Proposal for macOS Intel Support deprecation timeline in ITK 6 (Retained in ITK 5)

[thewtex]

Proposal

Deprecate macOS Intel (x86_64) support in ITK 6, while maintaining it in ITK 5 as a long-term support (LTS) release. This aligns with Apple’s phased sunsetting of Intel Macs and industry-wide shifts toward Apple Silicon optimization.

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Rationale

1. Apple’s Official Transition Timeline

• Apple completed its transition to Apple Silicon in June 2023 with the Intel Mac Pro’s discontinuation¹.
• macOS 17 (2026) is projected to be Apple Silicon–only, ending major OS updates for Intel Macs²³.
• Security updates for Intel Macs will continue until ~2027 for newer models (e.g., 2019 iMac, Mac Pro) but lack feature parity²⁴.

2. Third-Party Software Trends

• Major developers (e.g., Adobe, Microsoft) now prioritize Apple Silicon optimizations, with some dropping Intel support entirely²⁴.
• ARM64 macOS now dominates developer toolchains, with Xcode and CI/CD pipelines increasingly excluding Intel⁴.

3. ITK Maintenance Burden

• Supporting legacy Intel macOS complicates builds, testing, and CI/CD for ARM64-specific optimizations.
• macOS Intel GitHub Action Runners (macos-13) are slower than the ARM counterparts.
• Deprecating Intel in ITK 6 allows focused resources on Apple Silicon performance.

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Proposed Implementation

• ITK 6:
  • Remove Intel macOS from build matrices.
  • Document deprecation in release notes, directing users to ITK 5 for legacy workflows.
• ITK 5:
  • Maintain Intel macOS support as an LTS branch until 2027 (aligned with Apple’s security update window).
  • Backport critical fixes only.

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Community Impact Considerations

• Affected Users: Researchers/clinicians relying on older Intel Macs for specialized hardware (e.g., GPUs, PCIe devices).
• Mitigation: Provide migration guides for Apple Silicon or Linux/Windows alternatives.
• Timeline: Target deprecation for ITK 6.0 (Q1 2026), coinciding with macOS 17’s expected release³.

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Supporting Data

Key Fact	Source
macOS 17 (2026) likely Apple Silicon–only	23
Final Intel Mac (Mac Pro) discontinued June 2023	1
Security updates until ~2027 for newer Intel Macs	24
Average 2-year security update window post-OS EOL	234

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Request for Feedback

Please share:

1. Use cases requiring Intel macOS support beyond 2026.
2. Concerns about legacy hardware/software dependencies.
3. Preferences for LTS backport policies in ITK 5.

References inline via linked sources. Data current as of April 2025.

Footnotes

1. https://en.wikipedia.org/wiki/Mac_transition_to_Apple_silicon ↩ ↩²

2. https://9to5mac.com/2024/06/19/got-an-intel-mac-future/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

3. https://9to5mac.com/apple-intel-mac-support/ ↩ ↩² ↩³ ↩⁴

4. https://computercity.com/desktops/mac/how-long-will-intel-macs-be-supported ↩ ↩² ↩³ ↩⁴ ↩⁵

[thewtex]

xref Discourse thread:

https://discourse.itk.org/t/proposal-to-deprecate-macos-intel-support-in-itk-6-retain-in-itk-5/7510

[seanm]

Big huge thumbs down from me.

Apple is infamous for dropping support for things quickly, it's not something we should aspire to follow IMNSHO.

ITK does not have much Apple-specific code, it's mostly cross-platform C++. I don't imagine there being many issues specific to the combination of macOS + Intel, especially since (presumably) macOS will be supported in general, and Intel will be supported in general.

Our customers tend to use their hardware for many many years. Our current oldest supported macOS is 10.13, and ITK master is working fine there today.

As a counter-proposal, I think it makes more sense to have a discussion about what minimum version of macOS ITK should support. The CPU architecture doesn't much matter with ITK being in C++, that's nicely abstracted by the compiler. For example, we've had discussions in the recent past about using std::filesystem; that would require upping our minimum macOS from 10.13 to 10.15, which I could get behind at this point. i.e. dropping old OSes to support new C++ is a more compelling argument that dropping a whole CPU architecture because 'others are doing it'.

As for CI, I already have macOS Intel bots submitting builds and tests, and can continue to do so. If GitHub drops macOS Intel, then finding issues only after merge the day after is not so bad.

[blowekamp]

I agree with @seanm it does seem a bit premature to drop intel support. However, if we are not able to build and run intel CI on GHA or Azure, then we can't really support them.

So, can the GHA arm Macs build and run intel ITK with rosetta with the allotted resources? If yes, we are capable of continued support if, no our support is subject to GHA/AZP still running intel systems.

[dzenanz]

I was surprised with the proposal to drop Intel Mac support, mostly because to keep supporting it does not really require any action in the near future. I don't have use cases for Intel Macs, so I don't care much about it. But having a wider platform support is generally better. So we should probably postpone this consideration for the time when there is some identifiable effort required to keep supporting Intel Macs.

[N-Dekker]

Thanks for the elaborate proposal, Matt!

The good news: it appears that on GitHub Actions macos-14 is already amd64, as I understand from https://github.com/actions/runner-images/blob/0e37973a015a27a4a410a4ae37c0aa99bdd63ea8/README.md#available-images

However, on Azure Pipelines, macOS-14 is still Intel. Right? Looking at https://learn.microsoft.com/en-us/azure/devops/pipelines/agents/hosted?view=azure-devops&tabs=yaml#software which says:

macOS 14 Sonoma macOS-14 macOS-latest OR macOS-14 Link

Which links to macos-14-Readme.md, not to macos-14-arm64-Readme.md! 🤷

Related issues:

• Add macOS-14 (arm64) & macOS-15 (arm64) & macOS-26 (arm64) Image to Azure Pipelines actions/runner-images#8971
• Add macOS arm64 images (Apple Silicon) to Azure Pipelines actions/runner-images#11834

[dzenanz]

I remember that there was some MacOS image generation that had "Large" variant with a different ISA (AMD64/ARM64) from regular variant. Maybe MacOS-14?

[cookpa]

I remember that there was some MacOS image generation that had "Large" variant with a different ISA (AMD64/ARM64) from regular variant. Maybe MacOS-14?

I think that's right, for Github Team / Enterprise subscribers. There are 'large' Intel-based runners for Mac OS 14 and 15. Free tier users only have the standard macos-13 runner.

[seanm]

However, if we are not able to build and run intel CI on GHA or Azure, then we can't really support them.

Thinking about it, that's a sad state of affairs when an open source project like ITK is so captured by the Microsoft juggernaut that, even when we have cdash and community CI submissions like mine, such a statement could be made. :(

[SimonRit]

I was surprised with the proposal to drop Intel Mac support, mostly because to keep supporting it does not really require any action in the near future. I don't have use cases for Intel Macs, so I don't care much about it. But having a wider platform support is generally better. So we should probably postpone this consideration for the time when there is some identifiable effort required to keep supporting Intel Macs.

There are still Intel mac users around me and I would also prefer to keep its support. However, we have already dropped support for remote modules due to maintenance issues in InsightSoftwareConsortium/ITKRemoteModuleBuildTestPackageAction#109. It would be great if those were also maintained... but having spent some time maintaining the remote module infrastructure, I understand the choice.

[jamesobutler]

@seanm Do you use any of the itk python remote modules to have noticed there hasn’t been macOS x86_64 whls available? I haven’t seen any GitHub user reports about the drop of support for the following:

itk-elastix with ~11000 monthly downloads
itk-ants with ~2200 monthly downloads

I have pretty much dropped macOS x86_64 support because starting with PyTorch 2.3.0 (released April 24th 2024) there are no more macOS x86_64 whls.