brew doctor falsely reports CLT 26.6 outdated in Intel macOS 26 because it uses arm64-only CLT 27 clang threshold

[gugu-hw]

brew doctor output

Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry or file an issue; just ignore this. Thanks!

Warning: Some installed casks are deprecated or disabled.
You should find replacements for the following casks:

  rar

Warning: A newer Command Line Tools release is available.
Update them from Software Update in System Settings.

If that doesn't show you any updates, run:
  sudo rm -rf /Library/Developer/CommandLineTools
  sudo xcode-select --install

Alternatively, manually download them from:
  https://developer.apple.com/download/all/.
You should download the Command Line Tools for Xcode 26.6.

Warning: You are using macOS on Intel x86_64.
We do not provide support for this platform (as-of September 2026, announced August 2025).

Apple have dropped Intel x86_64 support in macOS Golden Gate (27).
GitHub Actions are dropping macOS Intel x86_64 runners in 2027.
Homebrew is a non-profit project run entirely by volunteers, not employees.
If the biggest companies in the world cannot support macOS Intel x86_64
any longer, sadly neither can we.

Homebrew no longer builds bottles for this configuration.
Existing bottles may still work, but updated formulae may build from source.This is a Tier 3 configuration:
  https://docs.brew.sh/Support-Tiers#tier-3
You can report issues with Tier 3 configurations to Homebrew/* repositories!
  
Read the above document before opening any issues or PRs.

Verification

• I ran brew update twice and am still able to reproduce my issue.
• I have supplied my brew doctor output above and it seems unrelated to my issue.
• This issue's title and/or description do not reference a single formula e.g. brew install wget. If they do, open an issue at https://github.com/Homebrew/homebrew-core/issues/new/choose instead.
• I did not use AI/LLM to create this issue, or I disclosed the tool and model used; I will answer maintainer questions myself without AI/LLM.

brew config output

HOMEBREW_VERSION: 7.0.4
ORIGIN: https://github.com/Homebrew/brew
HEAD: edb70f031e4170c780799633a1226ff73e1077f4
Last commit: 3 days ago
Branch: stable
Core tap: N/A
Core cask tap: N/A
HOMEBREW_PREFIX: /usr/local
Homebrew Ruby: 4.0.7 => /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/4.0.7/bin/ruby
CPU: 20-core 64-bit cometlake
Clang: 21.0.0 build 2100
Git: 2.50.1 => /Applications/Xcode.app/Contents/Developer/usr/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.7-x86_64
CLT: 26.6.0.0.1781586589
Xcode: 26.6

What were you trying to do (and why)?

Normally updating Homebrew and upgrading my installed apps, it's a very normal demand.
I used ChatGPT to diagnose the issue and find that the problem is in Library/Homebrew/os/mac/xcode.rb, it uses the clang threshold for CLT 27 (2100.3.34.2) for both macOS 26 and 27.
324 # Bump these when the new version is distributed through Software Update
325 # and our CI systems have been updated.
326 sig { returns(String) }
327 def self.latest_clang_version
328 case MacOS.version
329 when "27", "26" then "2100.3.34.2"
330 when "15" then "1700.6.4.2"
331 when "14" then "1600.0.26.6"
332 when "13" then "1500.1.0.2.5"
333 when "12" then "1400.0.29.202"
334 else "1300.0.29.30"
335 end
336 end
Although macOS 26 on Apple Silicon can install Xcode 27 and its CLT, but Xcode 27 is arm-only so Intel macOS 26 is stopped at Xcode 26.6 and CLT 26.6, which has clang 2100.1.1.101.
$ clang -v
Apple clang version 21.0.0 (clang-2100.1.1.101)
Target: x86_64-apple-darwin25.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
The fix should be easy, separate the detection logic for 26 and 27, and for 26, add a x86 detection to use the version of CLT 26.6. However, I'm not that interested in forking and committing a pull request, so I will just create an issue.
The diagnosis is completed by LLM, but this issue creation is completed by me and written by hand.

What happened (include all command output)?

Homebrew will output the CLT outdated warning when building every new formulae from source, which is the same if I run brew doctor manually.
Warning: A newer Command Line Tools release is available.
Update them from Software Update in System Settings.

If that doesn't show you any updates, run:
sudo rm -rf /Library/Developer/CommandLineTools
sudo xcode-select --install

Alternatively, manually download them from:
https://developer.apple.com/download/all/.
You should download the Command Line Tools for Xcode 26.6.

What did you expect to happen?

No such warning shown

Step-by-step reproduction instructions (running brew commands)

brew update
brew install *
or brew upgrade *
* means any formula that has no bottle for Intel macOS in its latest version