Application Security Engineer

Braintrust•Seattle, WA

About The Position

We're looking for an Application Security Engineer who lives in the code. Braintrust is a real-time, high-availability data platform that runs in both SaaS and self-hosted environments, with open source libraries embedded inside thousands of customer applications and a model proxy in front of OpenAI, Anthropic, Gemini, and other major model providers. This is a hands-on IC role. You'll review code, build threat models, ship paved-road libraries, and lead AI-specific security work: prompt injection, agent sandbox escapes, tool-use abuse, and the new attack surface that comes with LLM-native applications. If you reach for agentic coding tools as your default workflow and can hold your own in a design review with a backend or systems engineer, we'd love to work with you.

Requirements

5+ years in application security, product security, or backend engineering with a security focus — you've shipped real code and reviewed a lot of it
Strong code reading and writing skills in at least two of TypeScript/Node.js, Python, Go, or Rust
Deep knowledge of common web and API vulnerability classes and the architectural patterns that prevent them — not just OWASP Top 10 trivia
Track record of building secure-by-default libraries, frameworks, or services that other engineers actually adopt
Hands-on experience with authn/authz design, multi-tenant data isolation, and secrets/key management at scale
Comfortable with the realities of a high-availability data platform: real-time pipelines, ingestion at scale, semi-structured data, Postgres, Redis, AWS
A clear point of view on AI/LLM security — prompt injection, agent abuse, tool-use sandboxing, model proxy threats — and ideally hands-on experience defending against them
Daily user of agentic coding tools and excited to push the frontier of how AppSec gets done with them
Clear communicator who documents decisions, writes tickets engineers want to pick up, and lifts the team's security awareness without becoming a bottleneck

Nice To Haves

Prior experience with LLM red-teaming, agent sandbox research, or shipping security-focused open source libraries

Responsibilities

Drive secure design across the platform: lead threat models for new features, review architecture proposals, and partner with product and backend engineers to ship features that are secure by default
Review code across our TypeScript, Python, and Go services, our open source tracing libraries, and our model proxy — and find the bugs others miss
Build the paved road: authn/authz primitives, RBAC and tenancy isolation patterns, secret handling, safe data pipelines, and sandboxed code execution for user-supplied JavaScript and Python snippets
Own our SAST, DAST, SCA, and secret-scanning tooling end-to-end, keeping signal-to-noise high enough that engineers actually fix what you ship
Run our vulnerability management program and triage external bug bounty reports; close the loop with durable fixes, not point patches
Lead AI-specific security work: prompt injection defenses, model proxy abuse detection, agent and tool-use sandboxing, data-exfiltration controls in multimodal pipelines, and security for the eval workflows our customers run
Partner with our open source maintainers on the security of libraries that get embedded inside customer applications
Use agentic coding workflows to scale yourself: automated code review, exploit prototyping, control validation, and IR triage