diff --git a/CHANGES.md b/CHANGES.md
index 2d078e7..e9fce25 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,7 @@
+## Unreleased
+
+* Added `Format` constants for the media types `convert` accepts, including JPEG XL (`image/jxl`).
+
 ## 1.8.9
 * Upgraded dependencies (okio 3.12.0, gson 2.13.1, commons-codec 1.21.0)
 * Upgraded all Maven plugins to latest stable versions
diff --git a/src/main/java/com/tinify/Format.java b/src/main/java/com/tinify/Format.java
new file mode 100644
index 0000000..c383186
--- /dev/null
+++ b/src/main/java/com/tinify/Format.java
@@ -0,0 +1,45 @@
+package com.tinify;
+
+/**
+ * Media types that images can be converted to.
+ *
+ * <p>Use these constants with {@link Source#convert(Options)}:
+ *
+ * <pre>{@code
+ * Tinify.fromFile("input.png")
+ *       .convert(new Options().with("type", Format.JXL))
+ *       .toFile("output.jxl");
+ * }</pre>
+ *
+ * <p>Multiple types may be supplied, in which case the API returns the
+ * smallest result:
+ *
+ * <pre>{@code
+ * new Options().with("type", new String[]{Format.JXL, Format.WEBP});
+ * }</pre>
+ */
+public final class Format {
+    /** WebP, {@code image/webp}. */
+    public static final String WEBP = "image/webp";
+
+    /** PNG, {@code image/png}. */
+    public static final String PNG = "image/png";
+
+    /** JPEG, {@code image/jpeg}. */
+    public static final String JPEG = "image/jpeg";
+
+    /** JPEG, {@code image/jpg}. An alias of {@link #JPEG}. */
+    public static final String JPG = "image/jpg";
+
+    /** AVIF, {@code image/avif}. */
+    public static final String AVIF = "image/avif";
+
+    /** JPEG XL, {@code image/jxl}. */
+    public static final String JXL = "image/jxl";
+
+    /** Wildcard, {@code &#42;/&#42;}. Returns the smallest of the supported types. */
+    public static final String ANY = "*/*";
+
+    private Format() {
+    }
+}
diff --git a/src/test/java/com/tinify/FormatTest.java b/src/test/java/com/tinify/FormatTest.java
new file mode 100644
index 0000000..acd94eb
--- /dev/null
+++ b/src/test/java/com/tinify/FormatTest.java
@@ -0,0 +1,34 @@
+package com.tinify;
+
+import org.junit.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.equalTo;
+
+public class FormatTest {
+    @Test
+    public void formatShouldExposeSupportedMediaTypes() {
+        assertThat(Format.WEBP, is(equalTo("image/webp")));
+        assertThat(Format.PNG, is(equalTo("image/png")));
+        assertThat(Format.JPEG, is(equalTo("image/jpeg")));
+        assertThat(Format.JPG, is(equalTo("image/jpg")));
+        assertThat(Format.AVIF, is(equalTo("image/avif")));
+        assertThat(Format.JXL, is(equalTo("image/jxl")));
+        assertThat(Format.ANY, is(equalTo("*/*")));
+    }
+
+    @Test
+    public void convertWithFormatShouldSerializeMediaType() {
+        Options options = new Options().with("convert", new Options().with("type", Format.JXL));
+        assertThat(options.toJson(), is(equalTo("{\"convert\":{\"type\":\"image/jxl\"}}")));
+    }
+
+    @Test
+    public void convertWithMultipleFormatsShouldSerializeMediaTypes() {
+        Options options = new Options().with("convert",
+                new Options().with("type", new String[]{Format.JXL, Format.WEBP}));
+        assertThat(options.toJson(),
+                is(equalTo("{\"convert\":{\"type\":[\"image/jxl\",\"image/webp\"]}}")));
+    }
+}