diff --git a/src/main/resources/META-INF/rewrite/spring-boot-40-modular-starters.yml b/src/main/resources/META-INF/rewrite/spring-boot-40-modular-starters.yml
index 1d51573a8..824ad9291 100644
--- a/src/main/resources/META-INF/rewrite/spring-boot-40-modular-starters.yml
+++ b/src/main/resources/META-INF/rewrite/spring-boot-40-modular-starters.yml
@@ -102,6 +102,21 @@ recipeList:
       version: 4.0.x
       scope: test
       onlyIfUsing: org.springframework.test.web.servlet.MockMvc
+  # @WebFluxTest slice; keyed on specific types rather than the package, since the SB3 package's WebTestClient types belong to spring-boot-webtestclient and also serve MockMvc-backed tests
+  - org.openrewrite.java.dependencies.AddDependency:
+      groupId: org.springframework.boot
+      artifactId: spring-boot-starter-webflux-test
+      acceptTransitive: true
+      version: 4.0.x
+      scope: test
+      onlyIfUsing: org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest
+  - org.openrewrite.java.dependencies.AddDependency:
+      groupId: org.springframework.boot
+      artifactId: spring-boot-starter-webflux-test
+      acceptTransitive: true
+      version: 4.0.x
+      scope: test
+      onlyIfUsing: org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebFlux
   - org.openrewrite.java.dependencies.AddDependency:
       groupId: org.springframework.boot
       artifactId: spring-boot-starter-restclient
@@ -405,6 +420,16 @@ recipeList:
       oldPackageName: org.springframework.boot.test.autoconfigure.web.servlet
       newPackageName: org.springframework.boot.webmvc.test.autoconfigure
       recursive: true
+  # spring-boot-webflux-test: the @WebFluxTest slice, type-by-type since the WebTestClient types below share the SB3 package but move to spring-boot-webtestclient instead
+  - org.openrewrite.java.ChangeType:
+      oldFullyQualifiedTypeName: org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest
+      newFullyQualifiedTypeName: org.springframework.boot.webflux.test.autoconfigure.WebFluxTest
+  - org.openrewrite.java.ChangeType:
+      oldFullyQualifiedTypeName: org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebFlux
+      newFullyQualifiedTypeName: org.springframework.boot.webflux.test.autoconfigure.AutoConfigureWebFlux
+  - org.openrewrite.java.ChangeType:
+      oldFullyQualifiedTypeName: org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTypeExcludeFilter
+      newFullyQualifiedTypeName: org.springframework.boot.webflux.test.autoconfigure.WebFluxTypeExcludeFilter
   # spring-boot-webtestclient (originating from spring-boot-test-autoconfigure and spring-boot-test)
   - org.openrewrite.java.ChangeType:
       oldFullyQualifiedTypeName: org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient
diff --git a/src/test/java/org/openrewrite/java/spring/boot4/MigrateToModularStartersTest.java b/src/test/java/org/openrewrite/java/spring/boot4/MigrateToModularStartersTest.java
index b55d49287..3251a9a91 100644
--- a/src/test/java/org/openrewrite/java/spring/boot4/MigrateToModularStartersTest.java
+++ b/src/test/java/org/openrewrite/java/spring/boot4/MigrateToModularStartersTest.java
@@ -333,6 +333,167 @@ class A {
         );
     }
 
+    @Nested
+    class WebFluxTestSlice {
+
+        @Test
+        void addWebFluxTestStarterIfWebFluxTestIsUsedForTest() {
+            rewriteRun(
+              mavenProject("project",
+                //language=xml
+                pomXml(
+                  """
+                    <project>
+                        <modelVersion>4.0.0</modelVersion>
+                        <groupId>org.example</groupId>
+                        <artifactId>example</artifactId>
+                        <version>1.0-SNAPSHOT</version>
+                        <dependencies>
+                        </dependencies>
+                    </project>
+                    """,
+                  spec -> spec.after(pom -> assertThat(pom)
+                    .contains("<artifactId>spring-boot-starter-webflux-test</artifactId>")
+                    .contains("<scope>test</scope>")
+                    .containsPattern("<version>4\\.0\\.\\d+</version>")
+                    .actual())
+                ),
+                srcTestJava(
+                  //language=java
+                  java(
+                    """
+                      import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
+
+                      @WebFluxTest
+                      class GreetingControllerTest {
+                      }
+                      """,
+                    """
+                      import org.springframework.boot.webflux.test.autoconfigure.WebFluxTest;
+
+                      @WebFluxTest
+                      class GreetingControllerTest {
+                      }
+                      """
+                  )
+                )
+              )
+            );
+        }
+
+        @Test
+        void addWebFluxTestStarterIfAutoConfigureWebFluxIsUsedForTest() {
+            rewriteRun(
+              mavenProject("project",
+                //language=xml
+                pomXml(
+                  """
+                    <project>
+                        <modelVersion>4.0.0</modelVersion>
+                        <groupId>org.example</groupId>
+                        <artifactId>example</artifactId>
+                        <version>1.0-SNAPSHOT</version>
+                        <dependencies>
+                        </dependencies>
+                    </project>
+                    """,
+                  spec -> spec.after(pom -> assertThat(pom)
+                    .contains("<artifactId>spring-boot-starter-webflux-test</artifactId>")
+                    .contains("<scope>test</scope>")
+                    .containsPattern("<version>4\\.0\\.\\d+</version>")
+                    .actual())
+                ),
+                srcTestJava(
+                  //language=java
+                  java(
+                    """
+                      import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebFlux;
+
+                      @AutoConfigureWebFlux
+                      class GreetingIntegrationTest {
+                      }
+                      """,
+                    """
+                      import org.springframework.boot.webflux.test.autoconfigure.AutoConfigureWebFlux;
+
+                      @AutoConfigureWebFlux
+                      class GreetingIntegrationTest {
+                      }
+                      """
+                  )
+                )
+              )
+            );
+        }
+
+        @Test
+        void doesNotAddWebFluxTestStarterForAutoConfigureWebTestClientUsage() {
+            rewriteRun(
+              mavenProject("project",
+                //language=xml
+                pomXml(
+                  """
+                    <project>
+                        <modelVersion>4.0.0</modelVersion>
+                        <groupId>org.example</groupId>
+                        <artifactId>example</artifactId>
+                        <version>1.0-SNAPSHOT</version>
+                        <dependencies>
+                        </dependencies>
+                    </project>
+                    """
+                ),
+                srcTestJava(
+                  //language=java
+                  java(
+                    """
+                      import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient;
+
+                      @AutoConfigureWebTestClient
+                      class ApiIntegrationTest {
+                      }
+                      """,
+                    """
+                      import org.springframework.boot.webtestclient.autoconfigure.AutoConfigureWebTestClient;
+
+                      @AutoConfigureWebTestClient
+                      class ApiIntegrationTest {
+                      }
+                      """
+                  )
+                )
+              )
+            );
+        }
+
+        @Test
+        void migrateWebFluxTestSliceTypes() {
+            rewriteRun(
+              //language=java
+              java(
+                """
+                  import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebFlux;
+                  import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTypeExcludeFilter;
+
+                  @AutoConfigureWebFlux
+                  class GreetingIntegrationTest {
+                      WebFluxTypeExcludeFilter filter;
+                  }
+                  """,
+                """
+                  import org.springframework.boot.webflux.test.autoconfigure.AutoConfigureWebFlux;
+                  import org.springframework.boot.webflux.test.autoconfigure.WebFluxTypeExcludeFilter;
+
+                  @AutoConfigureWebFlux
+                  class GreetingIntegrationTest {
+                      WebFluxTypeExcludeFilter filter;
+                  }
+                  """
+              )
+            );
+        }
+    }
+
     @Nested
     class MigrateActuateHealthPackage implements RewriteTest {
         @Override