diff --git a/openai-java-core/src/main/kotlin/com/openai/models/audio/AudioResponseFormat.kt b/openai-java-core/src/main/kotlin/com/openai/models/audio/AudioResponseFormat.kt
index fa2a75a45..394c6cab1 100644
--- a/openai-java-core/src/main/kotlin/com/openai/models/audio/AudioResponseFormat.kt
+++ b/openai-java-core/src/main/kotlin/com/openai/models/audio/AudioResponseFormat.kt
@@ -166,6 +166,7 @@ class AudioResponseFormat @JsonCreator private constructor(private val value: Js
             SRT -> false
             VERBOSE_JSON -> true
             VTT -> false
+            DIARIZED_JSON -> true
             else -> false
         }
 
diff --git a/openai-java-core/src/test/kotlin/com/openai/models/audio/AudioResponseFormatTest.kt b/openai-java-core/src/test/kotlin/com/openai/models/audio/AudioResponseFormatTest.kt
new file mode 100644
index 000000000..780d70174
--- /dev/null
+++ b/openai-java-core/src/test/kotlin/com/openai/models/audio/AudioResponseFormatTest.kt
@@ -0,0 +1,54 @@
+// File generated from our OpenAPI spec by Stainless.
+
+package com.openai.models.audio
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+internal class AudioResponseFormatTest {
+
+    /**
+     * Regression test for [#652](https://github.com/openai/openai-java/issues/652).
+     *
+     * Each value of [AudioResponseFormat.Known] is enumerated explicitly so that adding a new
+     * format also requires adding it to this test. That makes it impossible to introduce a new JSON
+     * format without consciously deciding whether [AudioResponseFormat.isJson] should return `true`
+     * for it — the bug that caused `DIARIZED_JSON` responses to be parsed as plain text and stashed
+     * in `TranscriptionCreateResponse.transcription.text` instead of populating
+     * `TranscriptionCreateResponse.diarized`.
+     */
+    @Test
+    fun isJson_returnsTrue_forEveryJsonResponseFormat() {
+        for (known in AudioResponseFormat.Known.values()) {
+            val format = AudioResponseFormat.of(known.toString().lowercase())
+            val expected =
+                when (known) {
+                    AudioResponseFormat.Known.JSON -> true
+                    AudioResponseFormat.Known.TEXT -> false
+                    AudioResponseFormat.Known.SRT -> false
+                    AudioResponseFormat.Known.VERBOSE_JSON -> true
+                    AudioResponseFormat.Known.VTT -> false
+                    AudioResponseFormat.Known.DIARIZED_JSON -> true
+                }
+            assertThat(format.isJson())
+                .withFailMessage(
+                    "AudioResponseFormat.$known.isJson() returned %s but expected %s",
+                    format.isJson(),
+                    expected,
+                )
+                .isEqualTo(expected)
+        }
+    }
+
+    /**
+     * Pinning [#652](https://github.com/openai/openai-java/issues/652) directly: a SDK consumer
+     * that requests `diarized_json` and feeds the value back through [AudioResponseFormat.of] must
+     * see [AudioResponseFormat.isJson] return `true`, otherwise the response body is treated as
+     * plain text by the transcription parser.
+     */
+    @Test
+    fun diarizedJson_isReportedAsJson() {
+        assertThat(AudioResponseFormat.DIARIZED_JSON.isJson()).isTrue()
+        assertThat(AudioResponseFormat.of("diarized_json").isJson()).isTrue()
+    }
+}