Enterprise AI Governance

Custom & Private Models

Custom & Private Models

Deploy the right model for the job.

Standard hosted models do not fit every product or data environment. We deploy private, self-hosted, and on-device models where teams need tighter control, offline use, or models adapted to product-specific data and workflows.

Plan my model strategy
Explore services
Custom & Private Models

Why deploy with Callstack

Run the right model under control.

We evaluate where hosted models fall short, then deploy private, self-hosted, on-device, regional, or hosted models around your data, latency, security, and workload needs.

Keep sensitive data off third-party systems.

Self-hosted and on-device models reduce external data exposure.

Get better output from the model.

Fine-tuned or specialized models perform better on your codebase, domain, and tasks.

Choose where the model runs.

Use self-hosted, on-device, regional, or hosted models based on your security, latency, and workload needs.

Services

Choose where and how models run.

Use Cases

On-Premise LLM Deployment

Stand up self-hosted models so sensitive code and data never leave your infrastructure.

On-Device AI

Run models directly on user devices for privacy, offline use, and low-latency experiences without a cloud round-trip.

LLM Fine-Tuning

Fine-tune models on your codebase, conventions, and domain so outputs match how your teams actually build.

Model Evaluation

Benchmark candidate models against your real engineering tasks to pick the right one and prove it works.

Custom & Private Models

Start with a model evaluation.

Tell us where hosted models fall short for your team today. We'll come back with the right approach for your data and workload, and what the rollout path looks like.

Plan my model strategy

Assess → Deploy → Operate

Deploy models where the workload fits.

Assess

We assess models, controls, and exposure. Leadership gets a clear approval path.

Code and data stay in your environment
Find the gaps before rollout
1-2 WEEKS

Deploy

We deploy models, workflows, and guardrails. AI runs under the controls it needs.

Models and controls go live
Runbooks, matrices, traceability included
1-2 MONTHS

Operate

We keep the setup ready for the next review cycle. Models, policies, and controls stay up to date.

Update models, policies, and controls
Stay ready when reviews return
PER REVIEW CYCLE

Manifesto

When the way software is built changes, 
we help companies adopt it.

AI-native teams run on a system, not only on tools. Agents move the work forward. Experts make the calls that shape the outcome.

Learn Callstack Delivery Model

Case studies

What shipping at AI speed looks like

No items found.

10 years of React Native → Now in your AI stack

Start with a model evaluation.

Tell us where hosted models fall short for your team today. We'll come back with the right approach for your data and workload, and what the rollout path looks like.

Plan my model strategy

Why teams bet on Callstack

From billion-user apps to React Native core, this is why teams choose Callstack when they need to move fast and get it right.

Rocket ascending into a blue night sky with digital binary code forming its smoke trail.

10 years in React Native. Now shaping agentic engineering.

For a decade, we have helped define how teams ship with React Native. Now we are helping shape how they work with agents.

Founded in 2016 ·Backed by Viking Global Investors

React Foundation members. Core Contributors.

We are founding members of React Foundation and Core Contributors to React Native. You get direct access to people close to the decisions shaping the frameworks you use.

Open source since 2016. Our code runs in your app.

We contribute to React Native and maintain libraries across its ecosystem. Our code runs in apps used by millions of people every day.

Open Source Projects

39M+

Downloads / month

67K+

GitHub stars

300+

React Native commits

100+ Enterprise clients with 7B+ users.

We work with teams shipping at real scale. You get a partner used to high-stakes products, not learning on your roadmap.

Agent Conf. The conference for the Agentic era.

The conference we built for the shift from writing code to orchestrating agents.

Agent Conf
Gradient background blending white, light blue, and purple shades with smooth transitions.Man wearing glasses and a Stanford sweatshirt speaking into a microphone during a presentation.

We are Codex Ambassadors.

We run meetups, workshops, and hands-on 
sessions that help teams learn Codex 
and apply it in real work.

Check Events
Rocket ascending into a blue night sky with digital binary code forming its smoke trail.

10 years in React Native. Now shaping agentic engineering.

For a decade, we have helped define how teams ship with React Native. Now we are helping shape how they work with agents.

Founded in 2016 ·Backed by Viking Global Investors

React Foundation members. Core Contributors.

We are founding members of React Foundation and Core Contributors to React Native. You get direct access to people close to the decisions shaping the frameworks you use.

Open source since 2016. Our code runs in your app.

We contribute to React Native and maintain libraries across its ecosystem. Our code runs in apps used by millions of people every day.

Open Source Projects

39M+

Downloads / month

67K+

GitHub stars

300+

React Native commits

100+ Enterprise clients with 7B+ users.

We work with teams shipping at real scale. You get a partner used to high-stakes products, not learning on your roadmap.

Agent Conf. The conference for the Agentic era.

The conference we built for the shift from writing code to orchestrating agents.

Agent Conf
Gradient background blending white, light blue, and purple shades with smooth transitions.Man wearing glasses and a Stanford sweatshirt speaking into a microphone during a presentation.

We are Codex Ambassadors.

We run meetups, workshops, and hands-on 
sessions that help teams learn Codex 
and apply it in real work.

Check Events

Open Source

Want to build it on your own?

We open-source the tools behind our delivery model.
Use them, fork them, or let us run them for you.

Check All Tools
Explore AI Infrastructure
React Native AI

On-device LLM execution in React Native with Vercel AI SDK compatibility

22123
downloads / month
React Native Evals

A benchmark suite for evaluating how coding models solve real React Native tasks

91
stars
Skill Gym

Prove your agent skills work before you ship them

1500
downloads / month

Insights

Worth your time, by engineers.

Explore Insights
cover
Jun 8
·
Article

On-device AI After WWDC 2026: What's New?

Apple's 2026 AI updates move Apple Intelligence beyond a narrow text model. Foundation Models gets image input and server-backed calls, high-end devices get a stronger on-device model, and Core AI gives custom local models a native path. We're mapping these APIs into the React Native AI stack and working with early users on real app workflows.
cover
Jun 5
·
Article

Optimizing Self-Hosted Gemma for Production Inference

We optimized self-hosted Gemma 4 31B for Apex by tuning vLLM server configuration, GPU memory use, KV cache capacity, context length, multimodal limits, tensor parallelism, and MTP speculative decoding. The article covers what changed, the performance gains we measured, the latency tradeoffs, and the production setup we recommend for faster Gemma serving.
cover
May 27
·
Article

Introducing Apex: A Fast, Specialized Model for React Native

Today, we are introducing Apex, our first domain-specific coding model designed for React Native. Built on Gemma 4, Apex achieves frontier-level performance at a fraction of the cost of generalized models. It is optimized for the fast, agentic workflows our teams run daily, delivering up-to-date results with fewer tool calls.
cover
Apr 27
·
Article

When to Use Apple Foundation Models on Mobile

Apple Foundation Models are most useful on mobile when the task is small, fast, local, and not worth a cloud round trip. The real value is not replacing cloud models entirely, but using on-device AI where latency, privacy, and frequency matter most.
cover
Mar 27
·
Article

RAG Is Dead. Long Live Context Engineering for LLM Systems

Not every LLM system needs a full RAG stack. This article shows when structured context injection can replace retrieval pipelines, reducing complexity, latency, and operational overhead.
cover
Mar 18
·
Article

A Practical Guide to LLM Model Naming Conventions

The same LLM can appear in many variants because different hardware environments require different numerical precision. This article breaks down quantization, explains model naming conventions, and shows how deployment constraints shape model formats. Explore how quantization impacts performance and infrastructure costs.
cover
Mar 5
·
Article

Announcing React Native Evals

React Native Evals is a new open-source benchmark from Callstack that evaluates how coding models implement real React Native tasks. The suite ships with 39 evals across animation, async state, and navigation categories, covering libraries like Reanimated, TanStack Query, Zustand, and React Navigation.
cover
Dec 16
·
Article

Profiling MLC-LLM’s OpenCL Backend on Android: Performance Insights

MLC-LLM can run LLMs fast on-device, but we hit a nasty Android issue: the first inference froze the system UI for up to 50 seconds, then everything was fine. This post walks through how we added Perfetto-compatible traces in MLC-LLM and kernel profiling in TVM/OpenCL, and why switching from _1 to _0 model formats fixed it on Adreno.
cover
Aug 21
·
Article

On-Device Text To Speech on Apple Devices with AI SDK

We’ve added on-device speech synthesis to our Apple provider for the AI SDK, completing the feature set alongside generation, embeddings, and transcription. This integration with AVSpeechSynthesizer brings fast, private, and offline text-to-speech to React Native, with support for multiple voices, languages, and even Personal Voice on iOS 17+.
cover
Aug 6
·
Article

On-Device Speech Transcription in React Native with Apple SpeechAnalyzer

This post introduces speech transcription support in React Native AI, implemented using Apple’s SpeechAnalyzer and SpeechTranscriber APIs available in iOS 26. It explains how to use the AI SDK’s transcribe function to pass audio buffers, how modular analysis is configured through the SpeechAnalyzer class, and how system-level asset management ensures models are handled outside the app bundle.
cover
Jul 30
·
Article

On-Device Text Embeddings in React Native With Apple NLP Framework

Our React Native AI library now supports on-device text embeddings by integrating Apple's native Natural Language framework. This implementation leverages the NLContextualEmbedding model built directly into iOS. Because the model is treated as a shared operating system asset, it enables powerful semantic features without requiring developers to bundle large files or force users to perform any extra downloads. We expose this capability through our Vercel AI SDK provider, simplifying integration for React Native developers.
cover
Jul 25
·
Article

Expanding On-Device Apple LLM Capabilities: Introducing Tool Calling

We’ve just added tool calling to our Apple provider for the AI SDK, unlocking the ability to run custom functions directly within Apple’s on-device language model. This means your React Native apps can now generate dynamic, interactive content, like fetching live data or executing app-specific logic, without ever leaving the device.
cover
Jul 14
·
Article

On-Device Apple LLM Support Comes to React Native

Apple’s on-device LLM is now available in React Native, enabling developers to build private, fast, and offline AI features powered by Foundation Models. This preview release supports text generation, streaming, structured outputs, and first-class support for Vercel AI SDK. A stable version is planned for release alongside iOS 26 later this fall.
cover
May 28
·
Article

Want to Run LLMs on Your Device? Meet MLC

Running LLMs locally on mobile isn’t a fantasy-it’s possible with MLC. This post explains how MLC compiles both model and runtime to create optimized, cross-platform packages for local inference. Discover what’s required, how it works, and why MLC stands out among edge ML frameworks.
cover
May 15
·
Article

Meet react-native-ai: LLMs Running on Mobile, for Real

Running AI models locally in React Native used to sound impossible, but not anymore. This post introduces react-native-ai, a new library powered by MLC and integrated with Vercel AI SDK, enabling on-device LLM inference with a web-like API and native performance.
cover
Mar 11
·
Article

Local LLMs on Mobile Are a Gimmick-For Now

Running large language models directly on mobile devices is currently limited by model size, format compatibility, and performance trade-offs. However, tools like MLC are emerging to simplify the process and pave the way for a future where everyone has their own AI assistant in their pocket.
cover
Dec 1
·
Article

Creating a Video Transcription App: Lessons Learned

Callstack shares lessons learned from building a video transcription app using OpenAI's Whisper for speech recognition. The guide covers extracting audio, generating transcripts, speaker diarization, and testing different Whisper model sizes to optimize for speed and accuracy.
No items found.
cover
Mar 19
·
Tutorial

The Hard Way vs. The React Native AI SDK Way: Stop Writing Custom Modules for Every Model

Learn how React Native AI uses a unified provider model to switch between cloud and on-device LLMs without rewriting application logic, enabling reliable AI experiences online and offline.
cover
Mar 12
·
Tutorial

Build Smarter Apps: Tool Calling & AI Orchestration Explained

Learn how on-device models in React Native can call tools, interact with external APIs, and return structured outputs you can use directly in application logic.
cover
Mar 5
·
Tutorial

MLC LLM + React Native: On-Device AI Without the Pain

Learn how to run third-party on-device LLMs in React Native using MLC LLM. Choose your models, run them efficiently across platforms, and keep a unified JavaScript API with React Native AI.
cover
Feb 24
·
Tutorial

Intelligent Fallbacks with Apple Intelligence in React Native

Learn how to use Apple’s built-in Foundation Models in React Native apps, reduce memory usage, and enable fast, fully on-device AI with React Native AI Apple.
cover
Feb 10
·
Tutorial

What Is the React Native AI SDK? A Complete Intro & Quickstart

Learn why on-device AI matters for React Native apps, how local LLMs behave offline, and what problems React Native AI is designed to solve from day one.
cover
April 20, 2026
·
Event

Ambient Generative AI: Deploying Latent Diffusion Models on Mobile NPUs

Join Lech Kalinowski at AI Engineer Miami on April 20–21 for a talk on running offline latent diffusion models on mobile NPUs.
cover
March 12, 2026
·
Event

React Native Evals: Measuring AI Code Quality in Practice

React Native Evals introduces a data-driven way to measure how AI coding models perform on real React Native development tasks.
cover
January 29, 2026
·
Event

LLM Inference On-Device in React Native: The Practical Aspects

A practical look at reliability, performance, libraries, and tradeoffs when running LLM inference locally in React Native apps.
cover
December 5, 2025
·
Event

The Offline AI: On-Device LLMs in React Native With AI SDK

Learn how to run on-device LLMs in React Native using Vercel’s AI SDK from Michał Pierzchała's talk at DevAI by Data Science Summit.
cover
November 28, 2025
·
Event

How to Run Any LLM On-Device With React Native

In this talk, Szymon will show how to run LLMs directly inside React Native apps using an AI SDK that provides a powerful abstraction layer to simplify building AI applications. Join him as he explores react-native-ai, a library that enables local LLM execution.
cover
September 2, 2025
·
Event

React Native AI: Bringing On-Device LLMs With AI SDK

Need offline AI in your mobile app? This talk recording demonstrates how to use the AI SDK to create a custom provider for on-device LLMs in React Native, ensuring privacy and functionality anywhere.
cover
September 2, 2025
·
Event

AI Meetup in Wroclaw with Callstack & Vercel

On Sept 2 in Wrocław, join top speakers from around the world at the AI Meetup. Learn about AI SDK 5, on-device LLMs in React Native, TV-ready apps with Kiro.dev, and how AI supports developers beyond code.
June 10, 2025
·
Event

Live Dev Session: First Impressions of Apple’s On-Device AI

Tune in to dev chat on Apple’s AI SDK, iOS 26 naming chaos, Siri’s limits, Liquid Glass UI, and on-device LLMs.
June 3, 2025
·
Event

Run LLMs Locally With React Native & MLC

Watch how MLC brings on-device AI to React Native. See react-native-ai in action and discover what’s next for local model execution.
July 25, 2024
·
Event

Bringing AI to React Native

Leveraging capabilities of local devices to run LLMs via React Native and Vercel AI SDK.