diff --git a/apps/cli/src/test/kotlin/dev/diff2test/android/cli/D2tConfigTest.kt b/apps/cli/src/test/kotlin/dev/diff2test/android/cli/D2tConfigTest.kt
index 023acc9..d742ea8 100644
--- a/apps/cli/src/test/kotlin/dev/diff2test/android/cli/D2tConfigTest.kt
+++ b/apps/cli/src/test/kotlin/dev/diff2test/android/cli/D2tConfigTest.kt
@@ -119,6 +119,27 @@ class D2tConfigTest {
         assertContains(report, "Supported now: yes")
     }
 
+    @Test
+    fun `defaults anthropic config to native messages protocol`() {
+        val configFile = Files.createTempFile("d2t-anthropic-config", ".toml")
+        Files.writeString(
+            configFile,
+            """
+            [ai]
+            provider = "anthropic"
+            """.trimIndent(),
+        )
+        val loadResult = loadConfig(configFile)
+        val resolved = resolveAiConfiguration(loadResult, mapOf("ANTHROPIC_API_KEY" to "sk-ant"))
+
+        assertEquals(AiProvider.ANTHROPIC, resolved?.provider)
+        assertEquals(AiProtocol.ANTHROPIC_MESSAGES, resolved?.protocol)
+        assertEquals("ANTHROPIC_API_KEY", resolved?.apiKeyEnv)
+        assertEquals("claude-sonnet-4-5", resolved?.model)
+        assertEquals("https://api.anthropic.com/v1", resolved?.baseUrl)
+        assertTrue(resolved?.supportedByGenerator == true)
+    }
+
     @Test
     fun `doctor report supports native gemini protocol`() {
         val loadResult = ConfigLoadResult.Loaded(
diff --git a/docs/providers/anthropic.md b/docs/providers/anthropic.md
new file mode 100644
index 0000000..c123f97
--- /dev/null
+++ b/docs/providers/anthropic.md
@@ -0,0 +1,37 @@
+# Anthropic Provider
+
+`d2t` supports the native Anthropic Messages API.
+
+## Config
+
+```toml
+[ai]
+enabled = true
+provider = "anthropic"
+protocol = "anthropic-messages"
+api_key_env = "ANTHROPIC_API_KEY"
+model = "claude-sonnet-4-5"
+base_url = "https://api.anthropic.com/v1"
+connect_timeout_seconds = 30
+request_timeout_seconds = 300
+```
+
+## Environment
+
+```bash
+export ANTHROPIC_API_KEY="..."
+```
+
+## Verify
+
+```bash
+d2t doctor
+d2t auto --ai
+```
+
+## Notes
+
+- `d2t` calls `POST /v1/messages`
+- authentication is sent with `x-api-key`
+- `anthropic-version: 2023-06-01` is always attached
+- use `--strict-ai` if you want the command to fail instead of falling back when AI generation is rejected
diff --git a/modules/test-generator/src/test/kotlin/dev/diff2test/android/testgenerator/OpenAiResponsesTestGeneratorTest.kt b/modules/test-generator/src/test/kotlin/dev/diff2test/android/testgenerator/OpenAiResponsesTestGeneratorTest.kt
index f4a26d3..fe5fbc7 100644
--- a/modules/test-generator/src/test/kotlin/dev/diff2test/android/testgenerator/OpenAiResponsesTestGeneratorTest.kt
+++ b/modules/test-generator/src/test/kotlin/dev/diff2test/android/testgenerator/OpenAiResponsesTestGeneratorTest.kt
@@ -26,9 +26,10 @@ import javax.net.ssl.SSLContext
 import javax.net.ssl.SSLParameters
 import javax.net.ssl.SSLSession
 import kotlin.test.Test
-import kotlin.test.assertEquals
 import kotlin.test.assertContains
+import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
+import kotlin.test.assertNotNull
 import kotlin.test.assertTrue
 
 class OpenAiResponsesTestGeneratorTest {
@@ -132,6 +133,28 @@ class OpenAiResponsesTestGeneratorTest {
         assertEquals(listOf("anthropic"), payload.warnings)
     }
 
+    @Test
+    fun `anthropic generator sends native headers to messages endpoint`() {
+        val capture = RequestCapture()
+        val generator = AnthropicMessagesTestGenerator(
+            config = AnthropicMessagesConfig(
+                apiKey = "sk-ant",
+                model = "claude-sonnet-4-5",
+                baseUrl = "https://api.anthropic.com/v1",
+            ),
+            httpClient = capturingHttpClient(capture, 200, anthropicResponseBody()),
+        )
+
+        val bundle = generator.generate(plan(), context(), analysis())
+
+        assertContains(bundle.files.single().content, "class SignUpViewModelGeneratedTest")
+        val request = assertNotNull(capture.request)
+        assertEquals("https://api.anthropic.com/v1/messages", request.uri().toString())
+        assertEquals("sk-ant", request.headers().firstValue("x-api-key").orElse(null))
+        assertEquals("2023-06-01", request.headers().firstValue("anthropic-version").orElse(null))
+        assertEquals("application/json", request.headers().firstValue("Accept").orElse(null))
+    }
+
     @Test
     fun `extracts structured payload from chat completions response body`() {
         val responseBody = """
@@ -588,7 +611,19 @@ class OpenAiResponsesTestGeneratorTest {
         )
     }
 
+    private data class RequestCapture(
+        var request: HttpRequest? = null,
+    )
+
     private fun fakeHttpClient(statusCode: Int, body: String): HttpClient {
+        return capturingHttpClient(RequestCapture(), statusCode, body)
+    }
+
+    private fun capturingHttpClient(
+        capture: RequestCapture,
+        statusCode: Int,
+        body: String,
+    ): HttpClient {
         return object : HttpClient() {
             override fun cookieHandler(): Optional<CookieHandler> = Optional.empty()
             override fun connectTimeout(): Optional<Duration> = Optional.empty()
@@ -603,8 +638,13 @@ class OpenAiResponsesTestGeneratorTest {
                 request: HttpRequest?,
                 responseBodyHandler: HttpResponse.BodyHandler<T>?,
             ): HttpResponse<T> {
+                capture.request = request
                 @Suppress("UNCHECKED_CAST")
-                return fakeResponse(statusCode, body) as HttpResponse<T>
+                return fakeResponse(
+                    statusCode = statusCode,
+                    body = body,
+                    uri = request?.uri()?.toString() ?: "http://127.0.0.1:12345/responses",
+                ) as HttpResponse<T>
             }
 
             override fun <T : Any?> sendAsync(
@@ -624,16 +664,27 @@ class OpenAiResponsesTestGeneratorTest {
         }
     }
 
-    private fun fakeResponse(statusCode: Int, body: String): HttpResponse<String> {
+    private fun fakeResponse(statusCode: Int, body: String, uri: String): HttpResponse<String> {
         return object : HttpResponse<String> {
             override fun statusCode(): Int = statusCode
-            override fun request(): HttpRequest = HttpRequest.newBuilder().uri(URI.create("http://127.0.0.1:12345/responses")).build()
+            override fun request(): HttpRequest = HttpRequest.newBuilder().uri(URI.create(uri)).build()
             override fun previousResponse(): Optional<HttpResponse<String>> = Optional.empty()
             override fun headers(): HttpHeaders = HttpHeaders.of(emptyMap()) { _, _ -> true }
             override fun body(): String = body
             override fun sslSession(): Optional<SSLSession> = Optional.empty()
-            override fun uri(): URI = URI.create("http://127.0.0.1:12345/responses")
+            override fun uri(): URI = URI.create(uri)
             override fun version(): HttpClient.Version = HttpClient.Version.HTTP_1_1
         }
     }
+
+    private fun anthropicResponseBody(): String = """
+        {
+          "content": [
+            {
+              "type": "text",
+              "text": "{\"content\":\"package com.example.auth\\n\\nclass SignUpViewModelGeneratedTest\",\"warnings\":[]}"
+            }
+          ]
+        }
+    """.trimIndent()
 }