Senior Blockchain Engineer

We've been building digital products for over 10 years, with a strong focus on Blockchain-based applications. At 4soft, people come first - it's our team of passionate technologists that enables us to work with international clients and deliver innovative solutions. We believe in transparency, effective teamwork, and achieving real business outcomes for those we serve.

As a Senior Blockchain Engineer, you’ll work directly with the client’s team as a dedicated engineer throughout the project. If you have experience building production financial infrastructure and care about the security of digital asset operations, this is your place.

Tech environment: MPC / custodial wallet platforms (Fireblocks, DFNS or similar), API integrations, stablecoins, DeFi (vaults), Web3

As a Senior Blockchain Engineer, you will be responsible for

• Helping scope a pilot that may initially include manual steps, and designing a path toward automation
• Building solutions on top of an MPC custody platform: lender and borrower accounts, collections wallets, transfers, and sweeps
• Defining transaction policies and pre-execution checks, including tight controls on permitted destinations
• Integrating outputs from an external calculation agent, or from internal calculations, without making smart contracts the primary money movement layer
• Designing and implementing automated wallet operations (deposit flows, sweeps, transfers) with a strong focus on security and auditability
• Collaborating with the client’s team, product, and business stakeholders to build solutions that fit real needs
• Taking shared ownership of the system from design through deployment and ongoing support

What we expect from you

• Hands-on experience building secure money movement solutions on MPC or custodial infrastructure (e.g. Fireblocks, Fordefi), primarily via API
• Experience with signing policies, transaction authorization, and wallet controls
• Experience with transaction automation and exchange-style flows: deposit and sweep flows
• Knowledge of DeFi sufficient to design integrations with confidence (deep smart contract expertise is not required)
• Experience building production financial infrastructure that critical business processes depend on
• Strong software engineering fundamentals: you write clean, testable code and think about maintainability and security
• The judgement to navigate trade-offs between security, speed of delivery, automation, and cost, and to communicate those decisions clearly to technical and non-technical stakeholders
• English proficiency at C1 level or above (for international client collaboration)
• Polish language skills at B2 level or above (for smooth communication with the team)

Great if you also bring

• Familiarity with credit facility models, stablecoins, and vault integrations
• Experience designing custody architecture and permission models (roles, limits, whitelisting, multi-approval)
• Experience with security infrastructure: key management, auditing, transaction monitoring
• Smart contract development experience (Solidity) as an additional asset

What helps us stay balanced

• Grow your skills and hobbies with us - make use of a dedicated training and wellbeing budget
• Work from home or the office - your choice, up to 100% remote
• Access to specialists whenever you need them via our LuxMed healthcare package
• If the gym is your second home, activate a Multisport card with us
• Looking for a long-term home? You're in the right place - stable collaboration, no dress code, no heavy atmosphere
• Our team knows how to have fun: board games, city outings, go-kart races, laser tag, great food on team retreats - we take integration seriously (in the best way :)