brew update generates Error: private method 'fetch' called for class CoreCaskTap

[xyzzy314]

brew doctor output

Your system is ready to brew.

Verification

• I ran brew update twice and am still able to reproduce my issue.
• My "brew doctor output" above says Your system is ready to brew or a definitely unrelated Tier message.
• 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.

brew config output

HOMEBREW_VERSION: 6.0.3-44-g988a7ca
ORIGIN: https://github.com/Homebrew/brew
HEAD: 988a7ca1d80a6cc8e8449b0f91e898f1399ceea9
Last commit: 8 hours ago
Branch: main
Core tap HEAD: 92a7e0981d4608f81cccef4fa3fa4af485b5fd7f
Core tap last commit: 20 minutes ago
Core cask tap origin: https://github.com/caskroom/homebrew-cask
Core cask tap HEAD: 14e7175d9af61bb8e96175aa41a704102abc1b70
Core cask tap last commit: 64 minutes ago
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CASK_OPTS: []
HOMEBREW_DOWNLOAD_CONCURRENCY: 64
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_MAKE_JOBS: 32
HOMEBREW_REQUIRE_TAP_TRUST: set
Homebrew Ruby: 4.0.5 => /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/4.0.5_1/bin/ruby
CPU: 32-core 64-bit skylake
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: 26.5.1-x86_64
CLT: 26.5.0.0.1777544298
Xcode: 26.5

What were you trying to do (and why)?

Update brew. Because it's good to do regularly.

What happened (include all command output)?

[~] -> brew update -v
Checking if we need to fetch /usr/local/Homebrew...
==> Updating Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/1password/homebrew-tap...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Checking if we need to fetch internal/packages.tahoe.jws.json...
Error: private method 'fetch' called for class CoreCaskTap
/usr/local/Homebrew/Library/Homebrew/tap.rb:556:in 'Tap#apply_redirected_remote!'
/usr/local/Homebrew/Library/Homebrew/cmd/update-report.rb:79:in 'block in Homebrew::Cmd::UpdateReport#output_update_report'
/usr/local/Homebrew/Library/Homebrew/cmd/update-report.rb:73:in 'Pathname#each_line'
/usr/local/Homebrew/Library/Homebrew/cmd/update-report.rb:73:in 'Homebrew::Cmd::UpdateReport#output_update_report'
/usr/local/Homebrew/Library/Homebrew/cmd/update-report.rb:34:in 'Homebrew::Cmd::UpdateReport#run'
/usr/local/Homebrew/Library/Homebrew/brew.rb:121:in '

'
Please report this issue:

What did you expect to happen?

For brew to get a list of things to update. Interestingly, "brew upgrade" seems to be working.

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

Start shell.
Run brew update (or brew update -v)
Error occurs.

New behaviour; didn't do it a few weeks ago, but started doing it recently.