LLM.swift is a simple and readable library that allows you to interact with large language models locally with ease for macOS, iOS, watchOS, tvOS, and visionOS.

What's New




  • fixed a problem caused by llama.cpp API change.

What's Changed

  • Pass false for special tokens to be compatible with llama.cpp commit 40f74e4 by @shawiz in #21

New Contributors

Full Changelog: v1.5.0...v1.5.1


LLM.swift is a simple, and readable library which lets you locally interact with LLMs with ease for macOS, iOS, visionOS, watchOS, and tvOS.


sometimes it's a good idea to tinker with maxTokenCount parameter for initialization of LLM, due to the memory and computation it needs. especially in mobile devices, if you want better speed, lower the number, but if you set it too low—to a point where two turns cannot even fit—you will experience quality decrease as context will be cut off. so adjust value according to your usecases.

Minimal Example

if you've already bundled your model:

let bot = LLM(from: Bundle.main.url(forResource: "mistral-7b-instruct-v0.2.Q4_K_M", withExtension: "gguf")!, template: .mistral)
let question = bot.preprocess("What's the meaning of life?", [])
let answer = await bot.getCompletion(from: question)

if you want to initialize with huggingface model:

let systemPrompt = "You are a sentient AI with emotions."
let bot = await LLM(from: HuggingFaceModel("TheBloke/TinyLlama-1.1B-Chat-v1.0-GGUF", .Q2_K, template: .chatML(systemPrompt)))
let question = bot.preprocess("What's the meaning of life?", [])
let answer = await bot.getCompletion(from: question)



this is a minimal SwiftUI example that i did use for testing. mistral 7B based model is working on iPad Air 5th gen(Q5_K_M) and iPhone 12 mini(Q2_K).
however, generally speaking, for mobile devices, 3B >= parameter models are recommended. check this benchmark for more details.

init with from model file that you bundled in your project

import SwiftUI
import LLM

class Bot: LLM {
    convenience init() {
        let url = Bundle.main.url(forResource: "openhermes-2.5-mistral-7b.Q4_K_M", withExtension: "gguf")!
        let systemPrompt = "You are a sentient AI with emotions."
        self.init(from: url, template: .chatML(systemPrompt))

struct BotView: View {
    @ObservedObject var bot: Bot
    @State var input = "Give me seven national flag emojis people use the most; You must include South Korea."
    init(_ bot: Bot) { self.bot = bot }
    func respond() { Task { await bot.respond(to: input) } }
    func stop() { bot.stop() }
    var body: some View {
        VStack(alignment: .leading) {
            ScrollView { Text(bot.output).monospaced() }
            HStack {
                ZStack {
                    RoundedRectangle(cornerRadius: 8).foregroundStyle(.thinMaterial).frame(height: 40)
                    TextField("input", text: $input).padding(8)
                Button(action: respond) { Image(systemName: "paperplane.fill") }
                Button(action: stop) { Image(systemName: "xmark") }
        }.frame(maxWidth: .infinity).padding()

struct ContentView: View {
    var body: some View {

init with HuggingFaceModel (gguf) directly from internet

class Bot: LLM {
    convenience init?(_ update: @escaping (Double) -> Void) async {
        let systemPrompt = "You are a sentient AI with emotions."
        let model = HuggingFaceModel("TheBloke/TinyLlama-1.1B-Chat-v1.0-GGUF", .Q2_K, template: .chatML(systemPrompt))
        try? await self.init(from: model) { progress in update(progress) }


struct ContentView: View {
    @State var bot: Bot? = nil
    @State var progress: CGFloat = 0
    func updateProgress(_ progress: Double) {
        self.progress = CGFloat(progress)
    var body: some View {
        if let bot {
        } else {
            ProgressView(value: progress) {
                Text("loading huggingface model...")
            } currentValueLabel: {
                Text(String(format: "%.2f%%", progress * 100))
            .onAppear() { Task {
                let bot = await Bot(updateProgress)
                await MainActor.run { self.bot = bot }
            } }


i intentionally used tinyLLaMA Q2_K quantization because it's useful to test due to its small size. it will most likely produce gibberish, but not heavily quantized model is pretty good. it is a very useful model, if you know where to use it.


all you have to do is to use SPM, or copy the code to your project since it's only a single file.

dependencies: [
    .package(url: "https://github.com/eastriverlee/LLM.swift/", branch: "main"),

optionally, if you care more about stability rather than benefitting from speed of llama.cpp's development cycle you can choose the pinned branch with pinned dependency.

dependencies: [
    .package(url: "https://github.com/eastriverlee/LLM.swift/", branch: "pinned"),


LLM.swift is basically a lightweight abstraction layer over llama.cpp package, so that it stays as performant as possible while is always up to date. so theoretically, any model that works on llama.cpp should work with this library as well.
It's only a single file library, so you can copy, study and modify the code however you want.

there are some lines that are especially worth paying your attention to to grasp its internal structure:

public typealias Chat = (role: Role, content: String)
public enum Role {
    case user
    case bot
public var history: [Chat]
public var preprocess: (_ input: String, _ history: [Chat]) -> String = { input, _ in return input }
public var postprocess: (_ output: String) -> Void                    = { print($0) }
public var update: (_ outputDelta: String?) -> Void                   = { _ in }

public func respond(to input: String, with makeOutputFrom: @escaping (AsyncStream<String>) async -> String) async {
    guard isAvailable else { return }
    isAvailable = false
    self.input = input
    let processedInput = preprocess(input, history)
    let response = getResponse(from: processedInput)
    let output = await makeOutputFrom(response)
    history += [(.user, input), (.bot, output)]
    if historyLimit < history.count {
    isAvailable = true

open func respond(to input: String) async {
    await respond(to: input) { [self] response in
        await setOutput(to: "")
        for await responseDelta in response {
            await setOutput(to: output + responseDelta)
        let trimmedOutput = output.trimmingCharacters(in: .whitespacesAndNewlines)
        await setOutput(to: trimmedOutput.isEmpty ? "..." : trimmedOutput)
        return output


as you can see, func respond(to input: String) async has an open access, so that you can override it when your class inherits LLM and want some fine grained control over.

there are three functions users can define when initializing LLM class:

  • var preprocess: (_ input: String, _ history: [Chat]) -> String
  • var postprocess: (_ output: String) -> Void
  • var update: (_ outputDelta: String?) -> Void they are used in respond function.


preprocess is commonly used for making the user input conform to a chat template. if you don't provide this, LLM will just work as a completion model.

for example, this is the ChatML template, that is adopted by many chat models:

SYSTEM PROMPT<|im_end|> 
USER PROMPT<|im_end|> 

to use this chat format, you should use a function that goes like this:

self.preprocess = { input, history in
    let systemPrompt = "You are a sentient AI with emotions."
    var processed = "<|im_start|>system\n\(systemPrompt)<|im_end|>\n"
    for chat in history {
        processed += "<|im_start|>\(chat.role == .user ? "user" : "assistant")\n\(chat.content)<|im_end|>\n"
    processed += "<|im_start|>user\n\(input)<|im_end|>\n"
    processed += "<|im_start|>assistant\n"
    return processed

but for convenience, you can use Template struct that is specifically made for this:

// you can use the static function that is already available for this:

self.preprocess = Template.chatML("You are a sentient AI with emotions.").preprocess

// or even better
// you can set [template] property right away, so that it handles [preprocess] and [stopSequence] both:

self.template = .chatML("You are a sentient AI with emotions.")

// which is the same thing as:

self.template = Template(
    system: ("<|im_start|>system\n", "<|im_end|>\n"),
    user: ("<|im_start|>user\n", "<|im_end|>\n"),
    bot: ("<|im_start|>assistant\n", "<|im_end|>\n"),
    stopSequence: "<|im_end|>",
    systemPrompt: "You are a sentient AI with emotions."


checking LLMTests.swift will help you understand how preprocess works better.


postprocess can be used for executing according to the output just made using user input.
the default is set to { print($0) }, so that it will print the output when it's finished generating by meeting EOS or stopSequence. this has many usages. for instance, this can be used to implement your own function calling logic.


if you use regular func respond(to input: String) async update function that you set will get called every time when you get outputDelta.
outputDelta is nil when it stops generating the output.

if you want more control over everything you can use func respond(to input: String, with makeOutputFrom: @escaping (AsyncStream<String>) async -> String) async instead, which the aforementioned function uses internally, to define your own version of makeOutputFrom function that is used to make String typed output out of AsyncStream<String> and add to its history. in this case, update function will be ignored unless you use it. check func respond(to input: String) async implementation shown above to understand how it works.


  • Swift Tools 5.9.0
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Last updated: Wed May 29 2024 12:10:16 GMT-0900 (Hawaii-Aleutian Daylight Time)