diff --git a/package-lock.json b/package-lock.json
index e88af96e..8d062f43 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -3914,14 +3914,10 @@
       "license": "MIT"
     },
     "node_modules/decoders": {
-      "version": "1.15.0",
-      "resolved": "https://registry.npmjs.org/decoders/-/decoders-1.15.0.tgz",
-      "integrity": "sha512-KiOex7H31P2LjQgH3azmcRThaIcVGspaHIQlx6e/ik1PNUCs68QTTV8Qs6kowXCtCl4Q5yc1eGo7cbSwTqa9QA==",
-      "license": "MIT",
-      "dependencies": {
-        "debrief": "^1.2.6",
-        "lemons": "^1.4.0"
-      }
+      "version": "2.8.0",
+      "resolved": "https://registry.npmjs.org/decoders/-/decoders-2.8.0.tgz",
+      "integrity": "sha512-VONc1zao3a/RcJLaOJSpekRku/e1a3ZDVxGj7TLYUGe0ASSFTSYXgL4Uf0mYIaQarLCxSb8TlUXcC1jBLYwVOA==",
+      "license": "MIT"
     },
     "node_modules/dedent": {
       "version": "0.7.0",
@@ -10272,7 +10268,7 @@
       "version": "6.5.0",
       "license": "MIT",
       "dependencies": {
-        "decoders": "1.15.0"
+        "decoders": "^2.8.0"
       },
       "devDependencies": {
         "@rollup/plugin-commonjs": "^26.0.3",
diff --git a/packages/iframe-coordinator/package.json b/packages/iframe-coordinator/package.json
index 98bc176a..b5c63474 100644
--- a/packages/iframe-coordinator/package.json
+++ b/packages/iframe-coordinator/package.json
@@ -3,7 +3,7 @@
   "version": "6.5.0",
   "description": "Tools for coordinating embedded apps via iframes.",
   "dependencies": {
-    "decoders": "1.15.0"
+    "decoders": "^2.8.0"
   },
   "type": "module",
   "files": [
diff --git a/packages/iframe-coordinator/src/messages/ClientToHost.ts b/packages/iframe-coordinator/src/messages/ClientToHost.ts
index 59d20807..ddd2051f 100644
--- a/packages/iframe-coordinator/src/messages/ClientToHost.ts
+++ b/packages/iframe-coordinator/src/messages/ClientToHost.ts
@@ -1,4 +1,4 @@
-import { dispatch, guard } from "decoders";
+import { taggedUnion } from "decoders";
 import { decoder as clickDecoder, LabeledClick } from "./Click";
 import { decoder as keyDownDecoder, LabeledKeyDown } from "./KeyDown";
 import { LabeledStarted, startedDecoder } from "./Lifecycle";
@@ -36,18 +36,16 @@ export type ClientToHost =
  * @param msg The message requiring validation.
  */
 export function validate(msg: any): ClientToHost {
-  return guard(
-    dispatch("msgType", {
-      publish: publicationDecoder,
-      registeredKeyFired: keyDownDecoder,
-      client_started: startedDecoder,
-      clickFired: clickDecoder,
-      navRequest: navRequestDecoder,
-      notifyRequest: notifyDecoder,
-      toastRequest: notifyDecoder,
-      modalRequest: modalDecoder,
-      pageMetadata: pageMetadataDecoder,
-      promptOnLeave: promptDecoder,
-    }),
-  )(msg);
+  return taggedUnion("msgType", {
+    publish: publicationDecoder,
+    registeredKeyFired: keyDownDecoder,
+    client_started: startedDecoder,
+    clickFired: clickDecoder,
+    navRequest: navRequestDecoder,
+    notifyRequest: notifyDecoder,
+    toastRequest: notifyDecoder,
+    modalRequest: modalDecoder,
+    pageMetadata: pageMetadataDecoder,
+    promptOnLeave: promptDecoder,
+  }).verify(msg);
 }
diff --git a/packages/iframe-coordinator/src/messages/HostToClient.ts b/packages/iframe-coordinator/src/messages/HostToClient.ts
index 43c9ac13..069685f8 100644
--- a/packages/iframe-coordinator/src/messages/HostToClient.ts
+++ b/packages/iframe-coordinator/src/messages/HostToClient.ts
@@ -1,4 +1,4 @@
-import { dispatch, guard } from "decoders";
+import { taggedUnion } from "decoders";
 import { envDecoder, LabeledEnvInit } from "./Lifecycle";
 import {
   decoder as publicationDecoder,
@@ -17,7 +17,8 @@ export type HostToClient = LabeledPublication | LabeledEnvInit;
  * @param msg The message requiring validation.
  */
 export function validate(msg: any): HostToClient {
-  return guard(
-    dispatch("msgType", { publish: publicationDecoder, env_init: envDecoder }),
-  )(msg);
+  return taggedUnion("msgType", {
+    publish: publicationDecoder,
+    env_init: envDecoder,
+  }).verify(msg);
 }
diff --git a/packages/iframe-coordinator/src/messages/LabeledMsg.ts b/packages/iframe-coordinator/src/messages/LabeledMsg.ts
index ff8783d9..4b2beb55 100644
--- a/packages/iframe-coordinator/src/messages/LabeledMsg.ts
+++ b/packages/iframe-coordinator/src/messages/LabeledMsg.ts
@@ -1,13 +1,4 @@
-import {
-  constant,
-  Decoder,
-  either,
-  hardcoded,
-  map,
-  object,
-  optional,
-  string,
-} from "decoders";
+import { constant, Decoder, either, exact, optional, string } from "decoders";
 
 // This is replaced by rollup-plugin-replace with the actual version from package.json
 const version = "__PACKAGE_VERSION__";
@@ -87,20 +78,21 @@ export function labeledDecoder<T, V>(
   typeDecoder: Decoder<T>,
   msgDecoder: Decoder<V>,
 ): Decoder<LabeledMsg<T, V>> {
-  return object({
+  return exact({
     // TODO: in 4.0.0 make protocol and version fields mandatory
-    protocol: either(
-      constant<"iframe-coordinator">(API_PROTOCOL),
-      hardcoded<"iframe-coordinator">(API_PROTOCOL),
-    ),
-    version: either(string, hardcoded("unknown")),
+    protocol: optional(constant<"iframe-coordinator">(API_PROTOCOL)),
+    version: optional(string),
     msgType: typeDecoder,
     msg: msgDecoder,
     direction: optional(directionDecoder),
-  });
+  }).transform((decoded) => ({
+    ...decoded,
+    protocol: decoded.protocol ?? API_PROTOCOL,
+    version: decoded.version ?? "unknown",
+  })) as Decoder<LabeledMsg<T, V>>;
 }
 
-const directionDecoder: Decoder<MessageDirection, unknown> = either(
+const directionDecoder: Decoder<MessageDirection> = either(
   constant("ClientToHost"),
   constant("HostToClient"),
 );
diff --git a/packages/iframe-coordinator/src/messages/Lifecycle.ts b/packages/iframe-coordinator/src/messages/Lifecycle.ts
index 05eddb4c..1e31716c 100644
--- a/packages/iframe-coordinator/src/messages/Lifecycle.ts
+++ b/packages/iframe-coordinator/src/messages/Lifecycle.ts
@@ -3,10 +3,10 @@ import {
   boolean,
   constant,
   Decoder,
-  mixed,
-  object,
+  exact,
   optional,
   string,
+  unknown,
 } from "decoders";
 import { applyClientProtocol, labeledDecoder, LabeledMsg } from "./LabeledMsg";
 
@@ -23,7 +23,7 @@ export interface LabeledStarted extends LabeledMsg<"client_started", any> {
 // We don't care what is in msg for Started messages.
 const startedDecoder: Decoder<LabeledStarted> = labeledDecoder(
   constant<"client_started">("client_started"),
-  mixed,
+  unknown,
 );
 
 /**
@@ -78,13 +78,13 @@ export interface LabeledEnvInit extends LabeledMsg<"env_init", SetupData> {
 
 const envDecoder: Decoder<LabeledEnvInit> = labeledDecoder(
   constant<"env_init">("env_init"),
-  object({
+  exact({
     locale: string,
     hostRootUrl: string,
     assignedRoute: string,
     registeredKeys: optional(
       array(
-        object({
+        exact({
           key: string,
           altKey: optional(boolean),
           ctrlKey: optional(boolean),
@@ -93,7 +93,7 @@ const envDecoder: Decoder<LabeledEnvInit> = labeledDecoder(
         }),
       ),
     ),
-    custom: mixed,
+    custom: unknown,
   }),
 );
 
diff --git a/packages/iframe-coordinator/src/messages/ModalRequest.ts b/packages/iframe-coordinator/src/messages/ModalRequest.ts
index e9c3b7ff..f51fa8c4 100644
--- a/packages/iframe-coordinator/src/messages/ModalRequest.ts
+++ b/packages/iframe-coordinator/src/messages/ModalRequest.ts
@@ -1,4 +1,4 @@
-import { constant, Decoder, mixed, object, string } from "decoders";
+import { constant, Decoder, exact, string, unknown } from "decoders";
 import { labeledDecoder, LabeledMsg } from "./LabeledMsg";
 
 /**
@@ -9,7 +9,7 @@ export interface ModalRequest {
   modalId: string;
 
   /** Any data that the client wishes to send to the modal */
-  modalData: any;
+  modalData?: any;
 }
 
 /**
@@ -28,9 +28,9 @@ export interface LabeledModalRequest extends LabeledMsg<
 
 const decoder: Decoder<LabeledModalRequest> = labeledDecoder(
   constant<"modalRequest">("modalRequest"),
-  object({
+  exact({
     modalId: string,
-    modalData: mixed,
+    modalData: unknown,
   }),
 );
 
diff --git a/packages/iframe-coordinator/src/messages/Notification.ts b/packages/iframe-coordinator/src/messages/Notification.ts
index 3e87c041..ffc053ef 100644
--- a/packages/iframe-coordinator/src/messages/Notification.ts
+++ b/packages/iframe-coordinator/src/messages/Notification.ts
@@ -2,11 +2,10 @@ import {
   constant,
   Decoder,
   either,
-  map,
-  mixed,
-  object,
+  exact,
   optional,
   string,
+  unknown,
 } from "decoders";
 import { labeledDecoder, LabeledMsg } from "./LabeledMsg";
 
@@ -20,7 +19,7 @@ export interface Notification {
   /** The notification message */
   message: string;
   /** Additional host-specific options such as severity */
-  custom: any;
+  custom?: any;
 }
 
 /**
@@ -40,21 +39,19 @@ export interface LabeledNotification extends LabeledMsg<
 /**
  * Helper function to convert old message types to the new type
  */
-function alwaysMsgType(msgType: "string"): "notifyRequest" {
+function alwaysMsgType(msgType: "toastRequest"): "notifyRequest" {
   return "notifyRequest";
 }
 
-const toastTypeDecoder: Decoder<"notifyRequest"> = map(
-  constant<"toastRequest">("toastRequest"),
-  alwaysMsgType,
-);
+const toastTypeDecoder: Decoder<"notifyRequest"> =
+  constant<"toastRequest">("toastRequest").transform(alwaysMsgType);
 
 const decoder: Decoder<LabeledNotification> = labeledDecoder(
   either(constant<"notifyRequest">("notifyRequest"), toastTypeDecoder),
-  object({
+  exact({
     title: optional(string),
     message: string,
-    custom: mixed,
+    custom: unknown,
   }),
 );
 
diff --git a/packages/iframe-coordinator/src/messages/PageMetadata.ts b/packages/iframe-coordinator/src/messages/PageMetadata.ts
index a149b263..5271f5a2 100644
--- a/packages/iframe-coordinator/src/messages/PageMetadata.ts
+++ b/packages/iframe-coordinator/src/messages/PageMetadata.ts
@@ -2,10 +2,10 @@ import {
   array,
   constant,
   Decoder,
-  mixed,
-  object,
+  exact,
   optional,
   string,
+  unknown,
 } from "decoders";
 import { labeledDecoder, LabeledMsg } from "./LabeledMsg";
 
@@ -47,15 +47,15 @@ export interface LabeledPageMetadata extends LabeledMsg<
 
 const decoder: Decoder<LabeledPageMetadata> = labeledDecoder(
   constant<"pageMetadata">("pageMetadata"),
-  object({
+  exact({
     title: string,
     breadcrumbs: array(
-      object({
+      exact({
         text: string,
         href: string,
       }),
     ),
-    custom: optional(mixed),
+    custom: optional(unknown),
   }),
 );
 
diff --git a/packages/iframe-coordinator/src/messages/Publication.ts b/packages/iframe-coordinator/src/messages/Publication.ts
index 5acc6301..eff0026c 100644
--- a/packages/iframe-coordinator/src/messages/Publication.ts
+++ b/packages/iframe-coordinator/src/messages/Publication.ts
@@ -1,12 +1,4 @@
-import {
-  constant,
-  Decoder,
-  map,
-  mixed,
-  object,
-  optional,
-  string,
-} from "decoders";
+import { constant, Decoder, exact, optional, string, unknown } from "decoders";
 import { labeledDecoder, LabeledMsg } from "./LabeledMsg";
 
 /**
@@ -19,7 +11,7 @@ export interface Publication {
    */
   topic: string;
   /** Data to publish */
-  payload: any;
+  payload?: any;
   /**
    * Client the message originates from. This should not be provided when
    * calling client methods. The value will be ignored and the library
@@ -41,9 +33,9 @@ export interface LabeledPublication extends LabeledMsg<"publish", Publication> {
 
 const decoder: Decoder<LabeledPublication> = labeledDecoder(
   constant<"publish">("publish"),
-  object({
+  exact({
     topic: string,
-    payload: mixed,
+    payload: unknown,
     clientId: optional(string),
   }),
 );