diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index f6a06007b..7c91be7eb 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -3624,7 +3624,13 @@ object Classpaths {
         o %% "librarymanagement-ivy",
         o %% "util-logging",
         o %% "util-position",
-        o %% "io"
+        o %% "io",
+        "com.eed3si9n" %% "sjson-new-core",
+        "com.eed3si9n" %% "gigahorse-core",
+        "com.typesafe" %% "ssl-config-core",
+        "org.reactivestreams" % "reactive-streams",
+        "org.slf4j" % "slf4j-api",
+        "com.typesafe" % "config",
       )
       if (isMeta && !force) excludes.toVector ++ sbtModulesExcludes
       else excludes
diff --git a/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/build.sbt b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/build.sbt
new file mode 100644
index 000000000..e2734d0de
--- /dev/null
+++ b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/build.sbt
@@ -0,0 +1,69 @@
+ThisBuild / scalaVersion := "3.8.4"
+ThisBuild / organization := "com.example"
+
+libraryDependencies += "com.typesafe" % "config" % "1.4.5"
+
+val checkMetabuildClasspath = taskKey[Unit]("Checks the effective metabuild classpath")
+val checkProjectClasspath = taskKey[Unit]("Checks the project classpath")
+
+checkMetabuildClasspath := Def.uncached {
+  val buildUnit = loadedBuild.value.units(thisProjectRef.value.build).unit
+  val classpath = buildUnit.plugins.pluginData.dependencyClasspath
+  val managedModules = classpath
+    .flatMap(_.get(Keys.moduleIDStr))
+    .map(Classpaths.moduleIdJsonKeyFormat.read)
+    .map(module => module.organization -> module.name)
+    .toSet
+  val launcherOwnedModules = Set(
+    "com.eed3si9n" -> "sjson-new-core_3",
+    "com.eed3si9n" -> "gigahorse-core_3",
+    "com.typesafe" -> "ssl-config-core_3",
+    "org.reactivestreams" -> "reactive-streams",
+    "org.slf4j" -> "slf4j-api",
+    "com.typesafe" -> "config",
+  )
+  val pluginModules = Set(
+    "ch.epfl.scala" -> "sbt-github-dependency-submission_sbt2_3",
+    "com.eed3si9n" -> "gigahorse-asynchttpclient_3",
+    "com.eed3si9n" -> "shaded-asynchttpclient",
+  )
+  val converter = buildUnit.converter
+  val launcherJars = classpath
+    .filter(_.get(Keys.moduleIDStr).isEmpty)
+    .map(entry => converter.toPath(entry.data).getFileName.toString)
+  val launcherJarNames = Set(
+    "sjson-new-core_3",
+    "gigahorse-core_3",
+    "ssl-config-core_3",
+    "reactive-streams",
+    "slf4j-api",
+    "config",
+  )
+
+  assert(
+    managedModules.intersect(launcherOwnedModules).isEmpty,
+    s"found plugin-managed sbt modules: ${managedModules.intersect(launcherOwnedModules)}",
+  )
+  assert(
+    pluginModules.subsetOf(managedModules),
+    s"missing plugin modules: ${pluginModules.diff(managedModules)}",
+  )
+  assert(
+    launcherJarNames.forall(name => launcherJars.count(_.startsWith(s"$name-")) == 1),
+    s"expected one launcher jar for each sbt module: $launcherJars",
+  )
+}
+
+checkProjectClasspath := Def.uncached {
+  val modules = (Compile / externalDependencyClasspath).value
+    .flatMap(_.get(Keys.moduleIDStr))
+    .map(Classpaths.moduleIdJsonKeyFormat.read)
+  assert(
+    modules.exists(module =>
+      module.organization == "com.typesafe" &&
+        module.name == "config" &&
+        module.revision == "1.4.5"
+    ),
+    s"missing project dependency: $modules",
+  )
+}
diff --git a/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/project/Example.scala b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/project/Example.scala
new file mode 100644
index 000000000..6adfcfc9f
--- /dev/null
+++ b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/project/Example.scala
@@ -0,0 +1,6 @@
+import sbt.*
+import sbt.Keys.*
+
+object Example {
+  lazy val settings = Seq(javaOptions += "-Dfoo=bar")
+}
diff --git a/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/project/plugins.sbt b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/project/plugins.sbt
new file mode 100644
index 000000000..3ae2b253a
--- /dev/null
+++ b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/project/plugins.sbt
@@ -0,0 +1 @@
+addSbtPlugin("ch.epfl.scala" % "sbt-github-dependency-submission" % "3.2.3")
diff --git a/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/test b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/test
new file mode 100644
index 000000000..0fcd00471
--- /dev/null
+++ b/sbt-app/src/sbt-test/project/i8207-sjson-new-downgrade/test
@@ -0,0 +1,10 @@
+# Issue 8207: a metabuild plugin must not downgrade sjson-new core.
+# Loading this build exercises the metabuild compile, which summons
+# the JsonFormat for String via the caching macro on javaOptions.
+# When the plugin downgrades sjson-new core on the metabuild
+# classpath, project load fails with a missing given. A successful
+# load is the regression assertion.
+> projects
+> checkMetabuildClasspath
+> checkProjectClasspath
+> githubGenerateSnapshot {}