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Sierra is a leading platform for customer-facing AI agents serving major brands including The GAP, Rocket Mortgage, SoFi, Sutter Health, and SoftBank. The company is headquartered in San Francisco with offices across North America, Europe, and Asia. Co-founders include Bret Taylor (former Salesforce co-CEO, Google Maps co-creator, current OpenAI Board Chair) and Clay Bavor (18-year Google veteran who led Google Labs and AR/VR initiatives).
In this role, you will own the payments infrastructure that enables AI agents to securely handle payment card data without exposing sensitive information to the LLM. The core technical challenge involves building real-time card capture for voice interactions—intercepting keypad and spoken digits in live audio streams while keeping the model on the call, all within a PCI DSS Level 1 certified platform handling hundreds of millions of calls annually.
Key responsibilities include:
- Build real-time card capture for voice: intercept keypad and spoken digits in live audio streams upstream of the agent runtime in a network-segmented environment, ensuring the LLM never sees plaintext card numbers. Support every telephony provider and protocol Sierra uses.
- Build and extend the tokenization platform: agents work with short-lived tokens; the platform swaps tokens for real values only when calling the customer's payment gateway.
- Own the payments egress control plane: ensure every destination for card data is approved, versioned with agent releases, and enforced by infrastructure below the application layer.
- Make payment actions correct: implement at-most-once action primitives in the Agent SDK with validated amounts and items; implement monitoring that compares agent statements about payments with actual outcomes.
- Keep card data secure: deploy deterministic detection in the agent's hot path to catch sensitive data that general-purpose models miss.
- Make payments self-serve: create a unified payments API across Agent Studio, the Agent SDK, and Ghostwriter (Sierra's agent-building agent); build gateway middleware for developers to work with tokens; support single-tenant and customer-cloud deployments.
- Grow the platform: extend tokenization into a privacy vault for all PII.
You will work on a small team with broad scope, owning systems end-to-end from design through production and on-call support. The role sits at the intersection of four hard technical domains: payments, security, real-time voice, and LLMs.
REQUIREMENTS:
- 5+ years building backend, platform, or infrastructure systems with a track record of shipping and operating high-reliability services in production
- Deep security instinct: design assuming every component will eventually be compromised; reason naturally about blast radius, least privilege, and making bad states impossible
- Rigor about correctness under failure: expertise with retries, idempotency, at-most-once behavior, and clear handling of timeouts and unclear results from external systems
- Fluency in a systems language (Go preferred) and comfort owning critical systems end-to-end from design through production and on-call
- Range and ownership: thrive in small teams with broad scope; build clean abstractions over messy external systems; solve problems once for all customers, not per-customer
- Clear communication: explain designs and risks to engineering teams and non-engineers
- Degree in Computer Science or related field, or equivalent professional experience
PREFERRED QUALIFICATIONS:
- Experience with real-time or streaming systems (voice, telephony, media, low-latency pipelines)
- Applied cryptography, key management, network isolation, egress control, or cloud security
- Platform work: APIs, SDKs, self-serve developer services
- Customer-owned cloud or single-tenant deployments
- Customer-facing technical work (architecture reviews)
- Setting technical direction on ambiguous, high-stakes problems
- Payments, fintech, or sensitive-data domains (healthcare, identity)
Note: Payments experience is not required. The platform was built by engineers from backend, infrastructure, and security backgrounds. Sierra values how you build correct, secure systems over domain-specific keywords.
