Full-Stack Software Engineering Intern (Winter 2026) at Sixtyfour (X25)

Sixtyfour builds advanced AI research agents to discover, link, and reason over comprehensive data about people and companies, transforming this intelligence into automated research workflows for sales, recruiting, and marketing. As a Full-Stack Software Engineering Intern, you will be instrumental in building polished, fast product experiences using Next.js + TypeScript, designing clean backend APIs with FastAPI/Python, and evolving our workflow engine. You will also ship robust data pipelines, deploy the stack on AWS + Docker, and implement product features end-to-end, ensuring high reliability, performance, and an excellent user experience.

Must Have

• Strong backend skills in Python (FastAPI preferred): API design, testing, error handling, schema/versioning.
• Good design taste.
• Experience deploying/operating with Docker and a major cloud (AWS preferred: ECS/EKS/Lambda, SQS, CloudWatch).
• Comfortable with Postgres (or MySQL) schema design and Redis (caching, rate limiting, locks).
• Performance mindset: RSC/Server Actions, data-fetching patterns, bundle/TTFB tuning, DB query perf.
• Production observability: logs, traces, metrics (e.g., Langfuse, OpenTelemetry, Sentry), and on-call pragmatism.
• Solid security hygiene (PII handling, secrets, JWT/session auth, CSRF/CORS, least-privilege access).
• Ability to commit to being in-person for the internship in San Francisco throughout winter (12 weeks), starting in December.

Good to Have

• Next.js App Router, RSC, Server Actions, edge/runtime primitives (Vercel/AWS CloudFront).
• Prisma/Drizzle; tRPC or GraphQL; Zod/JSON schema; feature flags/experimentation.
• Realtime UX (WebSockets/SSE), optimistic updates, background revalidation.
• Celery/RQ, event sourcing, or state-machine libs (e.g., Temporal, Dagster, Prefect, XState).
• Testing: Playwright (e2e), Vitest/Jest, pytest; accessibility checks.

About Sixtyfour

We build AI research agents that can discover, link, and reason over everything about people and companies. The platform turns that intelligence into automated research workflows for sales, recruiting, and marketing.

Sixtyfour is a data orchestration engine for company and people data. Our AI agents specialize in enriching detailed datapoints about individuals and organizations, gathering information from both public and proprietary sources. We enable enterprise customers to build custom data pipelines that help them find, enrich, qualify, and act on company-specific requirements for people and business data.

Our Mission

To power how enterprises understand and act on people and companies with world-class intelligence.

What you’ll do

• Build polished, fast product experiences in Next.js + TypeScript (design-quality UI, accessible components, responsive layouts).
• Design clean backend contracts and APIs (FastAPI/Python) for workflows, jobs, billing, and auth.
• Evolve our workflow engine (DAG/state machine): scheduling, retries/idempotency, rate limits, progress tracking, logs, and user-visible run history.
• Ship data pipelines and background workers (Celery/queues), with strong observability and alerting.
• Deploy the stack on AWS + Docker (ECS/EKS or similar), with caching (Redis), pagination, backpressure, and cost controls.
• Implement product features end-to-end: DB schema → API → UI, including tests and telemetry.
• Maintain a high bar for reliability, performance, and UX; instrument everything.
• Be very customer-focused on how certain product decisions impact end customers.

Minimum requirements

• Strong backend skills in Python (FastAPI preferred): API design, testing, error handling, schema/versioning.
• Good design taste is a must.
• Experience deploying/operating with Docker and a major cloud (AWS preferred: ECS/EKS/Lambda, SQS, CloudWatch).
• Comfortable with Postgres (or MySQL) schema design and Redis (caching, rate limiting, locks).
• Performance mindset: RSC/Server Actions, data-fetching patterns, bundle/TTFB tuning, DB query perf.
• Production observability: logs, traces, metrics (e.g., Langfuse, OpenTelemetry, Sentry), and on-call pragmatism.
• Solid security hygiene (PII handling, secrets, JWT/session auth, CSRF/CORS, least-privilege access).
• Be able to commit to being in-person for the internship in our San Francisco office throughout winter (12 weeks), starting in December

Nice to have

• Next.js App Router, RSC, Server Actions, edge/runtime primitives (Vercel/AWS CloudFront).
• Prisma/Drizzle; tRPC or GraphQL; Zod/JSON schema; feature flags/experimentation.
• Realtime UX (WebSockets/SSE), optimistic updates, background revalidation.
• Celery/RQ, event sourcing, or state-machine libs (e.g., Temporal, Dagster, Prefect, XState).
• Testing: Playwright (e2e), Vitest/Jest, pytest; accessibility checks.

Technology

Language Models, Opensearch/Elasticsearch, Next.js (typescript), Python, FastAPI, AWS, Docker, Celery workers, Playwright, Supabase, Stripe