
Run private AI where users are.
Private by default
Inference stays on device, so sensitive data never leaves the phone and privacy-first features need no network call.
Optimized runtime
A runtime and model format chosen for your hardware, keeping inference fast, stable, and memory-safe in real use.
Fine-tuned to your domain
We adapt models with LoRA without full retraining, for fast, cost-effective customization to your use case.
Safe model deployment
Background delivery, versioning, and rollbacks let you push new models without shipping a full app release.
Hybrid execution
Routes complex requests to server models when more compute or context is needed, with on-device as the default.
Benchmarked per device
Measured latency, memory, and battery across device tiers, so behavior is predictable on real hardware.
Assess → Deploy → Operate
Deploy models where the workload fits.
Assess
We assess models, controls, and exposure. Leadership gets a clear approval path.
Deploy
We deploy models, workflows, and guardrails. AI runs under the controls it needs.
Operate
We keep the setup ready for the next review cycle. Models, policies, and controls stay up to date.
Case studies
What shipping at AI speed looks like
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.

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.
39M+
Downloads / month67K+
GitHub stars300+
React Native commits100+ 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.


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

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.
39M+
Downloads / month67K+
GitHub stars300+
React Native commits100+ 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.


We are Codex Ambassadors.
We run meetups, workshops, and hands-on sessions that help teams learn Codex and apply it in real work.
Let’s find the right path for your product.
Whether you’re planning new work or unblocking an existing product, we’ll help you choose the right path forward.
Which devices can run on-device AI?
Most modern iOS and Android devices support on-device inference. We benchmark your target devices early to identify any constraints.
How large can the models be?
It depends on the device and use case. Small models (under 1GB) work well on most devices; larger models may require newer hardware or compression.
Will on-device AI drain battery?
It can if not optimized. We profile power consumption and apply optimizations to keep inference efficient for real-world usage.
Can I update the model after the app ships?
Yes. We design update strategies that let you push new models without requiring a full app release.
What happens if the device can’t run the model?
We design fallback strategies, such as using smaller built-in models or routing to the cloud when needed.
Do you support both iOS and Android?
Yes. We choose runtimes optimized for each platform while ensuring consistent behavior across your user base.
Can on-device models be customized for my domain?
Yes. We use techniques like LoRA fine-tuning to adapt models to your use case without full retraining.
How do you handle older devices?
We benchmark across device tiers and recommend which models and runtimes work for your minimum supported hardware.
Where does our data live, and who owns the models?
Inference stays on the device, so sensitive data never leaves the phone and privacy-first features need no network call. The models run locally on your platforms and are yours to own.
Own your models. On every device.
From runtime selection to optimization and rollout, we get private AI running locally across your platforms.
I recommend them as a trusted tech partner for running complex projects.
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.
Insights
































