Security engineer, application security (UK)

🚀 About WRITER: Revolutionizing Enterprise AI
At WRITER, we're not just building software; we're expanding human capacity through superintelligence. We empower the world's leading enterprises to orchestrate AI-powered work, uniting IT and business teams to unlock enterprise-wide transformation with powerful, trustworthy AI. Our end-to-end platform enables hundreds of companies like Mars, Marriott, Uber, and Vanguard to build and deploy AI agents grounded in their proprietary data and fueled by WRITER's enterprise-grade LLMs.
Valued at $1.9B and backed by industry giants including Premji Invest, Radical Ventures, and ICONIQ Growth, WRITER is rapidly cementing its position as the leader in enterprise generative AI. Founded in 2020 with hubs in San Francisco, New York City, Austin, Chicago, and London, our team thinks big and moves fast. If you're a smart, hardworking builder and scaler ready to shape the future of work with AI, we want you to join our journey.

📐 The Mission: Secure the Future of Enterprise AI as an Application Security Engineer
This is where cutting-edge security meets boundless innovation at enterprise scale. As an **Application Security Engineer** at WRITER, you will be a foundational architect of trust, building the robust security infrastructure that protects the AI systems powering some of the world's most recognizable brands. You'll operate at the thrilling intersection of application security, advanced AI infrastructure, and developer enablement – a unique opportunity to embed security into every line of code, ensuring our platform remains both powerful and absolutely trustworthy.
The scope of this opportunity is immense: you will actively define how enterprise AI applications are secured from the ground up. Imagine threat modeling sophisticated LLM architectures, building automated security controls that seamlessly scale across our rapidly expanding platform, and pioneering defenses for systems that literally didn't exist just a few years ago. This isn't about rigid enforcement; it's about finding creative, ingenious ways to enable innovation securely. You'll tackle unprecedented challenges: securing AI agents, fortifying critical training data pipelines, and designing controls for a new era of technology.
This role offers flexibility, allowing you to work remotely within the US or hybrid from our San Francisco or New York City offices. You will report directly to the Head of Security Engineering, making a direct impact on our strategic security posture.

🦸🏻‍♀️ What You'll Be Building & Protecting:

**Security by Design:** Embed security into the very DNA of our AI platform. You'll lead threat modeling sessions with product teams, design secure architectures for new features, and ensure security considerations are integral to product decisions from day one.
**Evolve AppSec Program:** Own and continuously enhance our application security program. This includes establishing and maintaining SAST/DAST scanning within CI/CD pipelines, conducting rigorous security code reviews for critical changes, and building automation that proactively identifies and remediates vulnerabilities before they ever reach production.
**Developer Empowerment:** Partner closely with engineering teams to champion and establish secure coding standards. You'll create reusable security patterns and libraries that empower developers to build securely by default, reducing friction and increasing velocity.
**Customer Advocate & Visionary:** Design and recommend security features and products that enhance the security of our customer environments. You will be the unequivocal advocate and visionary for how we protect and secure our customers' valuable data and AI agents.
**AI for Security:** Integrate and leverage AI agents to significantly increase the velocity of the security team and the broader engineering organization, ensuring we are proactive in minimizing risk as we innovate.
**Proactive Defense:** Lead comprehensive security assessments and penetration testing of WRITER's applications, AI services, and APIs. You'll identify vulnerabilities across our entire tech stack and collaborate with teams to remediate issues at scale.
**Pioneering Controls:** Design and implement robust security controls specifically tailored for protecting data pipelines, sensitive model training environments, and customer-facing AI agents – addressing novel security landscapes.
**Threat Intelligence:** Stay relentlessly ahead of emerging threats in the AI/ML security landscape. This includes deep research into attack vectors specific to LLMs and generative AI, proactively building robust defenses against novel risks.

⭐️ What You'll Bring to the Table:

**Proven AppSec Expertise:** 2+ years of hands-on experience in application security engineering, with a strong track record of securing large-scale production systems. Bonus points for experience in fast-growing startups or high-growth environments.
**Developer Empathy:** A profound understanding of developer experience and workflows for shipping features and products. You care deeply about reducing risk while simultaneously optimizing engineering velocity.
**Technical Fluency:** Expertise in at least two programming languages (e.g., Python, Java, Go, JavaScript/TypeScript) and the ability to confidently read and review code across multiple languages, discerning both business logic and critical security implications.
**DevSecOps Mastery:** In-depth knowledge of modern security tools and methodologies, including SAST/DAST solutions, vulnerability management platforms, security testing frameworks, and advanced DevSecOps practices. You instinctively know which tools to wield and when automation is superior to manual review.
**Impactful Communication:** Exceptional communication skills that allow you to translate complex security concepts into clear, actionable recommendations for both highly technical and non-technical audiences. You can articulate not just the 'what,' but the 'why,' motivating teams to decisive action.
**Builder's Mindset:** A proactive, "builder's" approach that constantly seeks opportunities to automate, scale, and empower, rather than create bottlenecks. You understand that security is a critical enabler of the business, not a blocker.
**Values Alignment:** A strong alignment with WRITER's core values:

**Connect:** Building strong, collaborative relationships across diverse teams.
**Challenge:** Pushing the boundaries of what's possible in AI security.
**Own:** Taking end-to-end responsibility for the security posture of our platform.

🍩 Benefits & Perks (UK full-time employees):

Generous PTO, plus company holidays
Comprehensive medical and dental insurance
Paid parental leave for all parents (12 weeks)
Fertility and family planning support
Early-detection cancer testing through Galleri
Competitive pension scheme and company contribution
Annual work-life stipends for:

Wellness stipend for gym, massage/chiropractor, personal training, etc.
Learning and development stipend

Company-wide off-sites and team off-sites
Competitive compensation and company stock options