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Senior Fastapi Developer Jobs in Boston, MA (NOW HIRING)

Klaviyo

Senior AI Engineer - Customer Agent

Boston, MA · On-site

$113K - $155K/yr

Our team is looking for a Sr. AI Engineer on the Customer Agent team, Klaviyo's AI-native ... Proficient in Python and modern backend frameworks (FastAPI, Django preferred). * Experience ...

VIA

Senior Software Engineer, Cryptography

Somerville, MA · On-site

$150K - $200K/yr

You will collaborate with senior engineers and developers on VIA's Zero Trust Fabric: A product ... Experience developing RESTful APIs (e.g., FastAPI) secured by OAuth2/JWT * Experience integrating ...

VIA

Senior Software Engineer, Cryptography

Somerville, MA · On-site

$150K - $200K/yr

You will collaborate with senior engineers and developers on VIA's Zero Trust Fabric: A product ... Experience developing RESTful APIs (e.g., FastAPI) secured by OAuth2/JWT * Experience integrating ...

VIA

Senior Software Engineer

Somerville, MA · On-site

$133K - $176K/yr

An impressive mission requires an equally impressive Senior Software Engineer. As a key technical ... Developing RESTful APIs (using frameworks such as FastAPI) secured by OAuth2/Auth * Integrating ...

VIA

Senior Software Engineer

Somerville, MA · On-site

$133K - $176K/yr

An impressive mission requires an equally impressive Senior Software Engineer. As a key technical ... Developing RESTful APIs (using frameworks such as FastAPI) secured by OAuth2/Auth * Integrating ...

PathAI

Senior Software Engineer, Fullstack

Boston, MA · On-site

$127K - $195K/yr

... Senior Software Engineer to join our team. You will help solve interesting problems with code and ... You have demonstrated experience and skills in designing and building Python-based (FastAPI or ...

PathAI

Senior Software Engineer, Fullstack

Boston, MA · On-site +1

$127K - $195K/yr

... Senior Software Engineer to join our team. You will help solve interesting problems with code and ... You have demonstrated experience and skills in designing and building Python-based (FastAPI or ...

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How much do senior fastapi developer jobs pay per hour?

As of Sep 13, 2026, the average hourly pay for senior fastapi developer in Boston, MA is $67.06, according to ZipRecruiter salary data. Most workers in this role earn between $56.92 and $75.19 per hour, depending on experience, location, and employer.

What does a Senior FastAPI Developer do?

A Senior FastAPI Developer designs, develops, and maintains backend web applications using the FastAPI framework in Python. They are responsible for building scalable APIs, optimizing performance, ensuring security best practices, and integrating with databases and external services. Senior developers also mentor junior team members, contribute to architecture decisions, and collaborate closely with front-end engineers and stakeholders to deliver robust software solutions.

What are the key skills and qualifications needed to thrive as a Senior FastAPI Developer?

To thrive as a Senior FastAPI Developer, you need deep expertise in Python, RESTful API design, and experience building scalable web backends, typically supported by a degree in computer science or related field. Familiarity with FastAPI, Docker, cloud platforms (such as AWS or Azure), and CI/CD tools is highly valued, along with proficiency in testing frameworks. Strong problem-solving, leadership, and communication skills help you collaborate effectively with cross-functional teams and mentor junior developers. These skills enable the delivery of robust, efficient, and maintainable APIs that support business goals and high user demands.

What are some common challenges faced by Senior FastAPI Developers when scaling applications, and how can these be addressed?

Senior FastAPI Developers often encounter challenges related to managing high concurrency, optimizing API performance, and ensuring robust security as applications scale. To address these, it’s important to implement asynchronous programming practices, leverage efficient database queries, and utilize API gateways for better traffic management. Collaboration with DevOps and QA teams is also essential to automate deployments and monitor system health, ensuring smooth scaling and reliable user experiences.

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Senior AI Engineer - Customer Agent

Boston, MA • On-site

Klaviyo
Marketing • 1 - 5K employees
Learn more about Klaviyoexternal

$113K - $155K/yr

Full-time

Re-posted 9 days ago

Job description

About the Role

At Klaviyo, we believe the future of software lies not in productivity tools for human users but in software that can run and optimize itself based on outcome or reward metrics. We've built the infrastructure and application that serve as the interface between businesses and consumers. We now have over 167,000 customers, billions of consumer profiles, and hundreds of billions of customer messages and follow-on conversion data. We have a big opportunity to build state-of-the-art AI and machine learning technologies at Klaviyo to power our products and develop AI agents that can automatically create and execute marketing or customer experiences, strategies, and campaigns for any business.

Our team is looking for a Sr. AI Engineer on the Customer Agent team, Klaviyo's AI-native conversational platform. You'll play a key role in designing and building scalable backend systems and user experiences that power our AI products and AI agent solutions. You'll partner closely with product managers, machine learning engineers, and data scientists, to drive real-world impact at scale. This is a backend-heavy role with opportunities to influence architecture, async processing pipelines, distributed systems, and more.

How You Will Make a Difference

  • Design and build backend systems that support scaling our AI solutions for 167K+ customers.
  • Develop robust, reliable and scalable data collection and processing pipelines for machine learning models to train and consume.
  • Develop robust, reliable and scalable services to serve AI models in production environments.
  • Contribute to evolving our agentic architecture, making our AI agents more self-sufficient and performant.
  • Contribute to a culture of ownership, experimentation, and customer-centric product thinking.

Who You Are

  • 5-7 years of professional experience in software engineering, with a strong focus on backend systems and distributed architectures.
  • Have hands-on experience building and deploying generative AI and agentic AI applications into production, with expertise in prompt engineering, few-shot learning, fine tuning and evaluation.
  • Experienced backend engineer with a strong track record of building scalable, distributed systems, especially in the service of AI agent capabilities.
  • Proficient in Python and modern backend frameworks (FastAPI, Django preferred).
  • Experience creating human and automated evals to ensure high AI model quality.
  • Proficient in big data tools such as Apache Spark and Hadoop.
  • Deep experience with asynchronous processing and distributed task queues (Celery, Kafka, SQS, RabbitMQ, Redis).
  • Strong understanding of database technologies and ORMs (SQLAlchemy, Alembic).
  • Comfortable with cloud-native architectures (AWS) and container orchestration (Kubernetes); can manage infrastructure and CI/CD pipelines.
  • Skilled at designing and building robust APIs.
  • Able to operate with a high degree of autonomy, handle ambiguity, and thrive in a fast-moving, startup-like environment.
  • Driven by curiosity. You're someone who learns and stays up to date with this rapidly evolving field.
  • Comfortable collaborating directly with product managers and customers to shape solutions.

Nice to Have

  • Trained ML models in the past and deployed them in production systems to generate impact to businesses.
  • Experience in reinforcement learning.

We use Covey as part of our hiring and / or promotional process. For jobs or candidates in NYC, certain features may qualify it as an AEDT. As part of the evaluation process we provide Covey with job requirements and candidate submitted applications. We began using Covey Scout for Inbound on April 3, 2025.

Please see the independent bias audit report covering our use of Covey here.

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