Sviatoslav Oleksiv

AI SaaS Solution Architect · Kraków, Poland

I re-architect SaaS for the next 100 customers.

Solution architect for SaaS teams whose product has outgrown its first architecture: an AI-built MVP, a contractor codebase, or a platform that now has to scale. I re-architect on AWS, Next.js and Postgres/Supabase, and I can own the roadmap as your fractional CTO.

Start with an architecture reviewSee case studies
Sviatoslav Oleksiv, waist-up portrait in a black t-shirt
3 years
lead engineer of a multi-tenant AI SaaS in Germany
1,600+ hours
longest Upwork contract, still active
211 customers
paying for a micro-SaaS I founded and run alone
Top Rated Plus
100% Job Success, $200K+ across 23 contracts

What I do

Four ways to work with me.

  • Architecture review

    Fixed price · one week

    A written report covering tenant isolation, database schema and migrations, background jobs, webhook reliability, auth and row-level security, cloud spend, and a prioritized refactoring plan for your next 100 customers. Works for code generated with Cursor, Lovable, Bolt.new or Replit as well as agency-built platforms.

  • Re-architecture and scaling

    I take fragile codebases and make them production-grade: idempotent background jobs, validated LLM outputs, PostgreSQL and Supabase row-level security, Stripe billing edge cases, Playwright end-to-end tests, CI/CD on AWS and Vercel.

  • Fractional CTO

    Weekly roadmap planning, PR reviews, hiring support, and architecture decisions explained in plain English. You work directly with me in CET with daily US overlap. Nothing is subcontracted.

  • AI systems

    LLM agents and tool integrations with Anthropic, OpenAI, Gemini and MCP, plus media and data pipelines at scale: image, video and voice generation with ElevenLabs, Replicate and Remotion on AWS Lambda.

  • AWS
  • Vercel
  • Next.js
  • TypeScript
  • Node.js
  • NestJS
  • Python
  • PostgreSQL
  • Supabase
  • MongoDB
  • Stripe
  • Anthropic
  • OpenAI
  • Gemini
  • MCP

Case studies

“Sviat was a pleasure to work with - professional, reliable, and incredibly fast without compromising quality. I'd gladly hire him again.”

Adrian Hanrath, LIVEDAB

Lead Engineer · Dec 2023 to present

LIVEDAB

Event-marketing SaaS where visitors turn their photos into branded AI images and videos.

Lead engineer since 2023, owning architecture, delivery and production: AI image and video generation, multi-tenant teams, CRM and GDPR. I moved the AI chain from the visitor's browser into a durable server-side workflow, so a closed tab no longer kills a job.

Campaigns reach 30 to 60% visitor usage at major German trade fairs.

  • Next.js
  • TypeScript
  • AWS
  • Remotion
app.livedab.com ↗

“Sviatoslav is one of the few I kept on for close to a year, which tells you most of what you need to know.”

Emiel Cockx, Genvision

Full Stack Engineer, part-time · Apr 2025 to Oct 2026

Genvision

Public data platform with a geospatial layer, with an AI team building agents on top.

A founder-built codebase with AI-generated PRs. I owned the front end and API, decided what could merge, and set the codebase rules that made generated code fit. When a tile-generation script started racking up cloud costs, I found the cause and fixed it.

650 hours over 18 months, a map API the AI team plugged into their agents, and a step-by-step handover.

  • Next.js
  • AWS
  • PostGIS
  • Vector tiles

Founder and sole engineer · May 2026 to present

mosfoto.com

Paid photo tool for Polish residence-permit applications. Live in four languages, profitable.

Founder and sole engineer: product, code, payments, support and content. Pay-per-result on Stripe, a free watermarked preview before any payment, and a full refund if the office rejects the photo. The place I learned unit economics and cloud spend first-hand.

Profitable. 211 paying customers in October 2026, 8,500+ photos prepared.

  • Next.js
  • Stripe
  • Replicate
  • PostgreSQL
  • Vercel
mosfoto.com ↗

“I've worked with him on 2 separate projects now. He continually seeks to improve his skills and deliver above expectations on any project.”

Michael Ochs

Senior Full Stack Engineer · May 2024 to Feb 2025

Fintech lending platform

Commercial-lending web app with multi-step loan application flows.

Two contracts for the same client, about 700 hours. I built key components of the core application in Next.js and modelled the loan flows as XState state machines, so every step, validation and resume path is explicit and testable. The second contract moved the platform onto Azure.

Both contracts rated 5.0, and the client came back for the second project.

  • Next.js
  • TypeScript
  • XState
  • Azure

Own project · Jul 2026

Personalized AI sales videos

One command renders a personalized sales video for each prospect.

From a company name, website and city: Playwright records the prospect's live site, Claude writes a demo call script constrained by the production voice agent's system prompt, ElevenLabs voices both sides, and Remotion composes footage, audio and captions.

A per-prospect MP4 in one command, with a script-only mode for review before paying for voices and rendering.

  • Remotion
  • Claude
  • ElevenLabs
  • Playwright

How I work

How I work

  1. 01

    Tests define correctness, not the agent

    I use Claude Code and Cursor daily behind strict test suites, codebase rules and MCP tooling. Requirements become tests, the agent writes code against them, and nothing merges until the loop is green. Generated code scales with the project instead of turning into debt.

  2. 02

    Re-architect, don't rewrite

    AI-built MVPs and contractor codebases usually work as prototypes and struggle with real users, payments and traffic. I keep what works, fix the risky parts first, and skip the rewrite unless it is actually needed.

  3. 03

    You work with me, not a middleman

    No agency, no subcontractors. I explain architecture decisions in plain English and own the result, not only tickets. Based in the EU, working in CET with daily US overlap.

What clients say

Long engagements, repeat clients.

  • “He put real thought into working with AI coding tools, setting up rules and structure in the codebase so the generated code actually fit.”

    Emiel CockxGenvision, 650-hour contract

  • “One of the best freelancers I've worked with on Upwork. Highly skilled, reliable, always responds quickly.”

    Hannes Meine16 months of code review and backup engineering

  • “If you're looking for someone who not only knows React and Next.js, but is also a trustworthy and reliable partner, Sviat is the person you need.”

    Michael OchsFintech, multi-step loan flows, 392-hour contract

  • “Sviatoslav is brilliant - a full stack dev who thinks through UX issues on his own and comes up with clever solutions. A talented engineer with a great product mindset.”

    Upwork clientChrome extension for LinkedIn, 2024

  • “Sviat is an amazing FSD. He's a great communicator, hard worker, and fast learner. Anyone looking for a full stack developer will be very happy to work with Sviat.”

    Upwork clientAI SaaS MVP, 358-hour contract

  • “Great to work with him. Quick results and very experienced in what he does. I will hire him again!”