--- title: "Custom & Private Models" description: "Standard hosted models do not fit every product or data environment. We deploy private and self-hosted models where teams need tighter control or models adapted to product-specific data and workflows." url: https://www.callstack.com/capabilities/custom-private-models updated: 2026-11-06T10:07:17.296Z --- # Custom & Private Models Standard hosted models do not fit every product or data environment. We deploy private and self-hosted models where teams need tighter control or models adapted to product-specific data and workflows. _[Agentic Delivery](https://www.callstack.com/agentic-delivery) › Custom & Private Models_ **Use the right AI model, locally or in the cloud.** Standard hosted models do not fit every product or data environment. We deploy private and self-hosted models where teams need tighter control or models adapted to product-specific data and workflows. [Book consultation](https://www.callstack.com/contact) [Explore services](#services) Trusted by 100+ Enterprise clients Expensify · Ticketmaster · DirecTV · MLS · PWC · Evernote · AutoZone · MoMo · Dream11 · Rainbow · Futurewei · RIMAC · Hello Fresh · Haaretz · ForaTravel · CelcomDigi · Teamworks · Boats · Questrade · Dialogue Why deploy with Callstack ## Better model output. More control. We evaluate where hosted models fall short, then deploy private, self-hosted, regional, or hosted models around your data, latency, security, and workload needs. - **Keep sensitive data off third-party systems.** Self-hosted 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](https://www.callstack.com/services/on-premise-llm-deployment): Stand up self-hosted models so sensitive code and data never leave your infrastructure. - [LLM Fine-Tuning](https://www.callstack.com/services/llm-fine-tuning): Fine-tune models on your codebase, conventions, and domain so outputs match how your teams actually build. - [Model Evaluation](https://www.callstack.com/services/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](https://www.callstack.com/contact) Scope → Build → Scale ## Deploy models where the workload fits. ### Scope We select a product workflow, define where agents act, and agree the controls and success measures. - Workflow and owners defined - Baseline and controls agreed - Token budgets confirmed ### Build We connect context, agents, and verification to your tools, then run the workflow on your product backlog. - Running on your product backlog - Speed and quality measured - Business impact validated ### Scale We document the workflow, transfer ownership, and extend it across teams and products based on results. - Your team owns the workflow - Expand based on results - Full knowledge handover - [30/31 Next.js tasks as pixel canary · 85% Lower inference cost vs Opus 5.5](https://apex.callstack.com) - Industry runs on our tooling · 50M+ OSS downloads / month - 100+ Enterprise projects delivered - React Foundation Founding Member · 300+ commits to React Native · Contributing since 2016 - ISO 27001 certified - [32 Models tested against React Native](https://rn-evals.vercel.app) 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](https://www.callstack.com/contact) Open Source ## Build with our open-source tools. We open-source the tools behind our delivery model. Use them, fork them, or let us run them for you. [Check All Tools](https://www.callstack.com/open-source) - [React Native AI](https://github.com/callstackincubator/ai): On-device LLM execution in React Native with Vercel AI SDK compatibility (227.7K downloads/mo) - [React Native Evals](https://github.com/callstackincubator/evals): A benchmark suite for evaluating how coding models solve real React Native tasks (111 stars) - [Skill Gym](https://incubator.callstack.com/skillgym/): Prove your agent skills work before you ship them (1.6K downloads/mo) Insights ## Worth your time, by engineers. [Explore Insights](https://www.callstack.com/insights) - [Quantization Impact on LLM Quality: A Case Study of Apex](https://www.callstack.com/events/quantization-impact-on-llm-quality-a-case-study-of-apex-a-gemma-based-model) (Nov 4 · Talk): Artur Morys-Magiera and Lech Kalinowski share findings from 344 benchmark runs with Apex, our Gemma-based LLM, examining the trade-offs between model size, decode speed, and quality. - [Conversational Banking: From Customer Questions to Authorized Actions](https://www.callstack.com/blog/conversational-banking-from-customer-questions-to-authorized-actions) (Nov 2 · Article): How does a banking assistant turn a customer’s question into an authorized action? Follow an unfamiliar payment from transaction lookup to card freeze and specialist handoff, exploring how models, banking services, and human teams work together and what the bank needs to control at each step. - [Apex Is Now Generally Available: Agentic Coding Model for Mobile and Web, Specialized in React](https://www.callstack.com/blog/apex-agetic-coding-for-mobile-and-web-spcialied-in-react) (Oct 1 · Article): Apex is now publicly available. Built by Callstack, it brings React Native expertise to feature development, code reviews, debugging, and testing, with strong performance on Next.js tasks too. See the benchmark results, compare API pricing, explore self-hosting options, and get started with Apex in your own project. - [Can Jev Make AI Agent Decisions Faster?](https://www.callstack.com/events/can-jev-make-ai-agent-decisions-faster) (Oct 1 · Live Stream): Explore Jev with Kewin Wereszczyński and Szymon Chmal: how it works, its approach to faster agent decisions, and possible local alternatives. - [No Framework, No Server: Making AI Agents Collaborate in One Terminal](https://www.callstack.com/events/no-framework-no-server-making-ai-agents-collaborate-in-one-terminal) (Sep 15 · Talk): Lech Kalinowski will show how Agents Commander lets multiple AI coding agents collaborate directly in one terminal without a central server or heavyweight framework. - [What Apex shows about React Native AI models](https://www.callstack.com/events/can-a-specialized-model-beat-frontier-models-at-react-native) (Aug 13 · Live Stream): See how Apex, Callstack's React Native model, compares with frontier models on navigation, animations, async state, and performance-heavy UI work. - [On-device AI After WWDC 2026: What's New?](https://www.callstack.com/blog/on-device-ai-after-wwdc-2026-whats-new) (Jun 8 · Article): 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. - [Optimizing Self-Hosted Gemma for Production Inference](https://www.callstack.com/blog/optimizing-self-hosted-gemma-for-production-inference) (Jun 5 · Article): 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.