macos-26 host OS is still macOS 26.3, which blocks tests for projects targeting macOS 26.4

[cypherair]

Description

The current macos-26 hosted runner still reports macOS 26.3, which blocks macOS test execution for projects that require macOS 26.4.

In our case, the workflow runs on runs-on: macos-26, the project sets MACOSX_DEPLOYMENT_TARGET = 26.4, and xcodebuild test fails before tests begin because the host runner OS is still 26.3.

Minimal workflow snippet:

jobs:
  swift-unit-tests:
    runs-on: macos-26
    steps:
      - uses: actions/checkout@v4
      - name: Run CypherAir unit tests
        run: |
          xcodebuild test \
            -scheme CypherAir \
            -project CypherAir.xcodeproj \
            -testPlan CypherAir-UnitTests \
            -destination 'platform=macOS,arch=arm64'

For the same image version, the public Included Software README also reports:

• OS Version: macOS 26.3 (25D125)
• Image Version: 20260408.0337.1

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 22.04
• Ubuntu 24.04
• Ubuntu Slim
• macOS 14
• macOS 14 Arm64
• macOS 15
• macOS 15 Arm64
• macOS 26
• macOS 26 Arm64
• Windows Server 2022
• Windows Server 2025
• Windows Server 2025 with Visual Studio 2026

Image version and build link

Failed public workflow run:
https://github.com/cypherair/cypherair/actions/runs/24251859743/job/70813100853

Runner image from Set up job:

• Image: macos-26-arm64
• Version: 20260408.0337.1
• Included Software: https://github.com/actions/runner-images/blob/macos-26-arm64/20260408.0337/images/macos/macos-26-arm64-Readme.md
• Image Release: https://github.com/actions/runner-images/releases/tag/macos-26-arm64%2F20260408.0337

Is it regression?

No / not observed as a regression. We do not currently have a successful GitHub-hosted run on a macOS 26.4 host to use as a last known good.

Expected behavior

macos-26 should provide a host OS of macOS 26.4 or newer so that macOS targets/tests with a 26.4 deployment target can build and run on GitHub-hosted runners.

Actual behavior

The runner image includes the relevant Xcode/SDK content, but the host OS is still macOS 26.3. As a result, xcodebuild test -destination 'platform=macOS,arch=arm64' fails before tests start with:

xcodebuild: error: Failed to build project CypherAir with scheme CypherAir.: Cannot test target "CypherAirTests" on "My Mac": My Mac's macOS 26.3 doesn't match CypherAirTests's macOS 26.4 deployment target.

Repro steps

1. Configure a macOS target with MACOSX_DEPLOYMENT_TARGET = 26.4.
2. Run a GitHub Actions workflow on runs-on: macos-26.
3. Execute xcodebuild test -destination 'platform=macOS,arch=arm64'.
4. Observe that the job fails before tests begin because the runner host is still macOS 26.3.