diff --git a/slack-base/src/main/java/com/hubspot/slack/client/methods/params/assistant/SetThreadStatusParamsIF.java b/slack-base/src/main/java/com/hubspot/slack/client/methods/params/assistant/SetThreadStatusParamsIF.java
index fe986005..1746fbac 100644
--- a/slack-base/src/main/java/com/hubspot/slack/client/methods/params/assistant/SetThreadStatusParamsIF.java
+++ b/slack-base/src/main/java/com/hubspot/slack/client/methods/params/assistant/SetThreadStatusParamsIF.java
@@ -1,15 +1,22 @@
 package com.hubspot.slack.client.methods.params.assistant;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.databind.PropertyNamingStrategies;
 import com.fasterxml.jackson.databind.annotation.JsonNaming;
 import com.hubspot.immutables.style.HubSpotStyle;
+import com.hubspot.immutables.validation.ImmutableConditions;
 import com.hubspot.slack.client.methods.interceptor.HasChannel;
+import java.util.List;
+import java.util.Optional;
 import org.immutables.value.Value;
 
 @Value.Immutable
 @HubSpotStyle
+@JsonInclude(JsonInclude.Include.NON_ABSENT)
 @JsonNaming(PropertyNamingStrategies.SnakeCaseStrategy.class)
 public interface SetThreadStatusParamsIF extends HasChannel {
+  int MAX_LOADING_MESSAGES = 10;
+
   @Value.Derived
   default String getChannel() {
     return getChannelId();
@@ -18,4 +25,30 @@ default String getChannel() {
   String getStatus();
 
   String getThreadTs();
+
+  @JsonInclude(JsonInclude.Include.NON_EMPTY)
+  List<String> getLoadingMessages();
+
+  Optional<String> getIconEmoji();
+
+  Optional<String> getIconUrl();
+
+  Optional<String> getUsername();
+
+  @Value.Check
+  default void checkLoadingMessagesWithinLimit() {
+    ImmutableConditions.checkValid(
+      getLoadingMessages().size() <= MAX_LOADING_MESSAGES,
+      "loadingMessages cannot contain more than %s messages",
+      MAX_LOADING_MESSAGES
+    );
+  }
+
+  @Value.Check
+  default void checkIconNotBothPresent() {
+    ImmutableConditions.checkValid(
+      !(getIconEmoji().isPresent() && getIconUrl().isPresent()),
+      "Only one of iconEmoji or iconUrl may be set"
+    );
+  }
 }
diff --git a/slack-base/src/test/java/com/hubspot/slack/client/methods/params/assistant/SetThreadStatusParamsValidationTest.java b/slack-base/src/test/java/com/hubspot/slack/client/methods/params/assistant/SetThreadStatusParamsValidationTest.java
new file mode 100644
index 00000000..305b9566
--- /dev/null
+++ b/slack-base/src/test/java/com/hubspot/slack/client/methods/params/assistant/SetThreadStatusParamsValidationTest.java
@@ -0,0 +1,102 @@
+package com.hubspot.slack.client.methods.params.assistant;
+
+import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import com.hubspot.immutables.validation.InvalidImmutableStateException;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import org.junit.Test;
+
+public class SetThreadStatusParamsValidationTest {
+
+  private static final String CHANNEL_ID = "C123";
+  private static final String THREAD_TS = "1234.5678";
+  private static final String STATUS = "is thinking...";
+
+  @Test
+  public void itBuildsWithoutLoadingMessages() {
+    assertThatCode(() ->
+        SetThreadStatusParams
+          .builder()
+          .setChannelId(CHANNEL_ID)
+          .setThreadTs(THREAD_TS)
+          .setStatus(STATUS)
+          .build()
+      )
+      .doesNotThrowAnyException();
+  }
+
+  @Test
+  public void itBuildsWithMaxLoadingMessages() {
+    assertThatCode(() ->
+        SetThreadStatusParams
+          .builder()
+          .setChannelId(CHANNEL_ID)
+          .setThreadTs(THREAD_TS)
+          .setStatus(STATUS)
+          .addAllLoadingMessages(
+            loadingMessages(SetThreadStatusParams.MAX_LOADING_MESSAGES)
+          )
+          .build()
+      )
+      .doesNotThrowAnyException();
+  }
+
+  @Test
+  public void itFailsToBuildWithTooManyLoadingMessages() {
+    assertThatThrownBy(() ->
+        SetThreadStatusParams
+          .builder()
+          .setChannelId(CHANNEL_ID)
+          .setThreadTs(THREAD_TS)
+          .setStatus(STATUS)
+          .addAllLoadingMessages(
+            loadingMessages(SetThreadStatusParams.MAX_LOADING_MESSAGES + 1)
+          )
+          .build()
+      )
+      .isInstanceOf(InvalidImmutableStateException.class)
+      .hasMessageContaining("loadingMessages");
+  }
+
+  @Test
+  public void itBuildsWithOptionalFields() {
+    assertThatCode(() ->
+        SetThreadStatusParams
+          .builder()
+          .setChannelId(CHANNEL_ID)
+          .setThreadTs(THREAD_TS)
+          .setStatus(STATUS)
+          .setIconEmoji(Optional.of(":robot_face:"))
+          .setUsername(Optional.of("My Bot"))
+          .build()
+      )
+      .doesNotThrowAnyException();
+  }
+
+  @Test
+  public void itFailsToBuildWithBothIconEmojiAndIconUrl() {
+    assertThatThrownBy(() ->
+        SetThreadStatusParams
+          .builder()
+          .setChannelId(CHANNEL_ID)
+          .setThreadTs(THREAD_TS)
+          .setStatus(STATUS)
+          .setIconEmoji(Optional.of(":robot_face:"))
+          .setIconUrl(Optional.of("https://example.com/icon.png"))
+          .build()
+      )
+      .isInstanceOf(InvalidImmutableStateException.class)
+      .hasMessageContaining("iconEmoji")
+      .hasMessageContaining("iconUrl");
+  }
+
+  private static Iterable<String> loadingMessages(int count) {
+    return IntStream
+      .range(0, count)
+      .mapToObj(i -> "message " + i)
+      .collect(Collectors.toList());
+  }
+}