Jakub Kozłowski
Lead Software Engineer (contract) at SiriusXM
Wrocław, Lower Silesian Voivodeship, Poland
Summary
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Rockstar🎓
Top SchoolJakub Kozłowski is a Lead Software Engineer with 12 years of experience building robust, API-first tooling and backend systems, currently leading engineering efforts at SiriusXM from Wrocław. He specializes in Scala and functional programming, contributing to high-profile open-source projects like Metals, Cats, Cats-Effect, fs2 and http4s where he focused on refactors, performance fixes and developer ergonomics. Jakub blends hands-on implementation with technical leadership—designing experiments, proposing API designs in Smithy, and mentoring teams while owning delivery and risk mitigation. His background spans streaming and subscription platforms at Disney Streaming, complex warehouse systems at Ocado, and end-to-end consulting work, showing strong domain versatility. He also does DevOps and build engineering (Nix, Docker) and routinely improves build stability and dependency management across projects. Outside of work he speaks at conferences and balances deep technical craft with practical tools that improve other engineers’ productivity.
12 years of coding experience
8 years of employment as a software developer
Computer Science, Computer Science at Warsaw University of TechnologyMathematics, Mathematics at University of Warsaw
English, German, Polish
Stackoverflow
493reputation
36kreached
11answers
4questions
Github Skills (72)
dependency-management10
concurrent-programming10
package-management10
nix10
dependency-analysis10
testing10
http10
code-completion10
language-server-protocol10
type-system10
effects10
f10
build-automation10
maven10
stream-processing10
Programming languages (28)
Github contributions (5)
typelevel/cats-effect
Jul 2018 - Jul 2021
The pure asynchronous runtime for Scala
Role in this project:
Back-end Developer
Back-end DeveloperContributions:104 reviews, 183 commits, 53 PRs in 3 years 1 month
Contributions summary:Jakub primarily focused on refactoring and enhancing the `cats-effect` library. They made significant code changes, renaming methods and adjusting types within the core concurrent and playground modules. Further contributions included fixing compilation issues in test files and improving the `racePair` functionality by extracting common code. The user's work involved deep modifications within the concurrent and testing areas of the project.
asynchronousfunctional-programmingcontinuationtypeclassesruntime
cb372/scalacache
Feb 2020 - Feb 2022
Simple caching in Scala
Role in this project:Back-end Developer
Back-end DeveloperContributions:13 reviews, 38 commits, 11 PRs in 2 years
Contributions summary:Jakub primarily focused on improving the `scalacache` library. They made changes to caching logic, introducing performance optimizations by modifying how the TTL is handled. Additionally, they updated the project's dependencies, specifically upgrading the `cats-effect` library, and ported a Caffeine module, demonstrating a focus on library maintenance and enhancement. Further changes involved refactoring code and removing dependencies.
cachingscala3scalacachedotty
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