diff --git a/src/custom-llm.ts b/src/custom-llm.ts
new file mode 100644
index 0000000..6266fc9
--- /dev/null
+++ b/src/custom-llm.ts
@@ -0,0 +1,116 @@
+/* eslint-disable @typescript-eslint/no-magic-numbers */
+import { LLM, type BaseLLMParams } from "@langchain/core/language_models/llms";
+import { type CallbackManagerForLLMRun } from "@langchain/core/callbacks/manager";
+import { GenerationChunk } from "@langchain/core/outputs";
+import { type OpenAIClient } from "@langchain/openai";
+
+// eslint-disable-next-line @typescript-eslint/consistent-type-definitions
+export interface UpstashLLMParameters extends BaseLLMParams {
+  /** Writer API key */
+  apiKey?: string;
+
+  /** Model to use */
+  model?: string;
+
+  /** Sampling temperature to use */
+  temperature?: number;
+
+  /** Minimum number of tokens to generate. */
+  minTokens?: number;
+
+  /** Maximum number of tokens to generate in the completion. */
+  maxTokens?: number;
+
+  /** Generates this many completions server-side and returns the "best"." */
+  bestOf?: number;
+
+  /** Penalizes repeated tokens according to frequency. */
+  frequencyPenalty?: number;
+
+  /** Penalizes repeated tokens regardless of frequency. */
+  presencePenalty?: number;
+
+  /** Total probability mass of tokens to consider at each step. */
+  topP?: number;
+}
+
+export default class UpstashLLM extends LLM {
+  temperature = 0.7;
+
+  maxTokens = 256;
+
+  topP = 1;
+
+  frequencyPenalty = 0;
+
+  presencePenalty = 0;
+
+  n = 1;
+
+  model = "mistralai/Mistral-7B-Instruct-v0.2";
+
+  batchSize = 20;
+
+  apiKey: string;
+
+  constructor(fields: UpstashLLMParameters) {
+    super({});
+    if (!fields.apiKey) {
+      throw new Error("apiKey is required");
+    }
+
+    this.topP = fields.topP ?? this.topP;
+    this.temperature = fields.temperature ?? this.temperature;
+    this.maxTokens = fields.maxTokens ?? this.maxTokens;
+    this.frequencyPenalty = fields.frequencyPenalty ?? this.frequencyPenalty;
+    this.presencePenalty = fields.presencePenalty ?? this.presencePenalty;
+    this.model = fields.model ?? this.model;
+    this.apiKey = fields.apiKey;
+  }
+
+  _llmType() {
+    return "Upstash LLM";
+  }
+
+  async _call(prompt: string) {
+    const url = `${process.env.UPSTASH_MODELS_BACKEND_URL}/v1/completions`;
+    const data = {
+      prompt: prompt,
+      model: this.model,
+      max_tokens: this.maxTokens,
+      top_p: this.topP,
+      temperature: this.temperature,
+      frequency_penalty: this.frequencyPenalty,
+    };
+
+    const response = await fetch(url, {
+      method: "POST",
+      body: JSON.stringify(data),
+      headers: {
+        Authorization: `Bearer ${this.apiKey}`,
+        Accept: "application/json",
+        "Content-Type": "application/json",
+      },
+    });
+
+    const object = await response.json();
+
+    const result = object as OpenAIClient.Completions.Completion;
+
+    return result.choices[0].text;
+  }
+
+  async *_streamResponseChunks(
+    prompt: string,
+    options: this["ParsedCallOptions"],
+    runManager?: CallbackManagerForLLMRun
+  ): AsyncGenerator<GenerationChunk> {
+    for (const letter of prompt.slice(0, this.n)) {
+      yield new GenerationChunk({
+        text: letter,
+      });
+
+      await runManager?.handleLLMNewToken(letter);
+    }
+  }
+}
diff --git a/src/rag-chat.test.ts b/src/rag-chat.test.ts
index e23cb3e..85b1c96 100644
--- a/src/rag-chat.test.ts
+++ b/src/rag-chat.test.ts
@@ -10,12 +10,14 @@ import { DEFAULT_REDIS_DB_NAME, DEFAULT_VECTOR_DB_NAME } from "./constants";
 import { RatelimitUpstashError } from "./error";
 import { PromptTemplate } from "@langchain/core/prompts";
 import { sleep } from "bun";
+import UpstashLLM from "./custom-llm";
 
 describe("RAG Chat with advance configs and direct instances", async () => {
   const vector = new Index({
     token: process.env.UPSTASH_VECTOR_REST_TOKEN!,
     url: process.env.UPSTASH_VECTOR_REST_URL!,
   });
+
   const ragChat = await RAGChat.initialize({
     email: process.env.UPSTASH_EMAIL!,
     token: process.env.UPSTASH_TOKEN!,
@@ -49,6 +51,7 @@ describe("RAG Chat with advance configs and direct instances", async () => {
       "What year was the construction of the Eiffel Tower completed, and what is its height?",
       { stream: false }
     )) as AIMessage;
+
     expect(result.content).toContain("330");
   });
 
@@ -56,6 +59,7 @@ describe("RAG Chat with advance configs and direct instances", async () => {
     const result = (await ragChat.chat("Which famous artworks can be found in the Louvre Museum?", {
       stream: true,
     })) as StreamingTextResponse;
+
     expect(result).toBeTruthy();
   });
 });
@@ -252,3 +256,44 @@ describe("RAG Chat with custom template", async () => {
     { timeout: 30_000 }
   );
 });
+
+describe("RAG Chat with custom LLM", async () => {
+  const ragChat = await RAGChat.initialize({
+    email: process.env.UPSTASH_EMAIL!,
+    token: process.env.UPSTASH_TOKEN!,
+    model: new UpstashLLM({
+      apiKey: process.env.UPSTASH_MODELS_REST_TOKEN,
+      model: "mistralai/Mistral-7B-Instruct-v0.2",
+    }),
+    redis: new Redis({
+      token: process.env.UPSTASH_REDIS_REST_TOKEN!,
+      url: process.env.UPSTASH_REDIS_REST_URL!,
+    }),
+  });
+
+  beforeAll(async () => {
+    await ragChat.addContext(
+      "Paris, the capital of France, is renowned for its iconic landmark, the Eiffel Tower, which was completed in 1889 and stands at 330 meters tall.",
+      "text"
+    );
+    //eslint-disable-next-line @typescript-eslint/no-magic-numbers
+    await sleep(3000);
+  });
+
+  test("should get result without streaming", async () => {
+    const result = (await ragChat.chat(
+      "What year was the construction of the Eiffel Tower completed, and what is its height?",
+      { stream: false }
+    )) as AIMessage;
+
+    expect(result).toContain("330");
+  });
+
+  test("should get result with streaming", async () => {
+    const result = (await ragChat.chat("Which famous artworks can be found in the Louvre Museum?", {
+      stream: true,
+    })) as StreamingTextResponse;
+
+    expect(result).toBeTruthy();
+  });
+});