AI Engine Direct SDK to turn an ONNX model into a QNN graph, then runs that graph through a supported accelerator backend.
In plain terms, an app can supply a compatible model to Windows ML; Windows ML and ONNX Runtime provide the common inference layer; the QNN provider supplies the Qualcomm-specific implementation that decides how supported operations reach the underlying accelerator. The QNN path can use Qualcomm hardware including the Hexagon NPU where the model, driver, provider, and device support line up. It is a shared infrastructure component, rather than a feature embedded permanently inside every AI application.
Microsoft Learn’s Windows ML documentation confirms that vendor execution providers are separately available on Windows 11 24H2 build 26100 or newer, subject to device and driver compatibility. The company’s design lets applications obtain certified providers through the Windows ML catalog, while Windows Update services newer versions through optional non-security preview releases. That gives developers a smaller application footprint and means a compatible application can gain an updated accelerator implementation without shipping a new installer.
There is a less glamorous implication for managed environments. Microsoft’s own developer guidance says organizations needing strict version control, offline support, or devices where Windows Update is restricted may instead bundle the execution-provider binaries themselves. In exchange, the organization owns the compatibility testing among Windows ML, ONNX Runtime, and the provider version. The convenient shared platform and strict reproducibility are competing deployment choices, not outcomes an administrator gets simultaneously by default.
Microsoft says KB5123777 contains improvements, but it has not published a benchmark, model matrix, latency measurement, power result, or detailed change log. There is no factual basis to promise higher TOPS, a particular percentage speedup, better battery life, or broader model compatibility after this update. The verified news is the independently serviceable layer, not a quantifiable performance claim.
Phi Silica is a versioned Windows component, not a static inbox feature
KB5124879 updates Phi Silica to version 1.2608.951.0 on Qualcomm-powered Copilot+ PCs running Windows 11 24H2 or 25H2. Microsoft describes Phi Silica as its Transformer-based small language model optimized to run on-device through the NPU, exposing capabilities including text understanding, summarization, rewriting, and short-form generation through Windows AI APIs.
The support article deliberately says only that the package includes “improvements.” It does not say Phi Silica was retrained, became more accurate, altered its safety behavior, expanded its context window, or performs faster. Administrators should resist treating a component version number as a scorecard for model quality.
What it does establish is a servicing boundary. An app using the Windows AI APIs can remain unchanged while the local model below it changes. The operating system build may stay constant; the app binary may stay constant; the same prompt may produce a different answer because the underlying model component changed. That is familiar territory for browser engines, drivers, and language runtimes, but it is a different level of repeatability concern when the dependency generates text rather than merely rendering a page or parsing a file.
Microsoft’s current Phi Silica documentation makes the lifecycle more explicit. It says Phi Silica is scheduled to be replaced by Aion Instruct: a sideloadable test and LoRA-training package is planned for early October 2026; a Windows Insider rollout is planned during October, with Phi Silica still installed and a Controlled Feature Rollout selecting the active model; and retail rollout with Phi Silica removal is planned for November 2026. These are Microsoft’s plans as of August 28, not completed releases.
The transition is revealing. Microsoft is positioning the Windows AI API as the long-lived application contract and the local model as a replaceable implementation. Aion Instruct is also planned to remove Phi Silica’s Limited Access Feature token requirement. That may lower adoption friction for developers, but it makes version-aware testing more important. An organization validating a local summarization workflow in September could be running a different model in November without an application redeployment.
Copilot+ eligibility still limits what arrives
Neither AI package should be read as a universal ARM64 Windows update. Microsoft’s KB5124879 notice explicitly applies to Copilot+ PCs only, and its Phi Silica page describes the August package as being for Qualcomm-powered Copilot+ systems. The QNN provider also has a hardware and driver dependency: Microsoft’s current Windows ML documentation lists Snapdragon X Elite and Snapdragon X Plus systems with a Qualcomm Hexagon NPU driver at version 30.0.140.0 or higher.
That distinction matters when reading the August 27 optional Windows 11 preview, KB5120998. The preview applies to Windows 11 25H2 build 26200.9278 and 24H2 build 26100.9278 and includes broader user-facing changes such as taskbar placement options, revised Start-menu sizing and recommendation controls, search-source labeling, and File Explorer refinements. It also carries deeper platform work around Microsoft Execution Containers, agent-process identification, Administrator Protection, ML-KEM support for TLS key exchange, and WMIC removal.
But the AI component updates associated with that release are limited to qualifying Copilot+ hardware, and the preview’s user-facing features are subject to gradual rollout. Installing build 26200.9278 or 26100.9278 does not guarantee that every advertised experience appears immediately. Likewise, the roughly 4.8 GB ARM64 Microsoft Update Catalog package is the size of the standalone catalog package, not a reliable measure of what an individual PC downloads or proof that every byte corresponds to a visible feature.
Microsoft Execution Containers are worth particular caution because the name invites overclaiming. They are a lightweight, policy-controlled process-isolation mechanism that can restrict files, networking, UI, and other capabilities for workloads such as coding agents and model-generated code. They do not make arbitrary generated code safe. Agent-process identification similarly provides context propagation through process tokens and potentially Windows Account Manager authentication requests; it is identification, not containment or authorization. Administrator Protection remains off by default and is not a formal security boundary.
KB5122385 is the reminder to keep normal change control
KB5122385 is the least flashy component in this cycle, and for most IT departments it may be the most immediately relevant. Microsoft places it in the optional-update channel and says the package fixes intermittent crashes in some 64-bit .NET Framework scenarios. The company currently lists no known issues.
The absence of a known issue for KB5122385 should not be confused with a clean bill of health for every .NET workload. Microsoft documented a WPF font-subsetting problem affecting some printing and PDF or XPS-generation scenarios for the separate August 11 security update KB5120708. There is no evidence in the current KB5122385 record that attributes that issue to the August 25 update, so administrators should not carry the defect forward by assumption. They should, however, test the business processes that matter.
A sensible pilot ring for this update cycle includes WPF printing and PDF/XPS generation, line-of-business .NET applications, VPN and authentication clients, endpoint security tools, and any internally developed software calling Windows AI or Windows ML APIs. Windows Update for Business can offer KB5122385, while Microsoft says the optional KB5120998 Windows preview itself is not directly delivered through that channel; its changes arrive with the subsequent security update instead.
The practical inventory has changed. Alongside OS build, firmware, drivers, .NET level, and application version, organizations deploying local AI should record the Windows ML runtime, the execution-provider version, the installed model or AI-component version, hardware identity, and representative output behavior. For a deterministic workflow, preserving test prompts and expected acceptance criteria will matter more than a generic assertion that the feature still “works.”
Windows on ARM spent years proving that it could run the existing Windows software estate. The August 27 servicing stack shows Microsoft building a native local-AI platform around Qualcomm hardware as well. The management challenge is now part of the feature: when model and accelerator software update independently, IT needs clear inventories, predictable rollout controls, test guidance, and a documented recovery path before those components can be treated as routine Windows dependencies.