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sbt 1.9.6

Hi everyone. On behalf of the sbt project, I’m happy to announce sbt 1.9.6 patch release is available. Full release note is here -

See 1.9.0 release note for the details on 1.9.x features.


How to upgrade

The sbt version used for your build must be upgraded by putting the following in project/


This mechanism allows that sbt 1.9.6 is used only for the builds that you want.

Download the official sbt runner from, cs setup, SDKMAN, or download from to upgrade the sbt shell script and the launcher.

Zinc regression

We’re still investigating on the details, but per Lukas on scala/bug#12868:

Say we have package p { class C { def m { new anon { def sol } } } }.

The phase travel exitingFlatten added in sbt/zinc#1244 causes the (cached) flatname of ClassSymbol for the anonymous class to be computed after the flatten phase. The owner chain of the symbol is different at this point. So instead of something like p.C$m$anon we end up with only p.m$anon.

The error in Pekko is due to two anonymous classes now having the same name accidentally. However, I believe that this has a broad effect, many anonymous classes will get a different name when compiling with the new zinc.

While it’s possibly OK in terms of binary compatibiliy (anonymous classes cannot be referenced externally), it’s still an unintended wide-reaching change.

It probably should be considered a bug in the compiler, but we cannot change existing compiler releases. The new Zinc needs to continue working with existing compiler releases.

I merged sbt/zinc#1244 with a cursory review (it looked ok to me), so I take responsibility on this regression. IT’S ME HI.


Thanks to everyone who’s helped improve sbt and Zinc by using them, reporting bugs, improving our documentation, porting builds, porting plugins, and submitting and reviewing pull requests.

For anyone interested in helping sbt, there are many avenues for you to help, depending on your interest. If you’re interested, Contributing, “help wanted”, “good first issue”, and Discussions are good starting points.

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