Software Engineer, Payments Infrastructure

Sierra•San Francisco, CA

3d•$230,000 - $390,000•Onsite

About The Position

Sierra is hiring a Software Engineer for its Payments Infrastructure work. The role spans payments, security, real-time voice, and LLMs. It focuses on securely collecting and using card details during live calls while ensuring plaintext card numbers never reach the model. Sierra owns the systems that touch card data, and a small team manages the platform end to end across Platform, Product, and Safety & Integrity. Payments is in production for large consumer enterprises on a PCI DSS Level 1-certified platform handling hundreds of millions of calls annually. The engineer will build and extend real-time card capture and tokenization, control approved destinations for card data, ensure payment actions are correct, and prevent card data from reaching inappropriate systems. The role also includes making payments self-service across Sierra's agent-building products and extending tokenization into a privacy vault for other personally identifiable information. Customers retain their own telephony and payment gateways. Sierra is primarily an in-person company based in San Francisco, with offices across North America, Europe, and Asia. Its stated values are Trust, Customer Obsession, Craftsmanship, Intensity, and Family.

Requirements

At least 5 years building backend, platform, or infrastructure systems.
Track record of shipping and operating high-reliability production services.
Strong security instincts, including reasoning about compromise, blast radius, least privilege, and preventing unsafe states.
Rigor around correctness under failure, including retries, idempotency, at-most-once behavior, timeouts, and ambiguous results from external systems.
Fluency in a systems language; Sierra uses Go.
Comfort owning critical systems end to end, from design through production and on-call.
Ability to build clean abstractions over complex external systems and take ownership in a small team with broad scope.
Clear communication of designs and risks to engineering teams and non-engineers.
Degree in Computer Science or a related field, or equivalent professional experience.

Nice To Haves

Experience with real-time or streaming systems such as voice, telephony, media, or low-latency pipelines.
Experience with applied cryptography and key management, network isolation, egress control, or cloud security.
Experience building platforms other engineering teams use, such as APIs, SDKs, and self-service developer services.
Experience with deployments into customer-owned clouds or single-tenant environments.
Customer-facing technical experience, such as architecture reviews with customers.
Experience setting technical direction on ambiguous, high-stakes problems.
Experience in payments, fintech, or another sensitive-data domain such as healthcare or identity.

Responsibilities

Build real-time card capture for voice by intercepting keypad and spoken digits in live audio upstream of the agent runtime, in a network-segmented environment, while keeping the LLM on the call.
Support card capture across every telephony provider and protocol Sierra supports.
Build and extend tokenization so agents use short-lived tokens and the platform exchanges tokens for real values only when calling a customer's payment gateway.
Own the payments egress control plane, ensuring every card-data destination is approved, versioned with the agent release, and enforced by infrastructure below the application.
Build correct payment actions, including an at-most-once action primitive in the Agent SDK, validation of amounts and items, and monitoring that compares what the agent said about a payment with what occurred.
Implement deterministic detection in the agent's hot path to keep card data out of inappropriate systems and ensure no LLM sees a plaintext card number.
Make payments self-service through a shared API across Agent Studio, the Agent SDK, and Ghostwriter; gateway middleware developers can use with tokens; and support for single-tenant and customer-cloud deployments.
Extend tokenization beyond cards into a privacy vault for all personally identifiable information.
Own critical systems end to end, from design through production and on-call.

Benefits

Flexible (unlimited) paid time off.
Medical, dental, and vision benefits for employees and their families.
Life insurance and disability benefits.
Retirement plan dependent on country of employment.
Parental leave.
Fertility and family-building benefits through Carrot.
Lunch, snacks, and coffee.
Discretionary benefit stipend.
Free alphorn lessons.
Eligible full-time employees can participate in Sierra's equity plans, subject to applicable plans and policies.