diff --git a/.github/workflows/auto-spotless-check.yml b/.github/workflows/auto-spotless-check.yml
index 5226b6728..422e4fa44 100644
--- a/.github/workflows/auto-spotless-check.yml
+++ b/.github/workflows/auto-spotless-check.yml
@@ -22,7 +22,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
diff --git a/.github/workflows/build-common.yml b/.github/workflows/build-common.yml
index a792503d9..20493a46c 100644
--- a/.github/workflows/build-common.yml
+++ b/.github/workflows/build-common.yml
@@ -27,7 +27,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
@@ -48,7 +48,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
@@ -106,7 +106,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 2a465c746..1820bd005 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -32,7 +32,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index f793ebbf7..f2dfba7f0 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -38,12 +38,12 @@ jobs:
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
-      - name: Set up Java 17
+      - name: Set up Java
         if: matrix.language == 'java'
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up gradle
         if: matrix.language == 'java'
diff --git a/.github/workflows/copilot-setup-steps.yml b/.github/workflows/copilot-setup-steps.yml
index 53258f82a..000e992cf 100644
--- a/.github/workflows/copilot-setup-steps.yml
+++ b/.github/workflows/copilot-setup-steps.yml
@@ -25,7 +25,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
diff --git a/.github/workflows/owasp-dependency-check-daily.yml b/.github/workflows/owasp-dependency-check-daily.yml
index ce160b330..664a6a214 100644
--- a/.github/workflows/owasp-dependency-check-daily.yml
+++ b/.github/workflows/owasp-dependency-check-daily.yml
@@ -21,7 +21,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Increase gradle daemon heap size
         run: |
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 097433535..751ef279a 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -86,7 +86,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
@@ -234,7 +234,7 @@ jobs:
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d6e0a0a36..3c90039e4 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -17,7 +17,7 @@ Pull requests for bug fixes are always welcome!
 
 ## Building and Testing
 
-While most modules target Java 8, building this project requires Java 17 or higher.
+While most modules target Java 8, building this project requires Java 21 or higher.
 
 To build the project:
 
diff --git a/aws-resources/src/main/java/io/opentelemetry/contrib/aws/resource/SimpleHttpClient.java b/aws-resources/src/main/java/io/opentelemetry/contrib/aws/resource/SimpleHttpClient.java
index f78719d99..ba9bf7517 100644
--- a/aws-resources/src/main/java/io/opentelemetry/contrib/aws/resource/SimpleHttpClient.java
+++ b/aws-resources/src/main/java/io/opentelemetry/contrib/aws/resource/SimpleHttpClient.java
@@ -27,7 +27,6 @@
 import okhttp3.Request;
 import okhttp3.RequestBody;
 import okhttp3.Response;
-import okhttp3.ResponseBody;
 
 /** A simple HTTP client based on OkHttp. Not meant for high throughput. */
 final class SimpleHttpClient {
@@ -83,8 +82,7 @@ public String fetchString(
                 + response.message());
         return "";
       }
-      ResponseBody body = response.body();
-      return body != null ? body.string() : "";
+      return response.body().string();
     } catch (IOException e) {
       logger.log(FINE, "SimpleHttpClient fetch string failed.", e);
     }
diff --git a/aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/XraySamplerClient.java b/aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/XraySamplerClient.java
index 84dbd0144..ef47ba725 100644
--- a/aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/XraySamplerClient.java
+++ b/aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/XraySamplerClient.java
@@ -46,7 +46,6 @@
 import okhttp3.Request;
 import okhttp3.RequestBody;
 import okhttp3.Response;
-import okhttp3.ResponseBody;
 
 final class XraySamplerClient {
 
@@ -125,11 +124,7 @@ private static String readResponse(Response response, String endpoint) throws IO
       return "";
     }
 
-    ResponseBody body = response.body();
-    if (body != null) {
-      return body.string();
-    }
-    return "";
+    return response.body().string();
   }
 
   // Visible for testing
diff --git a/buildSrc/src/main/kotlin/otel.errorprone-conventions.gradle.kts b/buildSrc/src/main/kotlin/otel.errorprone-conventions.gradle.kts
index 113576db3..4502a84c6 100644
--- a/buildSrc/src/main/kotlin/otel.errorprone-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/otel.errorprone-conventions.gradle.kts
@@ -50,7 +50,6 @@ tasks {
 
         // TODO (trask) use animal sniffer
         disable("Java8ApiChecker")
-        disable("AndroidJdkLibsChecker")
 
         // apparently disabling android doesn't disable this
         disable("StaticOrDefaultInterfaceMethod")
diff --git a/buildSrc/src/main/kotlin/otel.java-conventions.gradle.kts b/buildSrc/src/main/kotlin/otel.java-conventions.gradle.kts
index 70bd9687b..add3d03a0 100644
--- a/buildSrc/src/main/kotlin/otel.java-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/otel.java-conventions.gradle.kts
@@ -18,7 +18,7 @@ group = "io.opentelemetry.contrib"
 base.archivesName.set("opentelemetry-${project.name}")
 
 // Version to use to compile code and run tests.
-val DEFAULT_JAVA_VERSION = JavaVersion.VERSION_17
+val DEFAULT_JAVA_VERSION = JavaVersion.VERSION_21
 
 java {
   toolchain {
@@ -60,6 +60,7 @@ tasks {
       if (name.contains("Test")) {
         // serialVersionUI is basically guaranteed to be useless in tests
         compilerArgs.add("-Xlint:-serial")
+        compilerArgs.add("-Xlint:-this-escape")
       }
     }
   }
diff --git a/consistent-sampling/src/main/java/io/opentelemetry/contrib/sampler/consistent56/ConsistentVariableThresholdSampler.java b/consistent-sampling/src/main/java/io/opentelemetry/contrib/sampler/consistent56/ConsistentVariableThresholdSampler.java
index 1558e961c..9d356d49b 100644
--- a/consistent-sampling/src/main/java/io/opentelemetry/contrib/sampler/consistent56/ConsistentVariableThresholdSampler.java
+++ b/consistent-sampling/src/main/java/io/opentelemetry/contrib/sampler/consistent56/ConsistentVariableThresholdSampler.java
@@ -16,7 +16,7 @@ public class ConsistentVariableThresholdSampler extends ConsistentThresholdSampl
   private volatile String description = "";
 
   protected ConsistentVariableThresholdSampler(double samplingProbability) {
-    setSamplingProbability(samplingProbability);
+    updateSamplingProbability(samplingProbability);
   }
 
   @Override
@@ -30,6 +30,10 @@ public long getThreshold() {
   }
 
   public void setSamplingProbability(double samplingProbability) {
+    updateSamplingProbability(samplingProbability);
+  }
+
+  private void updateSamplingProbability(double samplingProbability) {
     long threshold = calculateThreshold(samplingProbability);
     checkThreshold(threshold);
     this.threshold = threshold;
diff --git a/dependencyManagement/build.gradle.kts b/dependencyManagement/build.gradle.kts
index ec7cdec0e..0bcc53732 100644
--- a/dependencyManagement/build.gradle.kts
+++ b/dependencyManagement/build.gradle.kts
@@ -27,8 +27,8 @@ dependencies {
     api("com.google.auto.service:auto-service-annotations:1.1.1")
     api("com.google.auto.value:auto-value:1.11.0")
     api("com.google.auto.value:auto-value-annotations:1.11.0")
-    api("com.google.errorprone:error_prone_annotations:2.42.0")
-    api("com.google.errorprone:error_prone_core:2.42.0")
+    api("com.google.errorprone:error_prone_annotations:2.43.0")
+    api("com.google.errorprone:error_prone_core:2.43.0")
     api("io.github.netmikey.logunit:logunit-jul:2.0.0")
     api("io.opentelemetry.proto:opentelemetry-proto:1.8.0-alpha")
     api("io.prometheus:simpleclient:0.16.0")
diff --git a/disk-buffering/build.gradle.kts b/disk-buffering/build.gradle.kts
index c36d73588..b3e775be0 100644
--- a/disk-buffering/build.gradle.kts
+++ b/disk-buffering/build.gradle.kts
@@ -63,6 +63,12 @@ tasks.named<ShadowJar>("shadowJar") {
   mustRunAfter("jar")
 }
 
+tasks {
+  test {
+    dependsOn("shadowJar")
+  }
+}
+
 // The javadoc from wire's generated classes has errors that make the task that generates the "javadoc" artifact to fail. This
 // makes the javadoc task to ignore those generated classes.
 tasks.withType(Javadoc::class.java) {
@@ -75,3 +81,11 @@ tasks.withType(Javadoc::class.java) {
 tasks.named("sourcesJar", Jar::class.java) {
   duplicatesStrategy = DuplicatesStrategy.EXCLUDE
 }
+
+tasks.withType<JavaCompile>().configureEach {
+  with(options) {
+    // classes generated from proto trigger
+    // warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
+    compilerArgs.add("-Xlint:-serial")
+  }
+}
diff --git a/inferred-spans/src/main/java/io/opentelemetry/contrib/inferredspans/internal/SamplingProfiler.java b/inferred-spans/src/main/java/io/opentelemetry/contrib/inferredspans/internal/SamplingProfiler.java
index 27d0e5305..90a2bc250 100644
--- a/inferred-spans/src/main/java/io/opentelemetry/contrib/inferredspans/internal/SamplingProfiler.java
+++ b/inferred-spans/src/main/java/io/opentelemetry/contrib/inferredspans/internal/SamplingProfiler.java
@@ -165,6 +165,7 @@ public class SamplingProfiler implements Runnable {
    * @param activationEventsFile activation events file, if {@literal null} a temp file will be used
    * @param jfrFile java flight recorder file, if {@literal null} a temp file will be used instead
    */
+  @SuppressWarnings("this-escape")
   public SamplingProfiler(
       InferredSpansConfiguration config,
       SpanAnchoredClock nanoClock,
diff --git a/opamp-client/build.gradle.kts b/opamp-client/build.gradle.kts
index 8abbbee65..767892572 100644
--- a/opamp-client/build.gradle.kts
+++ b/opamp-client/build.gradle.kts
@@ -1,6 +1,6 @@
 import java.io.FileOutputStream
 import java.io.InputStream
-import java.net.URL
+import java.net.URI
 
 plugins {
   id("otel.java-conventions")
@@ -38,6 +38,14 @@ wire {
   }
 }
 
+tasks.withType<JavaCompile>().configureEach {
+  with(options) {
+    // classes generated from proto trigger
+    // warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
+    compilerArgs.add("-Xlint:-serial")
+  }
+}
+
 abstract class DownloadAndExtractOpampProtos @Inject constructor(
   private val archiveOps: ArchiveOperations,
   private val fileOps: FileSystemOperations,
@@ -54,7 +62,7 @@ abstract class DownloadAndExtractOpampProtos @Inject constructor(
 
   @TaskAction
   fun execute() {
-    val url = URL(zipUrl.get())
+    val url = URI.create(zipUrl.get()).toURL()
     downloadedZipFile.get().asFile.parentFile.mkdirs()
 
     url.openStream().use { input: InputStream ->