[SOLVED] Fixing Homebrew Errors After macOS 26 Tahoe Update

If you’re encountering errors with the brew process after upgrading to macOS Tahoe 26 Preview—particularly one that looks like this:

/opt/homebrew/Library/Homebrew/macos_version.rb:53:in 'MacOSVersion#initialize': unknown or unsupported macOS version: "26.0" (MacOSVersion::Error)
	from /opt/homebrew/Library/Homebrew/os/mac.rb:44:in 'Class#new'
	from /opt/homebrew/Library/Homebrew/os/mac.rb:44:in 'OS::Mac.full_version'
	from /opt/homebrew/Library/Homebrew/os/mac.rb:32:in 'OS::Mac.version'
	from /opt/homebrew/Library/Homebrew/os.rb:60:in '<module:OS>'
	from /opt/homebrew/Library/Homebrew/os.rb:7:in '<main>'
	from <internal:/opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.4.4/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:37:in 'Kernel#require'
	from <internal:/opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.4.4/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:37:in 'Kernel#require'
	from /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.4.4/lib/ruby/gems/3.4.0/gems/bootsnap-1.18.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in 'Kernel#require'
	from /opt/homebrew/Library/Homebrew/global.rb:138:in '<top (required)>'
	from /opt/homebrew/Library/Homebrew/brew.rb:18:in 'Kernel#require_relative'
	from /opt/homebrew/Library/Homebrew/brew.rb:18:in '<main>'

You’re not alone. This issue arises because your Homebrew version doesn’t yet recognize macOS 26.0 as a valid or supported version. Let’s break down what’s happening, why it matters, and how to fix it.

What’s Actually Happening?

Homebrew maintains an internal list of supported macOS versions within its source code. When a major new version of macOS drops —even in preview— Homebrew doesn’t automatically know what to do with it.

In this case, the error occurs because:

• The Homebrew script is trying to parse the system version number, finds “26.0,” and says: “I’ve never heard of this one.”
• This triggers a MacOSVersion::Error, which effectively halts any brew command from running.

This isn’t a bug in your system—it’s just a gap in recognition.

Quick Fix: Update Homebrew

The Homebrew team usually responds quickly to new macOS versions—especially popular previews. To resolve this issue, simply run:

brew update

This pulls in the latest definitions, including support for macOS 26, allowing brew to identify your OS properly and continue working as expected.

Alternative Workaround (If brew update Fails)

If brew update itself is broken due to the version error (and sometimes it is), you can try running the update manually from within the Git repository:

cd /opt/homebrew
git fetch
git reset --hard origin/master

⚠️ Use this only if you know what you’re doing, as it can overwrite local changes in your Homebrew installation.

Why It Matters

Tools like Homebrew form the backbone of many development workflows. When they break after a system upgrade, even temporarily, it can cause ripple effects across your toolchain.

So while it’s tempting to jump onto the latest macOS preview, keep in mind:

• Many developer tools lag behind in support for preview releases.
• Some updates—especially to low-level tools like compilers or SDK managers—can cause more subtle issues later on.

Recommendation for Devs

1. If you rely heavily on brew for work or projects, consider waiting until Homebrew officially supports your OS version.
2. If you’re experimenting with macOS Tahoe 26 Preview on a secondary machine or partition, go ahead—but know that some tooling may require manual fixes like this one.