diff --git a/.gitmodules b/.gitmodules
index ce2abc73..c4b2a4f8 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -12,3 +12,7 @@
 	path = test-server/php-v3-server/local-php-sdk
 	url = git@github.com:aws/private-aws-sdk-php-staging.git
 	branch = s3ec/improved
+[submodule "test-server/java-v3-server/s3ec-staging"]
+	path = test-server/java-v3-server/s3ec-staging
+	url = git@github.com:aws/private-amazon-s3-encryption-client-java-staging.git
+	branch = s3ec/transitional
diff --git a/test-server/java-v3-server/Makefile b/test-server/java-v3-server/Makefile
index 1e0dc763..b93dd2ce 100644
--- a/test-server/java-v3-server/Makefile
+++ b/test-server/java-v3-server/Makefile
@@ -1,11 +1,17 @@
 # Makefile for S3 Encryption Client Testing
 
-.PHONY: start-server stop-server wait-for-server
+.PHONY: start-server stop-server wait-for-server build-s3ec
 
 PID_FILE := server.pid
 PORT := 8080
 
-start-server:
+build-s3ec:
+	@echo "Building S3EC from source..."
+	cd s3ec-staging && mvn --batch-mode -no-transfer-progress clean compile
+	cd s3ec-staging && mvn -B -ntp install -DskipTests
+	@echo "S3EC build completed."
+
+start-server: build-s3ec
 	@echo "Starting Java V3 server..."
 	AWS_ACCESS_KEY_ID="$$AWS_ACCESS_KEY_ID" \
 	AWS_SECRET_ACCESS_KEY="$$AWS_SECRET_ACCESS_KEY" \
diff --git a/test-server/java-v3-server/build.gradle.kts b/test-server/java-v3-server/build.gradle.kts
index ca793e56..b874d8e2 100644
--- a/test-server/java-v3-server/build.gradle.kts
+++ b/test-server/java-v3-server/build.gradle.kts
@@ -13,8 +13,8 @@ dependencies {
     implementation("software.amazon.smithy.java:server-netty:$smithyJavaVersion")
     implementation("software.amazon.smithy.java:aws-server-restjson:$smithyJavaVersion")
 
-    compileOnly("software.amazon.awssdk:aws-sdk-java:2.31.66")
-    implementation("software.amazon.encryption.s3:amazon-s3-encryption-client-java:3.3.5")
+    // S3EC from local Maven repository (installed by mvn install)
+    implementation("software.amazon.encryption.s3:amazon-s3-encryption-client-java:3.4.0-SNAPSHOT")
 }
 
 // Use that application plugin to start the service via the `run` task.
diff --git a/test-server/java-v3-server/s3ec-staging b/test-server/java-v3-server/s3ec-staging
new file mode 160000
index 00000000..c572d958
--- /dev/null
+++ b/test-server/java-v3-server/s3ec-staging
@@ -0,0 +1 @@
+Subproject commit c572d9587ee934aad6a2fe8091a72080846d32af