diff --git a/main/src/main/scala/sbt/ProjectMatrix.scala b/main/src/main/scala/sbt/ProjectMatrix.scala
index cca1bbafa..1b834ded7 100644
--- a/main/src/main/scala/sbt/ProjectMatrix.scala
+++ b/main/src/main/scala/sbt/ProjectMatrix.scala
@@ -701,7 +701,7 @@ object ProjectMatrix {
 
   // called by macro
   def apply(id: String, base: File): ProjectMatrix = {
-    val defaultDefAxes = Seq(VirtualAxis.jvm, VirtualAxis.scalaABIVersion("2.13.3"))
+    val defaultDefAxes = Seq(VirtualAxis.jvm, VirtualAxis.scalaABIVersion("3.3.3"))
     val matrix = unresolved(
       id,
       base,
diff --git a/sbt-app/src/sbt-test/project-matrix/jvm-sandwich/test b/sbt-app/src/sbt-test/project-matrix/jvm-sandwich/test
index 18ed59f1b..211f8023c 100644
--- a/sbt-app/src/sbt-test/project-matrix/jvm-sandwich/test
+++ b/sbt-app/src/sbt-test/project-matrix/jvm-sandwich/test
@@ -2,6 +2,6 @@
 
 > fooApp3_0_0_M1/compile
 
-> barApp/compile
+> barApp2_13/compile
 
-> bazApp/check
+> bazApp2_13/check
diff --git a/sbt-app/src/sbt-test/project-matrix/jvm-with-scoping/test b/sbt-app/src/sbt-test/project-matrix/jvm-with-scoping/test
index 9c17bbfa5..4e56ffd41 100644
--- a/sbt-app/src/sbt-test/project-matrix/jvm-with-scoping/test
+++ b/sbt-app/src/sbt-test/project-matrix/jvm-with-scoping/test
@@ -3,4 +3,4 @@
 $ exists target/out/jvm/scala-2.13.3/core/backend/a/Core.class
 $ exists target/out/jvm/scala-2.12.12/core/backend/a/Core.class
 
-> core/check
+> core2_13/check
diff --git a/sbt-app/src/sbt-test/project-matrix/jvm/build.sbt b/sbt-app/src/sbt-test/project-matrix/jvm/build.sbt
index 65b08b9e6..4ca6ea63e 100644
--- a/sbt-app/src/sbt-test/project-matrix/jvm/build.sbt
+++ b/sbt-app/src/sbt-test/project-matrix/jvm/build.sbt
@@ -1,5 +1,5 @@
 lazy val scala213 = "2.13.3"
-lazy val scala212 = "2.12.12"
+lazy val scala3 = "3.4.2"
 lazy val check = taskKey[Unit]("")
 
 lazy val root = (project in file("."))
@@ -13,7 +13,7 @@ lazy val app = (projectMatrix in file("app"))
   .settings(
     name := "app"
   )
-  .jvmPlatform(scalaVersions = Seq(scala213))
+  .jvmPlatform(scalaVersions = Seq(scala3))
 
 lazy val core = (projectMatrix in file("core"))
   .settings(
@@ -22,7 +22,7 @@ lazy val core = (projectMatrix in file("core"))
       assert(projectMatrixBaseDirectory.value == file("core"))
     },
   )
-  .jvmPlatform(scalaVersions = Seq(scala213, scala212))
+  .jvmPlatform(scalaVersions = Seq(scala213, scala3))
 
 lazy val intf = (projectMatrix in file("intf"))
   .settings(
diff --git a/sbt-app/src/sbt-test/project-matrix/jvm/test b/sbt-app/src/sbt-test/project-matrix/jvm/test
index 9c17bbfa5..40966a833 100644
--- a/sbt-app/src/sbt-test/project-matrix/jvm/test
+++ b/sbt-app/src/sbt-test/project-matrix/jvm/test
@@ -1,6 +1,6 @@
 > compile
 
 $ exists target/out/jvm/scala-2.13.3/core/backend/a/Core.class
-$ exists target/out/jvm/scala-2.12.12/core/backend/a/Core.class
+$ exists target/out/jvm/scala-3.4.2/core/backend/a/Core.class
 
 > core/check
diff --git a/sbt-app/src/sbt-test/project-matrix/lib/build.sbt b/sbt-app/src/sbt-test/project-matrix/lib/build.sbt
index 8a4cb65a2..00ace3bdf 100644
--- a/sbt-app/src/sbt-test/project-matrix/lib/build.sbt
+++ b/sbt-app/src/sbt-test/project-matrix/lib/build.sbt
@@ -1,4 +1,4 @@
-ThisBuild / version := "0.1.0-SNAPSHOT"
+version := "0.1.0-SNAPSHOT"
 
 lazy val util = projectMatrix
   .jvmPlatform(scalaVersions = Seq("2.12.19", "2.13.13"))
diff --git a/sbt-app/src/sbt-test/project-matrix/lib/test b/sbt-app/src/sbt-test/project-matrix/lib/test
index 5379ef8b1..5fd81a7d0 100644
--- a/sbt-app/src/sbt-test/project-matrix/lib/test
+++ b/sbt-app/src/sbt-test/project-matrix/lib/test
@@ -12,4 +12,4 @@ $ copy-file target/out/jvm/scala-2.12.19/strayjar/strayjar_2.12-0.1.0-SNAPSHOT.j
 # check ss
 $ mkdir ss/lib
 $ copy-file target/out/jvm/scala-2.12.19/strayjar/strayjar_2.12-0.1.0-SNAPSHOT.jar ss/lib/strayJar.jar
-> ss/compile
+> ss2_13/compile