The Vault is an MPC-based crypto custody platform for institutional and retail clients, running threshold signing across HSM and Ledger hardware. We're scaling toward Series A, launching our productized platform in 2026, and publishing original cryptographic research alongside the product.
We're hiring a Staff Engineer to design and ship the custody platform's hardest backend code. This is a hands-on IC role with real technical leadership — no people management — where you drive non-trivial initiatives through code, RFCs, and mentorship.
You'll shape architecture in your area of ownership; We're AI-forward (Claude Code, Cursor, Codex), and we need engineers who can read AI-generated code critically and catch what it misses — not just prompt it.
You'll naturally gravitate toward either the security-critical core (MPC, threshold signing, HSM/Ledger integration, key lifecycle) or the faster-moving periphery (chain adapters, integrations, APIs/SDKs).
Build high-load, multi-tenant SaaS systems: tenant isolation, quotas, rate limits, backpressure, concurrency control, predictable latency under spikes.
Security-by-design: least privilege, secret handling, mTLS/JWT, tamper-evident logs, audit-ready data models — designed for SOC 2, ISO 27001, and DORA scope from day one.
Performance & data: profiling, load testing, benchmarking, contention analysis, GC tuning; contribute to the company's AI engineering practices; know when to use AI heavily (periphery, integrations, tests, docs) and when not to (cryptographic core, signing paths)



where blind generation is unsafe.
Set patterns and shared libraries for the services your area touches; raise the bar through code review and example.
Own features end-to-end: design notes / RFCs, code, tests, observability, rollout, on-call. No "throw it over the wall" handoffs.
Mentor senior engineers: your reviews and your written designs are the strongest signal to the rest of the team.
You can reason from first principles about concurrency, distributed systems, consistency models, networking, and OS behaviour. 10+ years backend engineering, including 3+ years operating at Staff level (or equivalent senior IC scope). Strong production experience in a modern systems language — Go, Rust, Java, C++, or comparable. Hands-on with modern backend stacks: gRPC/ queues/streams, caching, relational databases, Kafka/NATS or equivalent.

- Strong testing discipline: unit/integration/contract tests, testability-first design, deterministic CI.
- REQUIRED: production-grade use of modern AI coding tools (Claude Code, Cursor, Codex, or comparable). Multiple blockchain ecosystems (EVM and Bitcoin minimum; Kubernetes and service mesh in production; An AI-forward engineering culture with budget and autonomy for the tooling, models, and agents you need.

Direct peers in cryptography research, security architecture, product, and delivery — you're not the only senior voice in the room.
Fully remote, any time zone with reasonable overlap with EU/CIS hours.

📌 Senior Staff Backend Engineer (Barcelona)
🏢 The Vault
📍 Barcelona