Top Principal Software Engineer Jobs in San Francisco, CA

Lead architectural evolution of a high-traffic B2B SaaS supplier platform: define microservice boundaries, APIs, CI/CD, multi-cloud deployment, security, multi-tenancy, and mentor engineers while partnering with SRE, product, and business teams.

As a Senior Principal Engineer, you'll define and drive the technical strategy for customer experience platforms, lead architectural decisions, and mentor engineering teams to enhance customer and agent experiences.

Design, build, deploy, and maintain resilient, scalable production systems for Toast’s retail customers. The role sets long-term technical architecture and strategy, communicates technical direction, mentors senior engineers, improves engineering productivity, diagnoses performance issues, and drives initiatives amid ambiguity. Engineers collaborate directly with retail customers, visit stores, understand operational workflows, and use AI tools to improve development velocity and quality.

Design, build, and operate secure, resilient distributed systems for secrets and key management across Cloudflare's global network. Re-architect and strengthen internal PKI and machine/workload identity, support and run services (including on-call), and consult with teams to ensure secure system design and usage.

This role involves leading technical projects across multiple teams, designing scalable systems, collaborating with cross-functional teams, and mentoring engineers, focusing on payroll and tax systems at Gusto.

Own the multi-year strategy and technical direction for Lambda’s large-scale networking software across GPU fabrics, cloud networks, backbone, and edge infrastructure. Lead architecture, design, implementation, operations, customer engagements, and cross-functional delivery of distributed network services. Mentor engineers, resolve complex technical issues, participate in on-call operations, and guide mission-critical enterprise projects while improving system performance, availability, scalability, and cost.

Own the multi-year networking software strategy for Lambda’s large-scale AI cloud. Set technical standards, lead architecture and delivery of distributed network services, guide enterprise customers, resolve cross-team technical challenges, and remain hands-on with complex systems. Mentor engineers, participate in hiring and design reviews, operate production services through on-call rotations, and identify improvements to network availability, performance, and customer products.

Build, scale, and operate production-grade machine learning systems powering real-time personalization. Lead cross-functional ML initiatives, develop and validate models, create scalable data-analysis processes, prevent regressions through testing, and improve system quality. Partner with Product and Engineering while providing technical leadership in a fast-paced startup environment.

Lead architecture and technical execution for Toast’s Payroll and Team Management products. Own authentication, authorization, and organizational hierarchy across a multi-tenant SaaS platform. Drive high-scale, full-stack initiatives, modern agentic development practices, integrations, technical strategy, quality standards, deployment practices, and cross-functional collaboration. Mentor engineers across teams and leverage AI tools and LLM integration to improve software development velocity and quality.

Lead the technical direction, architecture, governance, and standards for a backend platform serving multiple engineering teams. Develop AI-native workflows, resolve cross-cutting distributed-systems challenges, influence roadmaps, drive platform adoption, mentor senior engineers, lead complex initiatives, and participate in on-call rotations. The role requires broad expertise across cloud infrastructure, Terraform, CI/CD, GraphQL federation, event-driven systems, APIs, developer experience, Node.js, and TypeScript.

Own the architecture of Plug’s money-facing infrastructure, including ledgers, payment disbursements, settlements, reconciliation, and lien/title payoffs. Design deterministic, auditable, fault-tolerant financial systems that integrate with banks, processors, and servicers while meeting regulatory requirements. Partner with Product, Risk, Finance, and Compliance, establish technical standards, review money-related architecture, mentor engineers, and guide build-versus-buy decisions.

Design and build large-scale, highly available Responsible AI cloud services. Lead architecture, development, release, and production readiness. Collaborate with engineers, scientists, and product managers to integrate Responsible AI features across Azure AI and related services, drive DevOps practices, and improve performance, observability, and reliability.

Own the architecture and technical direction of large-scale distributed systems or agent-centric AI products. Lead complex technical decisions, establish engineering standards, partner with executive leadership, and guide high-priority initiatives. Build and operate production systems serving over 100,000 users while using AI-assisted development tools. The role requires extensive backend or full-stack engineering experience and offers Staff or Principal-level scope.

Lead backend architecture and deliver reusable solutions, unblock engineering teams across the development lifecycle, drive complex design and bug fixes, set code review standards, mentor engineers, collaborate on company-wide projects, and make technical decisions balancing correctness, performance, and customer impact.

Design and operate large-scale, AI-native cloud infrastructure (especially Kubernetes/AKS). Improve service quality, automate incident prevention/remediation, accelerate engineering productivity, and integrate AI tools into development workflows.

Build and operate production-quality AI framework, runtime, benchmarking, performance, automation, observability, and developer-tooling systems. Optimize large language model training and inference across GPUs and Microsoft hardware, diagnose cross-stack reliability and performance issues, and improve model onboarding, hardware utilization, Azure efficiency, and deployment speed. Senior engineers own major components and projects; Principal engineers define technical direction, architecture, and multi-release strategy while leading cross-team initiatives and mentoring technical leaders.

Lead the design and development of scalable document-processing systems for healthcare workflows. Build Go services and AWS Step Functions pipelines, solve large-scale PDF processing challenges, implement observability, optimize PostgreSQL/RDS performance, and support OpenSearch indexing. Provide architectural direction, mentor engineers, translate ambiguous requirements into shipped solutions, and ensure reliable handling of sensitive PHI under HIPAA requirements.

Define technical direction for hyperscale Azure Storage components; architect, develop, test, and support highly scalable, secure, compliant, and highly available cloud services. Lead multiple engineering projects, improve reliability, scalability, performance, consistency, and observability, and apply AIOps for incident detection, root-cause analysis, and operational excellence.

The Principal Software Engineer will design and implement systems for the advertiser experiences at Snap, lead technical vision, mentor engineers, and innovate on creator marketplace products.

Lead technical ownership of a global platform for safe change: distributed key-value storage, progressive configuration delivery, testing and health-mediation. Write production code, design systems, review senior proposals, integrate LLMs, and drive cross-team initiatives to improve reliability, rollout safety, and developer productivity.

Lead architecture, design, and delivery of PET product features; write production full‑stack code; champion testing, observability, CI/CD and operational readiness; mentor engineers and collaborate with product to shape technical roadmap.

Lead the software architecture and development of a clinical prototype for precision surgery. Build robust multi-device communication infrastructure, high-performance data and image processing, real-time systems, and responsive desktop interfaces. Collaborate with hardware, research, mechanical, electrical, and clinical teams while balancing rapid prototyping with regulated medical software requirements. Mentor engineers, establish software processes, and guide development through first-in-human studies.

The Principal Software Engineer will design automated ad serving systems, lead technical direction, collaborate with teams, and mentor engineers.

Lead architecture and technical strategy for a unified telemetry and observability platform spanning endpoint collection SDKs to cloud ingestion and analytics. Design high-performance, resource-constrained, crash-survivable telemetry systems across Windows, macOS, and Linux; drive data governance, privacy/PII handling, and backward-compatible platform evolution. Mentor and lead distributed engineering teams.

Develop and operate production AI framework components, runtimes, benchmarking systems, performance tools, and integrations. Benchmark and optimize large language model training and inference across GPUs and Microsoft hardware, build automation and observability, investigate cross-stack performance and reliability issues, and deliver scalable platform improvements. Principal engineers additionally set technical direction, lead multi-team initiatives, define architectures, and mentor technical leaders.