Document breaking change: dotnet CLI commands log non-command-relevant data to stderr (#48924)

Author: Copilot

docs/core/compatibility/10.0.md

@@ -105,6 +105,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 | Title | Type of change    | Introduced version |
 |-------|-------------------|--------------------|
 | [.NET CLI `--interactive` defaults to `true` in user scenarios](sdk/10.0/dotnet-cli-interactive.md) | Behavioral change | Preview 3 |
+| [`dotnet` CLI commands log non-command-relevant data to stderr](sdk/10.0/dotnet-cli-stderr-output.md) | Behavioral change | RC 2 |
 | [.NET tool packaging creates RuntimeIdentifier-specific tool packages](sdk/10.0/dotnet-tool-pack-publish.md) | Behavioral change | Preview 6 |
 | [Default workload configuration from 'loose manifests' to 'workload sets' mode](sdk/10.0/default-workload-config.md) | Behavioral change | Preview 2 |
 | [`dotnet new sln` defaults to SLNX file format](sdk/10.0/dotnet-new-sln-slnx-default.md) | Behavioral change | RC 1 |

docs/core/compatibility/sdk/10.0/dotnet-cli-stderr-output.md

@@ -0,0 +1,41 @@
+---
+title: "Breaking change - dotnet CLI commands log non-command-relevant data to stderr"
+description: "Learn about the breaking change in .NET 10 where some dotnet CLI commands log verbose and non-command-relevant data to stderr instead of stdout."
+ms.date: 10/08/2025
+ai-usage: ai-generated
+ms.custom: https://dev.azure.com/msft-skilling/Content/_workitems/edit/494515
+---
+
+# dotnet CLI commands log non-command-relevant data to stderr
+
+Starting in .NET 10, some `dotnet` CLI command output that isn't core to the command being invoked emits to `stderr` instead of `stdout`.
+
+## Version introduced
+
+.NET 10 RC 2
+
+## Previous behavior
+
+Previously, first-run messages for the `dotnet` CLI emitted to `stdout`.
+
+## New behavior
+
+Starting in .NET 10, first-run messages for the `dotnet` CLI emit to `stderr`. (In the future, more messages will undergo a similar change.)
+
+## Type of breaking change
+
+This change is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+Information that's written to `stdout` that isn't directly related to the command being invoked inhibits the use of commands in scripting or noninteractive circumstances. When non-primary outputs like diagnostics, verbose messages, and incidental notifications are moved to `stderr`, `stdout` remains clean for parsing or other interpretation.
+
+## Recommended action
+
+For most non-PowerShell users, this change shouldn't require any action.
+
+For PowerShell users, we recommend using at least PowerShell version 7.2, where redirecting to `stderr` doesn't set PowerShell's `$Error` variable and cause PowerShell to think the previous command failed execution.
+
+## Affected APIs
+
+None.

docs/core/compatibility/toc.yml

@@ -114,6 +114,8 @@ items:
             items:
               - name: .NET CLI `--interactive` defaults to `true` in user scenarios
                 href: sdk/10.0/dotnet-cli-interactive.md
+              - name: "`dotnet` CLI commands log non-command-relevant data to stderr"
+                href: sdk/10.0/dotnet-cli-stderr-output.md
               - name: .NET tool packaging creates RuntimeIdentifier-specific tool packages
                 href: sdk/10.0/dotnet-tool-pack-publish.md
               - name: "`dotnet restore` audits transitive packages"

docs/core/tools/telemetry.md

@@ -33,7 +33,10 @@ A single telemetry entry is also sent by the .NET SDK installer when a successfu
 
 ## Disclosure
 
-The .NET SDK displays text similar to the following when you first run one of the [.NET CLI commands](index.md) (for example, `dotnet build`). Text may vary slightly depending on the version of the SDK you're running. This "first run" experience is how Microsoft notifies you about data collection.
+The .NET SDK displays text similar to the following when you first run one of the [.NET CLI commands](index.md) (for example, `dotnet build`). Text might vary slightly depending on the version of the SDK you're running. This "first run" experience is how Microsoft notifies you about data collection.
+
+> [!NOTE]
+> **Breaking change:** The behavior of telemetry messages written to `stderr` has changed in recent versions of the .NET SDK. For more information, see the [breaking change documentation](/dotnet/core/compatibility/sdk/8.0/telemetry-stderr-behavior).
 
 ```console
 Telemetry