diff --git a/core/pom.xml b/core/pom.xml
index 720b509c2..91000d4d6 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -5,10 +5,13 @@
   <parent>
     <groupId>com.google.truth</groupId>
     <artifactId>truth-parent</artifactId>
-    <version>HEAD-SNAPSHOT</version>
+    <version>999.0.0-SNAPSHOT</version>
   </parent>
   <artifactId>truth</artifactId>
   <name>Truth Core</name>
+  <properties>
+    <test.add.exports></test.add.exports>
+  </properties>
   <dependencies>
     <dependency>
       <groupId>com.google.guava</groupId>
@@ -128,6 +131,9 @@
       </plugin>
       <plugin>
         <artifactId>maven-surefire-plugin</artifactId>
+        <configuration>
+          <argLine>${test.add.exports}</argLine>
+        </configuration>
         <executions>
           <execution>
             <id>default-test</id>
@@ -263,6 +269,42 @@
     </plugins>
   </reporting>
   <profiles>
+    <profile>
+      <id>java9-plus</id>
+      <activation>
+        <jdk>[9,)</jdk>
+      </activation>
+      <properties>
+        <!--
+          For tests of the sample Employee extension, which would otherwise fail:
+          java.lang.reflect.InaccessibleObjectException: Unable to make public void com.google.common.truth.extension.EmployeeSubjectTest.username() accessible: module com.google.truth does not "exports com.google.common.truth.extension" to module junit
+        -->
+        <test.add.exports>--add-exports com.google.truth/com.google.common.truth.extension=junit,ALL-UNNAMED</test.add.exports>
+      </properties>
+      <build>
+        <plugins>
+          <plugin>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <executions>
+              <execution>
+                <id>compile-java9</id>
+                <phase>compile</phase>
+                <goals>
+                  <goal>compile</goal>
+                </goals>
+                <configuration>
+                  <release>9</release>
+                  <compileSourceRoots>
+                    <compileSourceRoot>${project.basedir}/src/main/java9</compileSourceRoot>
+                  </compileSourceRoots>
+                  <multiReleaseOutput>false</multiReleaseOutput>
+                </configuration>
+              </execution>
+            </executions>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
     <profile>
       <id>java8</id>
       <activation>
diff --git a/core/src/main/java9/module-info.java b/core/src/main/java9/module-info.java
new file mode 100644
index 000000000..a78387ad7
--- /dev/null
+++ b/core/src/main/java9/module-info.java
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2025 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module com.google.truth {
+  requires transitive com.google.common;
+
+  /*
+   * AutoValue's annotations aren't ready for the module system:
+   * https://github.com/google/auto/issues/597. Let's hope that our usages are internal enough that
+   * we don't need to worry about listing them here.
+   */
+
+  requires static transitive com.google.errorprone.annotations;
+  requires static transitive com.google.j2objc.annotations;
+  requires static transitive junit;
+  requires static transitive org.jspecify;
+  requires static transitive org.objectweb.asm;
+
+  exports com.google.common.truth;
+}
diff --git a/core/src/test/java/com/google/common/truth/CorrespondenceExceptionStoreTest.java b/core/src/test/java/com/google/common/truth/CorrespondenceExceptionStoreTest.java
index 6b18bacb7..feb25fbaa 100644
--- a/core/src/test/java/com/google/common/truth/CorrespondenceExceptionStoreTest.java
+++ b/core/src/test/java/com/google/common/truth/CorrespondenceExceptionStoreTest.java
@@ -101,8 +101,9 @@ private static void assertExpectedFacts(Iterable<Fact> facts, String expectedFir
                 + "com.google.common.truth.TestCorrespondences\\$NullPointerExceptionFromWithin10Of"
                 // some whitespace:
                 + "\\s+"
-                // the start of a stack trace, with the correct class:
-                + "at com\\.google\\.common\\.truth\\.TestCorrespondences"
+                // the start of a stack trace, optionally with the module name and version,
+                // and the correct class:
+                + "at (?:[^/]+/)?com\\.google\\.common\\.truth\\.TestCorrespondences"
                 // the rest of the stack trace, which we don't validate (and may contain newlines):
                 + "(.|\\n)*"
                 // the expected separator
diff --git a/extensions/java8/pom.xml b/extensions/java8/pom.xml
index b6f38c544..bcbb2ba42 100644
--- a/extensions/java8/pom.xml
+++ b/extensions/java8/pom.xml
@@ -7,7 +7,7 @@
   <parent>
     <groupId>com.google.truth.extensions</groupId>
     <artifactId>truth-extensions-parent</artifactId>
-    <version>HEAD-SNAPSHOT</version>
+    <version>999.0.0-SNAPSHOT</version>
   </parent>
   <artifactId>truth-java8-extension</artifactId>
   <name>Obsolete Truth Extension for Java8</name>
diff --git a/extensions/liteproto/pom.xml b/extensions/liteproto/pom.xml
index a70faa5d8..21dea4bc2 100644
--- a/extensions/liteproto/pom.xml
+++ b/extensions/liteproto/pom.xml
@@ -7,7 +7,7 @@
   <parent>
     <groupId>com.google.truth.extensions</groupId>
     <artifactId>truth-extensions-parent</artifactId>
-    <version>HEAD-SNAPSHOT</version>
+    <version>999.0.0-SNAPSHOT</version>
   </parent>
   <artifactId>truth-liteproto-extension</artifactId>
   <name>Truth Extension for Lite Protocol Buffers</name>
diff --git a/extensions/pom.xml b/extensions/pom.xml
index a3af92922..f5549cf66 100644
--- a/extensions/pom.xml
+++ b/extensions/pom.xml
@@ -7,7 +7,7 @@
   <parent>
     <groupId>com.google.truth</groupId>
     <artifactId>truth-parent</artifactId>
-    <version>HEAD-SNAPSHOT</version>
+    <version>999.0.0-SNAPSHOT</version>
   </parent>
   <groupId>com.google.truth.extensions</groupId>
   <artifactId>truth-extensions-parent</artifactId>
diff --git a/extensions/proto/pom.xml b/extensions/proto/pom.xml
index d52855799..649ef78c3 100644
--- a/extensions/proto/pom.xml
+++ b/extensions/proto/pom.xml
@@ -7,7 +7,7 @@
   <parent>
     <groupId>com.google.truth.extensions</groupId>
     <artifactId>truth-extensions-parent</artifactId>
-    <version>HEAD-SNAPSHOT</version>
+    <version>999.0.0-SNAPSHOT</version>
   </parent>
   <artifactId>truth-proto-extension</artifactId>
   <name>Truth Extension for Protocol Buffers</name>
diff --git a/extensions/re2j/pom.xml b/extensions/re2j/pom.xml
index 6ca4180ce..ae497198c 100644
--- a/extensions/re2j/pom.xml
+++ b/extensions/re2j/pom.xml
@@ -7,7 +7,7 @@
   <parent>
     <groupId>com.google.truth.extensions</groupId>
     <artifactId>truth-extensions-parent</artifactId>
-    <version>HEAD-SNAPSHOT</version>
+    <version>999.0.0-SNAPSHOT</version>
   </parent>
   <artifactId>truth-re2j-extension</artifactId>
   <name>Truth Extension for RE2J</name>
diff --git a/pom.xml b/pom.xml
index d23431246..b2bad88c0 100644
--- a/pom.xml
+++ b/pom.xml
@@ -6,7 +6,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.google.truth</groupId>
   <artifactId>truth-parent</artifactId>
-  <version>HEAD-SNAPSHOT</version>
+  <version>999.0.0-SNAPSHOT</version>
   <packaging>pom</packaging>
   <name>Truth (Parent)</name>
   <properties>
@@ -249,6 +249,7 @@
             <additionalOptions>
               <additionalOption>-Xdoclint:-html ${conditionalJavadoc9PlusOptions}</additionalOption>
             </additionalOptions>
+            <legacyMode>true</legacyMode>
             <doctitle>Truth ${project.version}</doctitle>
             <windowtitle>Truth ${project.version}</windowtitle>
             <quiet>true</quiet>