I just came across these in the elasticsearch CI as well.  I’ve opened 
https://github.com/apache/lucene/pull/15563 to backport some of Robert’s 
changes.

> On 12 Jan 2026, at 14:24, Robert Muir <[email protected]> wrote:
> 
> On Mon, Jan 12, 2026 at 5:38 AM Dawid Weiss <[email protected]> wrote:
>> 
>> 
>> There is significant variance between runs on github - I think this view 
>> shows it clearly:
>> 
>> https://github.com/apache/lucene/actions/workflows/run-checks-all.yml?query=branch%3Amain
>> https://github.com/apache/lucene/actions/workflows/run-checks-all.yml?query=branch%3Abranch_10x
>> 
>> The slowness on 10x may be attributed to some cleanups to tests that have 
>> been only applied to main. This is my guess, at least. It would be worth 
>> reviewing and
>> reapplying those to 10x as well.
>> 
> 
> There were some particular tests that were extremely slow on windows and 
> macos.
> 
> But also there were some fairly invasive improvements on build side
> related to this problem:
> * we switched to more efficient runners on pr/push (ubuntu24.04-arm)
> and only triggering the macos at night.
> * use default flags (C2 compiler disabled, number of cores detection),
> this had a very large impact.
> 
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