Stefan Oleksiienko

Sviatoslav “Stefan”
Oleksiienko

I build new systems,and I fix the onesnobody else will touch.

Notre Dame computer science, class of 2027. Born in Dnipro, Ukraine.

firstintern ClickUp ever hired, at ~$4B, by exception from their co-founder and CTO. A P0 vulnerability found six days in.
20M+people reached by backend changes I cut over myself. Zero outages.
100%of the students who finished the accelerator I founded at Notre Dame landed offers: NVIDIA, AWS, Boeing, IBM, Visa.
92%of a 17,000 line open source system monitor is my code, written leading a team of four.
01

Out of Ukraine

I have been programming since I was eleven: web apps, networks, embedded systems, security, whatever I could get near. A proximity unlock system I built took first place at Ukraine's state robotics competition. I wrote competitive programming with my lyceum's team. At sixteen, Genesis Tech, one of Ukraine's largest tech companies, admitted me to its startup school as the youngest in its history, and after finishing an Argonne National Laboratory training program in nuclear science I did my own research into synthesizing a medical isotope from nuclear plant waste.

Then the war reached Dnipro. I learned the nuclear power station near my city had been shelled while sitting in the basement of a bomb shelter; later, the first ICBM ever used in war landed a quarter mile from my house. We drove out: ten days from Dnipro to Alanya on the southern Turkish coast, sleeping at gas stations and border crossings, wherever the road allowed; I spent the ride reading Hawking’s A Brief History of Time. From Turkey, at seventeen, I cold emailed hundreds of boarding schools until one in Iowa gave me a full ride. A year later I got into Notre Dame as a QuestBridge Scholar. I tell you this not for sympathy but because it is the same method you will see on every screen below: when the front door is shut, I write to everyone who owns a side door, and I do the work when one opens.

DNIPRO ALANYA FAIRFIELD, IOWA NOTRE DAME ATLANTIC
Ten days by road, Dnipro to Alanya. A year of cold emails. Fairfield, Iowa; then Notre Dame.
age 11First code. Web apps, then networks, embedded systems, security.
lyceumFirst place at Ukraine's state robotics competition; competitive programming with the school team.
2021Argonne National Laboratory training program, then my own isotope research.
age 16Youngest admit in the history of Genesis Tech’s startup school.
2022War reaches Dnipro. Ten days on the road to Turkey; hundreds of cold emails; a full ride in Iowa answers.
2023Notre Dame, as a QuestBridge Scholar.
02

Notre Dame

Computer science, GPA 3.868, graduating May 2027. In my second year Visa selected me for the inaugural Visa Fintech Foundation cohort: I researched CBDC and stablecoin integration for the US market and presented the findings to Visa's C-suite, where I met CEO Ryan McInerney. That relationship compounded: Visa is now moving to sponsor the accelerator I run at Notre Dame. This fall I also start undergraduate research in Notre Dame's S2E security lab, finding vulnerabilities with machine learning.

selected by

VISA
03

What I built while studying

Three things, overlapping. A company I co-founded and built the engineering of end to end, a founding engineer sprint at a second startup, and a programme that turned Notre Dame's best students into placed engineers.

Tweeds/2024–2026/co-founder, founding engineer internal, not public

Built the production pipeline that replaced a four week manual process with minutes

The product turned a book manuscript into a finished, search optimised Amazon listing; publishers were paying a copywriter and waiting about four weeks per book. For two years I built and ran the engineering end to end by myself: 35K+ lines of backend Python, the React frontend and admin dashboard, 1,000+ test functions, 15 database migrations in production, the CI/CD and the cloud infrastructure. Then I hired and ran the interns who maintained it.

4 weeks → minutesturnaround86Krow corpus4interns hired and managed

scrapebrightdata
extractspacy, keybert
retrievepgvector
generaterouted llm
publishcelery
was ~4 weeks by hand2 to 8 s per book

Independently runnable stages with typed data between them, so any one can be rerun without replaying the rest.

The hard parts, specifically

Amazon's category taxonomy has ~14,000 nodes and shifts under you. I designed the categorisation algorithm that survives that: embedding retrieval plus union find clustering on cosine similarity, so listings stay correctly placed as the taxonomy changes underneath.

LLM routing as infrastructure: a provider agnostic layer across Claude, OpenAI and Gemini with schema validated structured outputs, automatic retry on validation failure, and per call cost tracking. Scraping ran under cost governance: idempotency keyed jobs and daily budget caps enforced in cents.

Security was audited, not asserted: I closed the audit by shipping row level security across 13 tables and a prompt injection guard on LLM inputs.

Beyond the code: interviewed 12+ candidates from 60+ applicants, wrote the code review rubric and CI gates, promoted the strongest hire to subsystem lead, and wrote the architecture decision records.

Desync AI/summer 2026/founding engineer internal, not public

Merged 260+ pull requests in my first month as a second startup's founding engineer

A Rust, Python and Postgres platform. I owned the plumbing a product stands on: payments and billing, CI/CD and deployment automation, observability, security hardening, and GPU infrastructure for self hosted 70B model inference on an H100 cluster. Product side: an async streaming chat agent, and a feature flag system with safe rollout controls.

260+PRs in month one70Bself hosted inferenceH100cluster

productAsync streaming chat agent; a feature flag system with safe rollout controls.
gpu infraSelf hosted 70B model inference on an H100 cluster.
paymentsPayments and billing.
ci/cdDeployment automation, commit to running service.
observabilityLogging and metrics across the platform.
securityHardening across the stack.

Founding engineer scope, drawn out: one person owning every layer at once. That is where the 260+ first month pull requests went.

The founder track that came with it

The same summer, Notre Dame's Race to Revenue accelerator selected me as a founder with a $6,000 grant; I built the product the venture went to market on and pitched at Chicago Tech Week, working the accelerator's investor and operator bench through its sales curriculum: prospecting, discovery, close.

Then I founded the Innovation Sprint Lab: a student accelerator where teams ship production software for real companies under weekly sprints and mentorship from senior industry engineers. I built it by convincing people who had no reason to bet on a sophomore: Justin Hintz, a VP at Teamworthy Ventures, and the founder of a $4B company invested their time, a veteran VC at a large DC fund funded it, and the IDEA Center gave it a home. My idea, my programme.

Flywheel: students ship real software, get placed, companies return
The loop the lab runs on: students ship, finishers get placed, the companies come back with harder problems.

Fall 2025 cohort/the first one/proof of model public post

Seventy applied, fifteen got in, and every one who finished landed a job

70applied
27technical interviews, run in days
15selected, waitlist still active
100%of finishers placed

Placements went to NVIDIA, AWS, Boeing, IBM and Visa. Several arrived already carrying experience from places like the CIA and 84.51°.

Who mentored them, and what shipped

ClickUp mentored two teams directly, through co-founder and CTO Alex Yurkowski. Teamworthy Ventures embedded a third team inside a portfolio company's codebase, with its VP Justin Hintz plus an ex-Meta engineer. The bench also carried a CTO in Residence who had been a WebMD director of engineering and a Y Combinator co-founder, and a Notre Dame adjunct professor who leads product at a studio.

At Demo Day the investor Tim Connors joined Alex and Justin to give teams direct feedback. Alex publicly congratulated the top performers; Justin put up a cash prize for the strongest student. ClickUp offered to fast track hiring, Teamworthy offered portfolio company introductions.

One team shipped Smart Invoice AI and cut a partner's invoicing time by more than 80%.

where the finishers went

NVIDIAAWSBOEINGIBMVISA

SprintHack@ND/nov 2025/ai workflow named reference

Ran a hackathon as a talent funnel, and got industry to judge it

A talent funnel disguised as a weekend. Judged by a venture investor, Google and Amazon alumni.

$5Kprizes raised12teams60+participants14judges

judged and sponsored by people from

GoogleAmazonReplitEY

2026–27/next/full year programme committed, not yet run

Unified four campus organisations, about 300 students, into one programme

Now the lab turns outward, to grow the region's tech ecosystem: local businesses get engineering they could not hire, and the engineers get a reason to stay. Four clubs that had never run anything together share one cycle, kicking off with an open hackathon October 3–4. Goodwill Michiana is the first embedded partner: a team ships their first automation this semester (a weekly vendor report that costs a full day by hand) inside their plan to scale from $50M to $100M, mentored weekly by Goodwill's CEO and an ex-Amazon technical PM. September opens the year with lectures and mentorship sessions; the booked speakers so far include a startup lawyer, a high frequency trader, and an engineer from GitHub.

~300students unified4organisations60+businesses asking

Septlectures and mentorship sessions
Oct 3–4kickoff hackathon, open to all
Oct–Decsprint lab cohort
early Decdemo day
Dec–Marventure competition track
Jan–Aprspring commercial build
Apr 22final showcase

A full academic year, ending in a showcase that feeds the strongest teams into the university's summer accelerator.

04

Then ClickUp made an exception

ClickUp, a roughly $4B company, had never taken an intern. Their co-founder and CTO Alex Yurkowski broke that policy for me in the summer of 2026. Six weeks on the platform team; here is what happened in them.

ClickUp/2026/week one internal, not public

Found a P0 security vulnerability in my first week

Six days into a company that had never taken an intern, in a codebase I had not written.

P0highest severitywk 1found in

ClickUp/2026/platform internal, not public

Moved thousands of feature flag definitions through production cutover inside a two minute freeze window

The platform every engineer ships features through. I ran the cutover myself.

<2 minfreeze window0outages20M+people reached1,000+engineers served3environments

env 1env 2env 3 · cutover

The bar is the migration. The ochre mark is the production freeze, drawn to scale: under two minutes. Everything either side of it served traffic normally.

How it was verified

Seven stacked reviewed pull requests, roughly 900 lines of production code against roughly 2,900 lines of tests.

Byte-exact verification across about 1,900 field values, plus zero-write idempotency checks against a staging replica I built myself, before every release.

The related sync enriched about 3,400 flag records with eight metadata fields.

The design principle behind all of it: make every step small, reversible and independently verifiable, and the scary cutover becomes routine. That is the tradeoff I will defend in any system review.

ClickUp/2026/integration internal, not public

Caught an undocumented vendor API behavior that would have silently corrupted every running experiment

Undocumented, silent, and only under load. I drove it into the vendor's own engineering org until they shipped a fix.

everyrunning experiment at risk~900req/min ceiling proven0dropped writes

What else the probing found

Three further undocumented API contract requirements, found by empirical probing rather than documentation, with fixes contributed back.

Load-tested the real rate ceiling at a sustained ~900 requests per minute with zero dropped writes, which is the number the cutover plan was built on.

ClickUp/2026/rescue internal, not public

Restored CI that had failed every pull request for months, and took the suite from 139 tests to over 530

Nobody had touched it in months, so nobody could change anything safely.

139 → 530+tests24PRs in 4 weeks10dependency vulns patched

What I changed about how it ships

Four of the ten dependency vulnerabilities were high severity.

Alongside the test suite I introduced automated AI code review on the repository, so the standard held after I left rather than decaying back.

ClickUp/2026/agents internal, not public

Turned an org wide flag audit into a production agent with canary gates and a no writes on uncertainty policy

Canary verified gates and a no-writes-on-uncertainty policy, so it fails closed.

330xless alert noise4repositories8further agent skills

Why the 330x number holds

It was justified against a thousand recorded production run durations, not a sample.

It then survived a 79 minute scheduler delay in production that would have broken the alternative design I had rejected.

05

See for yourself

The ClickUp work is behind private repositories; you have to take my word for it. These you do not. Each was cloned, built and run on my machine, and everything below is real output. This is for whoever you forward this to.

CoreMetrics/C++23, SDL3/macOS, linux, windows repo, LGPL

Wrote a widget toolkit on raw pixel surfaces, then a cross platform system monitor on top of it

A system monitor with no UI framework underneath: no Qt, no Electron, no Skia. Text layout, hit testing, event dispatch, redraw; I rasterised every glyph and line on screen myself. The About tab paints the app's own live footprint, so every screenshot doubles as evidence.

92%of the source, mine1.6 MBon disk33test suites3platforms in CI

CoreMetrics cycling through its System, Processes and About tabs
System, processes, about. Every frame is a real paint, produced by the binary's own headless screenshot mode.
The design worth a look

Four person Notre Dame software engineering team, three months, per developer branches behind a PR template and required review; I led it and wrote most of the source.

The widget hierarchy uses CRTP: every element inherits Cloneable<Self> rather than the base directly, so a deep clone() and a covariant cloneDerived() come for free instead of being written out per class.

mini-allocator/C/malloc, free, realloc, calloc repo, MIT

A drop in allocator with segregated free lists, and a test suite that proves it

Segregated free lists, boundary tags, coalescing on every free through the footer trick.

883assertions pass0failures6size classes

mini-allocator · make test
$ cc -Wall -Wextra -O2 -std=c11 -c allocator.c
(no warnings)
$ ./build/test_allocator
mini-allocator: running tests
  -> test_small_alloc
  -> test_large_alloc
  -> test_coalesce
  -> test_fragmentation
  -> test_realloc_grow      (and shrink, from-NULL, to-zero)
  -> test_calloc_overflow
  -> test_stress

--- summary ---
  bytes from OS    : 1114160
  bytes in use     : 0
  allocations      : 2913
  frees            : 2913
  splits           : 2977
  coalesces        : 2811
passed: 883   failed: 0
header 16 B payload, 16 B aligned footer 8 B low bit of size = allocated size mirror, makes coalescing O(1) FREE LISTS ≤64 B≤128 ≤256≤512 ≤1024>1024 first fit inside a bucket, escalate to the next on no fit

The footer exists so a free block can find its left neighbour in constant time. That one trick is what makes coalescing on every free affordable.

microshell/C, ~1K LOC/no libreadline repo, MIT

A POSIX shell with real job control, written from scratch

Real job control: the first child of a pipeline becomes group leader, later stages join, and the parent sets it too so the race is closed.

30/30tests pass~1Klines of C0third party deps

microshell · live session
microshell> ls src | grep c$ | wc -l
       6
microshell> echo building > f.txt && cat f.txt
building
microshell> false
microshell> echo status=$?
status=1
microshell> export WHO=stefan; echo hello $WHO
hello stefan
microshell> sleep 2 &
[1] 31458
microshell> jobs
[1]  Running		sleep 2 &
microshell> exit
$ bash tests/integration.sh
integration.sh: 14/14 ok
$ bash tests/test_parser.sh
test_parser.sh: 16/16 ok

chat over a message queue/C, pthreads/producer consumer repo

A concurrent message queue client, stress tested with twelve threads fighting over it

A thread safe blocking queue under a pub/sub client: mutex and condition variable, timed waits, and a shutdown broadcast so blocked consumers wake and exit clean instead of hanging forever. Background pusher and puller threads move requests over HTTP long polling; a terminal chat app rides on top.

8×4producers × consumers4,096messages, none lost5/5unit tests

chat-application · make + tests
$ make
Compiling src/client.o src/queue.o src/request.o ...
Linking   lib/libsmq.a
Linking   bin/chat
$ for t in 0 1 2 3 4; do bin/unit_queue $t && echo "$t PASS"; done
0 PASS  queue_create
1 PASS  queue_push
2 PASS  queue_pop
3 PASS  queue_delete
4 PASS  queue_shutdown
$ bin/test_queue 8 4 4096  # 8 producers, 4 consumers
exit 0 · all 4,096 requests accounted for · 12 ms
$ bin/test_client localhost 9620  # end to end, live pub/sub server
exit 0

nd-canvas-study/python/browser automation, llm, vector search repo

Turned a university course portal into an exam prep pipeline, one command deep

Give it a class name. It defeats single sign on and Duo with a real browser, pulls the whole course, then works out what you are least prepared for. The study path is a topological sort, so a topic appears only once its prerequisites do.

13pipeline operations23topics ordered269problems tracked

The tool running on a real course: thirteen pipeline operations, and a topologically ordered study path across 23 extracted topics
Running on a real course. Thirteen pipeline operations, 23 topics extracted and ordered by prerequisite, 269 problems tracked.
nd-canvas-study · one command
$ python prep.py "statistics"
 Canvas session OK
Matched 'statistics' → [128781] Statistics (score 1.00)
... download, bundle, gap analysis, problem extraction ...
vector index ready
inherited service530+
mini-allocator883*
coremetrics175
microshell30

Tests I wrote, per project. The inherited service started at about 139 with a red build on every pull request. *Assertions rather than cases.

Underneath it all: TypeScript and Python daily; C, Rust and C++23 when the problem calls for them. A filesystem in safe Rust on crates.io, a RISC-V assembly suite, an email pipeline that cut analysis time 99.7%.

the toolbox

languages

TypeScriptPythonJavaScriptRustCC++23BashRISC-V asm

backend

FastAPINode.jsExpressDjangoCelery

ai and llm

PyTorchspaCyKeyBERTpgvectorlitellmpydantic-ai

data

PostgreSQLRedisSQLiteMongoDB

frontend

ReactNext.jsViteTailwind

infra and tooling

DockerAWSVercelRailwayNginxGitHub ActionsSentryPlaywright
06

The ask

I am looking for an engineering seat: AI systems, backend, full stack, or security. On security I will be straight: I am not a career researcher, I am the engineer who found a P0 in week one, closed an audit by shipping row level security in production, and starts vulnerability research this fall; point that at your problem and it compounds. I want to build the new thing, the agent plumbing, the inference infrastructure, the product that does not exist yet; and I am just as good at the hard, unglamorous work that keeps it all standing. Part time now, full time from June 2027.

start_part_time_now evaluating Available
full_time_from_june_2027 evaluating Available
visa_sponsorship evaluating Required

Two of those I control. The third only a company can flip: I am an international student and will need H-1B sponsorship for the full time seat. Part time now is the cheapest way to find out if I am any good.

their problem, already solved once

A migration everyone agrees is necessary and nobody will own

Because the downside is an outage on your busiest system and the upside is that nothing visibly changes.

done

Ran one through production cutover myself across three environments. Freeze window under two minutes, zero unresolved errors, zero outages, on the platform 1,000+ engineers ship through and 20M+ people depend on.

A vendor whose API will corrupt your data quietly

Undocumented behaviour that no test catches because it fails silently and only under load.

done

Found one mid migration that would have corrupted every running A/B experiment. Drove the escalation into the vendor's own engineering org until they shipped a fix, then designed the joint cutover both companies ran.

A service the team is quietly afraid of

Red CI, no coverage, an owner who left. Every change to it is a coin flip, so changes stop.

done

Took an inherited service from a build that failed every pull request for months to 530+ tests from about 139, added timeouts and backoff on all third party calls, and merged 24 pull requests in four weeks.

Configuration sprawl that slows every release

Thousands of flags and rules nobody can safely delete, so the safe move is always to add one more.

done

Audited them across four repositories and shipped the audit as a production agent with canary verified gates and a no writes on uncertainty policy, plus eight more skills for staleness and owner routing. Dry runs caught three design defects before install.

Alerting nobody trusts any more

So real incidents arrive in a channel everyone has muted.

done

Cut automated notification noise about 330x, justified against a thousand recorded production runs rather than a sample, and it survived a 79 minute scheduler delay that would have broken the design I rejected.

An AI feature with no owner for the plumbing

The demo works. The pipeline behind it has no retries, no typed boundaries, no idea what it costs.

done

Built one end to end: async FastAPI and Celery over Postgres with pgvector, multi provider LLM routing, scheduled re-scrapes, error tracking. It replaced a four week manual process and runs a book in two to eight seconds.

The common shape: reversible change under production risk. Reduce the scary thing to a plan someone else can verify, then land it quietly.

reach me

Resume, one page, PDF

Every number on this page is one I can walk you through in an interview. Ask me about any of them. And this page is itself a sample: hand written HTML, CSS and a few lines of JS; no framework, no template, no tracker; subset self hosted fonts; every diagram drawn by hand.