diff --git a/apps/chat-e2e/src/assertions/api/apiAssertion.ts b/apps/chat-e2e/src/assertions/api/apiAssertion.ts
index b64b93150..0b5de1a92 100644
--- a/apps/chat-e2e/src/assertions/api/apiAssertion.ts
+++ b/apps/chat-e2e/src/assertions/api/apiAssertion.ts
@@ -58,7 +58,7 @@ export class ApiAssertion {
     expectedModel: DialAIEntityModel,
   ) {
     expect
-      .soft(request.modelId, ExpectedMessages.chatRequestModelIsValid)
+      .soft(request.model?.id, ExpectedMessages.chatRequestModelIsValid)
       .toBe(expectedModel.id);
   }
 
diff --git a/apps/chat-e2e/src/testData/api/chatApiHelper.ts b/apps/chat-e2e/src/testData/api/chatApiHelper.ts
index 405e66ad8..5ea414bf5 100644
--- a/apps/chat-e2e/src/testData/api/chatApiHelper.ts
+++ b/apps/chat-e2e/src/testData/api/chatApiHelper.ts
@@ -1,7 +1,7 @@
 import { Conversation } from '@/chat/types/chat';
 import { API } from '@/src/testData';
 import { BaseApiHelper } from '@/src/testData/api/baseApiHelper';
-import { BucketUtil } from '@/src/utils';
+import { BucketUtil, ModelsUtil } from '@/src/utils';
 
 export class ChatApiHelper extends BaseApiHelper {
   public buildRequestData(conversation: Conversation) {
@@ -25,7 +25,7 @@ export class ChatApiHelper extends BaseApiHelper {
     const commonData = {
       id: `conversations/${BucketUtil.getBucket()}/` + conversation.id,
       messages: [userMessage],
-      modelId: conversation.model.id,
+      model: ModelsUtil.getOpenAIEntity(conversation.model.id),
       prompt: conversation.prompt,
       temperature: conversation.temperature,
       selectedAddons: conversation.selectedAddons,
@@ -34,7 +34,9 @@ export class ChatApiHelper extends BaseApiHelper {
     return conversation.assistantModelId
       ? {
           ...commonData,
-          assistantModelId: conversation.assistantModelId,
+          assistantModel: ModelsUtil.getOpenAIEntity(
+            conversation.assistantModelId,
+          ),
         }
       : commonData;
   }
diff --git a/apps/chat-e2e/src/tests/chatHeader.test.ts b/apps/chat-e2e/src/tests/chatHeader.test.ts
index 309fb530e..464fbd8eb 100644
--- a/apps/chat-e2e/src/tests/chatHeader.test.ts
+++ b/apps/chat-e2e/src/tests/chatHeader.test.ts
@@ -66,7 +66,7 @@ dialTest(
         const requestsData = await chat.sendRequestWithKeyboard(request, false);
 
         expect
-          .soft(requestsData.modelId, ExpectedMessages.requestModeIdIsValid)
+          .soft(requestsData.model.id, ExpectedMessages.requestModeIdIsValid)
           .toBe(conversation.model.id);
         expect
           .soft(requestsData.prompt, ExpectedMessages.requestPromptIsValid)
diff --git a/apps/chat-e2e/src/tests/compareMode.test.ts b/apps/chat-e2e/src/tests/compareMode.test.ts
index 5fd6fd093..94b6e671c 100644
--- a/apps/chat-e2e/src/tests/compareMode.test.ts
+++ b/apps/chat-e2e/src/tests/compareMode.test.ts
@@ -551,7 +551,7 @@ dialTest(
 
         expect
           .soft(
-            requestsData.rightRequest.modelId,
+            requestsData.rightRequest.model.id,
             ExpectedMessages.requestModeIdIsValid,
           )
           .toBe(defaultModel.id);
@@ -570,7 +570,7 @@ dialTest(
 
         expect
           .soft(
-            requestsData.leftRequest.modelId,
+            requestsData.leftRequest.model.id,
             ExpectedMessages.requestModeIdIsValid,
           )
           .toBe(aModel.id);
@@ -1460,13 +1460,13 @@ dialTest(
         );
         expect
           .soft(
-            requestsData.rightRequest.modelId,
+            requestsData.rightRequest.model.id,
             ExpectedMessages.requestModeIdIsValid,
           )
           .toBe(firstFolderConversation.conversations[0].model.id);
         expect
           .soft(
-            requestsData.leftRequest.modelId,
+            requestsData.leftRequest.model.id,
             ExpectedMessages.requestModeIdIsValid,
           )
           .toBe(secondFolderConversation.conversations[0].model.id);
diff --git a/apps/chat-e2e/src/tests/replay.test.ts b/apps/chat-e2e/src/tests/replay.test.ts
index 5b4e526f9..eb113eacd 100644
--- a/apps/chat-e2e/src/tests/replay.test.ts
+++ b/apps/chat-e2e/src/tests/replay.test.ts
@@ -308,7 +308,10 @@ dialTest(
       'Verify chat API request is sent with correct settings',
       async () => {
         expect
-          .soft(replayRequest.modelId, ExpectedMessages.chatRequestModelIsValid)
+          .soft(
+            replayRequest.model?.id,
+            ExpectedMessages.chatRequestModelIsValid,
+          )
           .toBe(replayModel.id);
         expect
           .soft(replayRequest.prompt, ExpectedMessages.chatRequestPromptIsValid)
@@ -413,7 +416,10 @@ dialTest(
           conversation.messages[0].content,
         );
         expect
-          .soft(replayRequest.modelId, ExpectedMessages.chatRequestModelIsValid)
+          .soft(
+            replayRequest.model?.id,
+            ExpectedMessages.chatRequestModelIsValid,
+          )
           .toBe(conversation.model.id);
         expect
           .soft(replayRequest.prompt, ExpectedMessages.chatRequestPromptIsValid)
@@ -651,7 +657,10 @@ dialTest(
           true,
         );
         expect
-          .soft(replayRequest.modelId, ExpectedMessages.chatRequestModelIsValid)
+          .soft(
+            replayRequest.model.id,
+            ExpectedMessages.chatRequestModelIsValid,
+          )
           .toBe(conversation.model.id);
       },
     );
@@ -674,7 +683,7 @@ dialTest(
         const newMessage = '2+3';
         const newRequest = await chat.sendRequestWithButton(newMessage);
         expect
-          .soft(newRequest.modelId, ExpectedMessages.chatRequestModelIsValid)
+          .soft(newRequest.model.id, ExpectedMessages.chatRequestModelIsValid)
           .toBe(conversation.model.id);
         expect
           .soft(
@@ -850,7 +859,10 @@ dialTest(
           const modelId =
             i === 1 ? ImportedModelIds.CHAT_BISON : ImportedModelIds.GPT_4;
           expect
-            .soft(requests[i].modelId, ExpectedMessages.chatRequestModelIsValid)
+            .soft(
+              requests[i].model.id,
+              ExpectedMessages.chatRequestModelIsValid,
+            )
             .toBe(modelId);
         }
       },
diff --git a/apps/chat/src/components/Chat/Chat.tsx b/apps/chat/src/components/Chat/Chat.tsx
index eaa26ac31..fdc713702 100644
--- a/apps/chat/src/components/Chat/Chat.tsx
+++ b/apps/chat/src/components/Chat/Chat.tsx
@@ -310,14 +310,16 @@ export const ChatView = memo(() => {
   useLayoutEffect(() => {
     if (selectedConversations.length > 0) {
       const mergedMessages: MergedMessages[] = [];
-      const firstConversationMessages = excludeSystemMessages(
-        selectedConversations[0].messages,
+      const userMessages = selectedConversations.map((conv) =>
+        excludeSystemMessages(conv.messages),
       );
-      for (let i = 0; i < firstConversationMessages.length; i++) {
+      const messagesLength = userMessages[0].length;
+
+      for (let i = 0; i < messagesLength; i++) {
         mergedMessages.push(
-          selectedConversations.map((conv) => [
+          selectedConversations.map((conv, convIndex) => [
             conv,
-            excludeSystemMessages(conv.messages)[i] || {
+            userMessages[convIndex][i] || {
               role: Role.Assistant,
               content: '',
             },
diff --git a/apps/chat/src/pages/api/chat.ts b/apps/chat/src/pages/api/chat.ts
index b7551d777..3ea7cfb8f 100644
--- a/apps/chat/src/pages/api/chat.ts
+++ b/apps/chat/src/pages/api/chat.ts
@@ -9,7 +9,6 @@ import {
   getUserMessageCustomContent,
   limitMessagesByTokens,
 } from '@/src/utils/server/chat';
-import { getSortedEntities } from '@/src/utils/server/get-sorted-entities';
 
 import { ChatBody } from '@/src/types/chat';
 import { EntityType } from '@/src/types/common';
@@ -30,33 +29,22 @@ const handler = async (req: NextApiRequest, res: NextApiResponse) => {
   }
 
   const {
-    modelId,
     id,
     messages,
     prompt,
     temperature,
     selectedAddons,
-    assistantModelId,
+    model,
+    assistantModel,
   } = req.body as ChatBody;
 
   try {
     const token = await getToken({ req });
-    const models = await getSortedEntities(token);
-    const model = models.find(
-      ({ id, reference }) => id === modelId || reference === modelId,
-    );
-    const assistantModel = assistantModelId
-      ? models.find(
-          ({ id, reference }) =>
-            id === assistantModelId || reference === assistantModelId,
-        )
-      : undefined;
 
     if (
       !id ||
       !model ||
-      (!!assistantModelId && !assistantModel) ||
-      (!!assistantModelId && model.type !== EntityType.Assistant) ||
+      (!!assistantModel && model.type !== EntityType.Assistant) ||
       (!prompt && !messages?.length)
     ) {
       return res.status(400).send(errorsMessages[400]);
@@ -119,7 +107,7 @@ const handler = async (req: NextApiRequest, res: NextApiResponse) => {
       temperature: temperatureToUse,
       messages: messagesToSend,
       selectedAddonsIds: selectedAddons?.length ? selectedAddons : undefined,
-      assistantModelId,
+      assistantModelId: assistantModel?.id,
       userJWT: token?.access_token as string,
       chatId: id,
       jobTitle: token?.jobTitle as string,
@@ -158,7 +146,7 @@ const handler = async (req: NextApiRequest, res: NextApiResponse) => {
     return chatErrorHandler({
       error,
       res,
-      msg: `Error while sending chat request to '${modelId}'`,
+      msg: `Error while sending chat request to '${model?.id}'`,
     });
   }
 };
diff --git a/apps/chat/src/store/conversations/conversations.epics.ts b/apps/chat/src/store/conversations/conversations.epics.ts
index 894cea560..be929b1ef 100644
--- a/apps/chat/src/store/conversations/conversations.epics.ts
+++ b/apps/chat/src/store/conversations/conversations.epics.ts
@@ -1333,14 +1333,14 @@ const streamMessageEpic: AppEpic = (action$, state$) =>
       }
       if (conversationModelType === EntityType.Assistant && assistantModelId) {
         modelAdditionalSettings = {
-          assistantModelId,
+          assistantModel: modelsMap[assistantModelId],
           temperature: payload.conversation.temperature,
           selectedAddons,
         };
       }
 
       const chatBody: ChatBody = {
-        modelId: payload.conversation.model.id,
+        model: modelsMap[payload.conversation.model.id],
         messages: payload.conversation.messages
           .filter(
             (message, index) =>
diff --git a/apps/chat/src/types/chat.ts b/apps/chat/src/types/chat.ts
index f9f28723e..08bc79ee4 100644
--- a/apps/chat/src/types/chat.ts
+++ b/apps/chat/src/types/chat.ts
@@ -1,3 +1,5 @@
+import { DialAIEntityModel } from '@/src/types/models';
+
 import { ConversationInfo, Message, ShareEntity } from '@epam/ai-dial-shared';
 
 export enum CopyTableType {
@@ -7,13 +9,13 @@ export enum CopyTableType {
 }
 
 export interface ChatBody {
-  modelId: string;
   messages: Message[];
   id: string;
   prompt?: string;
   temperature?: number;
   selectedAddons?: string[];
-  assistantModelId?: string;
+  model?: DialAIEntityModel;
+  assistantModel?: DialAIEntityModel;
 }
 
 export interface RateBody {