diff --git a/CHANGELOG.md b/CHANGELOG.md
index c6614ce21..17309e503 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,7 +7,7 @@
 - chore: update json-as and remove hack [#857](https://github.com/hypermodeinc/modus/pull/857)
 - chore: rename agent lifecycle methods and APIs [#858](https://github.com/hypermodeinc/modus/pull/858)
 - feat: enforce WASI reactor mode [#859](https://github.com/hypermodeinc/modus/pull/859)
-- feat: return user and chat errors in API response [#863](https://github.com/hypermodeinc/modus/pull/863)
+- feat: return user and chat errors in API response [#863](https://github.com/hypermodeinc/modus/pull/863) [#864](https://github.com/hypermodeinc/modus/pull/864)
 - feat: list agents on health endpoint [#865](https://github.com/hypermodeinc/modus/pull/865)
 - feat: add agent management APIs [#866](https://github.com/hypermodeinc/modus/pull/866)
 
diff --git a/sdk/assemblyscript/src/assembly/models.ts b/sdk/assemblyscript/src/assembly/models.ts
index f5f9b3422..104d00895 100644
--- a/sdk/assemblyscript/src/assembly/models.ts
+++ b/sdk/assemblyscript/src/assembly/models.ts
@@ -58,11 +58,18 @@ export interface ModelFactory {
   getModel<T extends Model>(modelName: string): T;
 }
 
+
+@json
+export abstract class ModelError {
+  abstract toString(): string;
+}
+
 export abstract class Model<TInput = unknown, TOutput = unknown> {
   static invoker: ModelInvoker | null = null;
   protected constructor(public info: ModelInfo) {}
 
   debug: boolean = false;
+  validator: ((data: string) => ModelError | null) | null = null;
 
   /**
    * Invokes the model with the given input.
@@ -81,7 +88,7 @@ export abstract class Model<TInput = unknown, TOutput = unknown> {
     }
 
     const outputJson = Model.invoker(modelName, inputJson);
-    if (!outputJson) {
+    if (outputJson === null) {
       throw new Error(`Failed to invoke ${modelName} model.`);
     }
 
@@ -89,6 +96,13 @@ export abstract class Model<TInput = unknown, TOutput = unknown> {
       console.debug(`Received output: ${outputJson}`);
     }
 
+    if (this.validator) {
+      const err = this.validator(outputJson);
+      if (err !== null) {
+        utils.throwUserError(`The chat model returned an error: ${err}`);
+      }
+    }
+
     return JSON.parse<TOutput>(outputJson);
   }
 }
diff --git a/sdk/assemblyscript/src/assembly/utils.ts b/sdk/assemblyscript/src/assembly/utils.ts
index 6e21dd5a9..9e81a1ff4 100644
--- a/sdk/assemblyscript/src/assembly/utils.ts
+++ b/sdk/assemblyscript/src/assembly/utils.ts
@@ -7,6 +7,19 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+/**
+ * Checks if the result is invalid, by determining if it is a null pointer.
+ * This will work for any managed type, regardless of whether it is nullable or not.
+ */
 export function resultIsInvalid<T>(result: T): bool {
   return changetype<usize>(result) == 0;
 }
+
+/**
+ * Logs an error intended for the user, and exits.
+ * The message will be displayed in the API response, and in the console logs.
+ */
+export function throwUserError(message: string): void {
+  console.error(message);
+  process.exit(1);
+}
diff --git a/sdk/assemblyscript/src/models/openai/chat.ts b/sdk/assemblyscript/src/models/openai/chat.ts
index 5c5df6697..689d85746 100644
--- a/sdk/assemblyscript/src/models/openai/chat.ts
+++ b/sdk/assemblyscript/src/models/openai/chat.ts
@@ -7,7 +7,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { Model } from "../../assembly/models";
+import { Model, ModelError } from "../../assembly/models";
 import { JSON } from "json-as";
 import * as base64 from "as-base64/assembly";
 
@@ -24,6 +24,7 @@ export class OpenAIChatModel extends Model<OpenAIChatInput, OpenAIChatOutput> {
    * @returns An input object that can be passed to the `invoke` method.
    */
   createInput(messages: RequestMessage[]): OpenAIChatInput {
+    this.validator = validateChatModelResponse;
     const model = this.info.fullName.toLowerCase();
     return <OpenAIChatInput>{ model, messages };
   }
@@ -1587,3 +1588,49 @@ export function parseMessages(data: string): RequestMessage[] {
     (msg) => new RawMessage(msg.toString()),
   );
 }
+
+// Validates the response from the chat model output.
+function validateChatModelResponse(data: string): ModelError | null {
+  if (data.length == 0) {
+    throw new Error("No response received from model invocation");
+  }
+
+  const obj = JSON.parse<JSON.Obj>(data);
+  const error = obj.get("error");
+  if (error) {
+    return JSON.parse<ChatModelError>(error.toString());
+    // return error.get<ChatModelError>(); // todo: this should work instead of the above line, but fails as of json-as v1.1.14
+  }
+
+  return null;
+}
+
+/**
+ * Represents an error returned from the OpenAI Chat API.
+ */
+@json
+class ChatModelError extends ModelError {
+  /**
+   * The error type.
+   */
+  type: string = "";
+
+  /**
+   * A human-readable description of the error.
+   */
+  message: string = "";
+
+  /**
+   * The parameter related to the error, if any.
+   */
+  param: string | null = null;
+
+  /**
+   * The error code, if any.
+   */
+  code: string | null = null;
+
+  toString(): string {
+    return this.message;
+  }
+}