Senior Backend Engineer (Req English)

3thix

Remote-First (Global) | Full-Time

About 3thix

3thix is a next-generation fintech platform bridging traditional payments with blockchain rails. We power seamless, low-cost, and compliant transfers using stable tokens, smart contracts, and hybrid on / off-ramp infrastructure. Backed by top-tier VCs, we process millions in daily volume and are expanding into new corridors and asset classes.

The Role

We’re hiring a Senior Backend Engineer with deep expertise in fintech payment systems, blockchain protocols, and stable token ecosystems (USDC, USDT, EURC, etc.). You’ll design, build, and scale the core transaction engine that routes fiat ↔ crypto, settles on-chain, and ensures regulatory compliance at every step.

What You’ll Do

Architect and maintain high-throughput payment orchestration services handling fiat deposits, crypto swaps, stable token mint / burn, and instant settlements.

Build reconciliation systems that sync on-chain events (EVM, Solana, Stellar) with off-chain ledgers and banking rails (ACH, SEPA, SWIFT, SPEI).

Implement risk, fraud, and AML controls in real-time transaction pipelines.

Design idempotent, event-driven microservices using Kafka / Pulsar and domain-driven patterns.

Own blockchain node infrastructure (Geth, Solana RPC, custom indexers) and write secure smart-contract interaction layers.

Scale systems to 10k+ TPS with sub-100ms latency for cross-border flows.

Collaborate with compliance and product teams to embed KYC / KYT, travel-rule data, and sanction screening.

Lead incident response for payment disputes, rollbacks, and chain re-orgs.

Must-Have Skills

5+ years backend engineering in high-scale environments.

Production experience in fintech / payments (acquiring, issuing, remittance, or payout systems).

Deep blockchain knowledge :

EVM-compatible chains (Ethereum, Polygon, Arbitrum)

Stable token standards (ERC-20, SPL, CCTP)

MEV, gas optimization, and on-chain data indexing (The Graph, Dune, custom subsql)

Mastery of Go, Rust, or TypeScript / Node.js (we primarily use Go).

Event sourcing, CQRS, and distributed transaction patterns.

Secure handling of HSMs, key management (KMS, MPC), and cryptographic signing.

Observability stack : Prometheus, Grafana, OpenTelemetry, ELK.

Experience with regulated environments (PCI-DSS, SOC2, PSD2, FinCEN travel rule).

Nice-to-Have

Built or audited stablecoin issuance / redemption systems.

Contributed to open-source blockchain tooling or payment protocols.

Worked with layer-2 networks (Optimism, Base, zkSync) or cross-chain bridges.

Familiarity with ISO 20022, FedNow, or RTP rails.

Tech Stack

Core : Go, Rust, PostgreSQL, Redis, Kafka

Blockchain : Solidity, Hardhat, Foundry, ethers.js, viem, Solana SDK

Infra : Kubernetes, Terraform, GCP / AWS, Grafana Tempo

Security : HashiCorp Vault, AWS KMS, Fireblocks MPC

Why Join 3thix

Equity in a rocket-ship startup.

Unlimited PTO + global off-sites.

Top-tier health, dental, and remote workspace stipend.

Work directly with ex-Stripe, Circle, and Coinbase engineers.

Shape the future of programmable money.