Senior Software Engineer Startup Jobs in California

New York, NY or San Francisco, CA · On-site (5 days/week) · Full-time Compensation: $180,000 to $280,000 + equity

Our client is a venture-backed startup building enterprise-grade AI agents that automate high-stakes contract and document workflows for some of the world's largest companies. The founding team recently joined a major enterprise-software organization through an acquisition, so you get the ownership and pace of an early-stage team with the distribution and resources of a much larger business behind it. Leadership has deliberately kept the group operating in high-velocity startup mode, with its own engineering, product, and go-to-market functions. This is a small, founder-led team with real influence over the product.

Early-stage, founder-led team · venture-backed and recently acquired · Industry: AI, Enterprise Software, Legal Tech

We are hiring a Senior Software Engineer to own AI and agentic backend and infrastructure work end to end, reporting directly to the founders. The work is greenfield: you will architect core systems from scratch and own the security-critical pieces that enterprise customers depend on, including SOC 2 controls, encryption and key management, customer-held encryption keys (BYOK), and the infrastructure that AI agents run on. There is meaningful cloud infrastructure and DevOps work alongside the backend build.

What you'll be doing

• Architect and build core features from scratch with a focus on reliability, scalability, and security.
• Own security requirements: SOC 2 controls, encryption and key management, access controls, and customer BYOK.
• Design and secure the infrastructure that AI agents run on, and build and deploy AI-powered agents in Python.
• Build robust agent workflows that integrate LLMs, APIs, databases, business systems, and external tools.
• Stand up and scale cloud infrastructure (AWS or Azure), including a meaningful DevOps component.
• Establish engineering best practices, tooling, and culture as an early member of a small, high-impact team.

Tech stack: Python (ML and agentic infrastructure), AWS or Azure with DevOps, JavaScript/TypeScript, LLM-powered agents, agent orchestration and MCP.

• 5+ years building and shipping production backend systems.
• A track record of shipping production systems in a startup or other high-ownership environment.
• Time spent at a small startup (under 100 people) as a founder, founding engineer, or early hire.
• Experience designing or implementing security-sensitive systems such as encryption, key management, and authentication.
• Hands-on experience building or deploying AI/ML or LLM-powered agents in production.
• Strong, production-grade Python for ML and agentic infrastructure.
• Cloud infrastructure experience with AWS or Azure, including DevOps.
• Production experience with JavaScript or TypeScript.
• Ability to build agentic systems end to end and reason about agent orchestration and MCP at a systems-design level.
• High agency: you self-direct, identify problems, and solve them independently.
• Comfort translating ambiguous enterprise security requirements into concrete systems.
• Willing to work on-site 5 days per week in New York or San Francisco.

• Experience at a larger, established technology company alongside your startup chapters, for balance.
• Background building or securing systems in a regulated domain (for example fintech or health tech).

• Report directly to the founders with a real seat at the table and no layers of management.
• Greenfield ownership: architect and build core systems from scratch with full control over technical decisions.
• Security and AI agent work that genuinely matters, shipped for some of the world's largest enterprises.
• Startup energy and ownership paired with enterprise-scale distribution and resources.
• A wide-open market at an inflection point, with a team carrying deep AI and commercial-contracting experience.

• Location: New York, NY or San Francisco, CA
• Work policy: On-site, 5 days per week
• Compensation: $180,000 to $280,000 plus equity
• Visa sponsorship: Open to relocation and to transferring existing US work visas (for example H-1B or OPT transfers); new visa sponsorship is not available.
• Employment type: Full-time