diff --git a/anthropic-java-core/build.gradle.kts b/anthropic-java-core/build.gradle.kts
index b1f8a0d71..3b499ddcb 100644
--- a/anthropic-java-core/build.gradle.kts
+++ b/anthropic-java-core/build.gradle.kts
@@ -89,3 +89,14 @@ dependencies {
     testImplementation(libs.mockito.junit.jupiter)
     testImplementation(libs.mockito.kotlin)
 }
+
+// GraalVM Native Image needs to be told what Jackson and Kotlin reflection call reflectively. The
+// metadata is generated from the compiled classes so it stays complete as the API grows.
+val nativeImageMetadata by tasks.registering(NativeImageMetadata::class) {
+    classesDirs.from(sourceSets.main.map { it.output.classesDirs })
+    runtimeClasspath.from(configurations.runtimeClasspath)
+    groupId = project.group.toString()
+    artifactId = project.name
+    outputDirectory = layout.buildDirectory.dir("generated/native-image")
+}
+sourceSets.main { resources.srcDir(nativeImageMetadata) }
diff --git a/buildSrc/src/main/kotlin/NativeImageMetadata.kt b/buildSrc/src/main/kotlin/NativeImageMetadata.kt
new file mode 100644
index 000000000..9f0445357
--- /dev/null
+++ b/buildSrc/src/main/kotlin/NativeImageMetadata.kt
@@ -0,0 +1,173 @@
+import groovy.json.JsonOutput
+import java.lang.reflect.AnnotatedElement
+import java.lang.reflect.Constructor
+import java.lang.reflect.Modifier
+import java.net.URLClassLoader
+import org.gradle.api.DefaultTask
+import org.gradle.api.file.ConfigurableFileCollection
+import org.gradle.api.file.DirectoryProperty
+import org.gradle.api.provider.Property
+import org.gradle.api.tasks.CacheableTask
+import org.gradle.api.tasks.Classpath
+import org.gradle.api.tasks.Input
+import org.gradle.api.tasks.OutputDirectory
+import org.gradle.api.tasks.TaskAction
+
+/**
+ * Writes the GraalVM Native Image reachability metadata that Jackson and Kotlin reflection need for
+ * a module's classes, at `META-INF/native-image/<group>/<name>/reflect-config.json` under
+ * [outputDirectory].
+ *
+ * It registers what `META-INF/proguard/anthropic-java-core.pro` keeps, read from the compiled
+ * classes so it covers every class without relying on what a test run happens to exercise:
+ * - every class, so Kotlin reflection can load the classes a `@Metadata` annotation names;
+ * - the constructors (including Kotlin's synthetic default-argument one), fields and annotated
+ *   methods of each class with a Jackson annotation, which Jackson calls reflectively; and
+ * - the no-argument constructor of each class that a Jackson annotation refers to (serializers,
+ *   deserializers and filters), which Jackson instantiates reflectively.
+ */
+@CacheableTask
+abstract class NativeImageMetadata : DefaultTask() {
+    @get:Classpath abstract val classesDirs: ConfigurableFileCollection
+
+    /** The classes that [classesDirs] refer to, so they load. */
+    @get:Classpath abstract val runtimeClasspath: ConfigurableFileCollection
+
+    @get:Input abstract val groupId: Property<String>
+
+    @get:Input abstract val artifactId: Property<String>
+
+    @get:OutputDirectory abstract val outputDirectory: DirectoryProperty
+
+    @TaskAction
+    fun generate() {
+        val classNames =
+            classesDirs.files
+                .flatMap { dir ->
+                    dir.walk()
+                        .filter { it.isFile && it.extension == "class" }
+                        .map { it.relativeTo(dir).invariantSeparatorsPath }
+                }
+                // Skip `module-info` and the multi-release copies of the same classes.
+                .filter { !it.startsWith("META-INF/") && !it.endsWith("module-info.class") }
+                .map { it.removeSuffix(".class").replace('/', '.') }
+                .toSortedSet()
+
+        val urls = (classesDirs + runtimeClasspath).map { it.toURI().toURL() }.toTypedArray()
+        val entries =
+            URLClassLoader(urls, ClassLoader.getPlatformClassLoader()).use { loader ->
+                val classes =
+                    classNames
+                        .map { Class.forName(it, false, loader) }
+                        .filter { !it.isAnonymousClass && !it.isLocalClass && !it.isSynthetic }
+                val entries = classes.associate { it.name to Entry(it.name) }.toSortedMap()
+
+                for (cls in classes) {
+                    val entry = entries.getValue(cls.name)
+                    val annotatedMethods = cls.declaredMethods.filter { it.hasJacksonAnnotation() }
+                    val hasJacksonAnnotation =
+                        cls.hasJacksonAnnotation() ||
+                            annotatedMethods.isNotEmpty() ||
+                            cls.declaredFields.any { it.hasJacksonAnnotation() } ||
+                            cls.declaredConstructors.any { constructor ->
+                                constructor.hasJacksonAnnotation() ||
+                                    constructor.parameterAnnotations.flatten().any {
+                                        it.isJackson()
+                                    }
+                            }
+                    if (hasJacksonAnnotation) {
+                        entry.allConstructorsAndFields = true
+                        annotatedMethods.forEach { entry.addMethod(it.name, it.parameterTypes) }
+                    }
+
+                    for (referenced in cls.referencedByJacksonAnnotations()) {
+                        val noArgConstructor = referenced.noArgConstructor() ?: continue
+                        entries
+                            .getOrPut(referenced.name) { Entry(referenced.name) }
+                            .addMethod("<init>", noArgConstructor.parameterTypes)
+                    }
+                }
+                entries.values.map { it.toJson() }
+            }
+
+        val file =
+            outputDirectory
+                .file(
+                    "META-INF/native-image/${groupId.get()}/${artifactId.get()}/reflect-config.json"
+                )
+                .get()
+                .asFile
+        file.parentFile.mkdirs()
+        file.writeText(JsonOutput.prettyPrint(JsonOutput.toJson(entries)) + "\n")
+    }
+
+    private class Entry(val name: String) {
+        var allConstructorsAndFields = false
+        private val methods = sortedMapOf<String, List<String>>()
+
+        fun addMethod(name: String, parameterTypes: Array<Class<*>>) {
+            val typeNames = parameterTypes.map { it.typeName }
+            methods["$name(${typeNames.joinToString()})"] = typeNames
+        }
+
+        fun toJson(): Map<String, Any> = buildMap {
+            // Only when the image can reach the class, so unused API types add nothing to it.
+            put("condition", mapOf("typeReachable" to name))
+            put("name", name)
+            if (allConstructorsAndFields) {
+                put("allDeclaredConstructors", true)
+                put("allDeclaredFields", true)
+                // Kotlin reflection looks the methods up to match them to functions and properties.
+                put("queryAllDeclaredMethods", true)
+            }
+            if (methods.isNotEmpty()) {
+                put(
+                    "methods",
+                    methods.map { (signature, parameterTypes) ->
+                        mapOf(
+                            "name" to signature.substringBefore('('),
+                            "parameterTypes" to parameterTypes,
+                        )
+                    },
+                )
+            }
+        }
+    }
+}
+
+private fun Annotation.isJackson() =
+    annotationClass.java.name.startsWith("com.fasterxml.jackson.annotation.") ||
+        annotationClass.java.name.startsWith("com.fasterxml.jackson.databind.annotation.")
+
+private fun AnnotatedElement.hasJacksonAnnotation() = declaredAnnotations.any { it.isJackson() }
+
+/** The classes that a non-default `Class` value of a Jackson annotation on [this] refers to. */
+private fun Class<*>.referencedByJacksonAnnotations(): Sequence<Class<*>> {
+    val annotations =
+        declaredAnnotations.asSequence() +
+            declaredMethods.asSequence().flatMap { it.declaredAnnotations.asSequence() } +
+            declaredFields.asSequence().flatMap { it.declaredAnnotations.asSequence() } +
+            declaredConstructors.asSequence().flatMap { constructor ->
+                constructor.declaredAnnotations.asSequence() +
+                    constructor.parameterAnnotations.asSequence().flatMap { it.asSequence() }
+            }
+    return annotations
+        .filter { it.isJackson() }
+        .flatMap { annotation ->
+            annotation.annotationClass.java.declaredMethods.asSequence().flatMap { element ->
+                val value = element.invoke(annotation)
+                if (value == element.defaultValue) {
+                    return@flatMap emptySequence()
+                }
+                when (value) {
+                    is Class<*> -> sequenceOf(value)
+                    is Array<*> -> value.asSequence().filterIsInstance<Class<*>>()
+                    else -> emptySequence()
+                }
+            }
+        }
+}
+
+private fun Class<*>.noArgConstructor(): Constructor<*>? =
+    if (isInterface || Modifier.isAbstract(modifiers)) null
+    else declaredConstructors.firstOrNull { it.parameterCount == 0 }