Top Series B companies in San Francisco

Companies that have closed a Series B - proven scaling motion, hiring aggressively. Filtered to companies headquartered in San Francisco.

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Ranked by current headcount across Series B companies headquartered in San Francisco. Refreshed monthly.

1
Railway· San Francisco, California, United States
Railway’s mission is to build the cloud computing stack that unburdens you, so you can focus more on what matters to you.
- Series B
- 11.4k employees
- Founded 2020
2
Grammarly· San Francisco, California, United States
Grammarly stands with Ukraine. We invite you to do the same. Here are some ways you can help: gram.ly/WeStandWithUkraine ---Grammarly is the world’s leading AI writing assistance company trusted by over 40 million people and 50,000 organizations every day. From instantly creating a first draft to perfecting every message, Grammarly helps people at 96% of the Fortune 500 get their point across—and get results—without compromising security or privacy. We believe that great writing gets work done. Grammarly’s product offerings—Grammarly Business, Grammarly Premium, Grammarly Free, and Grammarly for Education—work where you do, delivering contextually relevant writing support across over 500,000 apps and websites. Founded in 2009, Grammarly is No. 7 on the Forbes Cloud 100, one of TIME’s 100 Most Influential Companies, one of Fast Company’s Most Innovative Companies in AI, and one of Inc.’s Best Workplaces. Grammarly offers a dynamic hybrid working model. This approach helps foster trust, innovation, and a strong team culture, with the flexibility of working from home, whenever you need focus time.
- Series B
- 9.8k employees
- Founded 2009
3
GitHub· San Francisco, California, United States
As the global home for all developers, GitHub is the complete AI-powered developer platform to build, scale, and deliver secure software. Over 100 million people, including developers from 90 of the Fortune 100 companies, use GitHub to build amazing things together across 330+ million repositories. With all the collaborative features of GitHub, it has never been easier for individuals and teams to write faster, better code.
- Series B
- 6.8k employees
- Founded 2008
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4
Driver· San Francisco, California, United States
Based in San Francisco and Shanghai, Driver is a technology platform that connects cancer patients to treatments and knowledge, all over the world, to get more life. With an app for the patient and an app for the doctor, Driver’s platform enables any cancer patient, regardless of their location, to access treatment options across Driver’s global network of cancer centers without leaving home. Driver’s network includes over 30 of the world’s leading cancer centers, including its founding members the US National Cancer Institute and the Chinese National Cancer Center. Other members of Driver’s network include the Cleveland Clinic, Mayo Clinic, Massachusetts General Hospital, University of California San Francisco, University of California Los Angeles, Duke, University of North Carolina, and Emory. Driver was founded in 2015 by two physicians, Dr. William R. Polkinghorn and Dr. Petros Giannikopoulos, and Driver’s lead investor is Horizons Ventures (Li Ka Shing).
- Series B
- 6.5k employees
- Founded 2015
5
Sama· San Francisco, California, United States
What Does Sama DoSama gets your AI project to production—and helps you stay there.Sama is chosen by high-performing GenAI and CV teams across the full AIdevelopment lifecycle, combining expert services with reliable execution thatscales—delivering results, dependable datasets, and continuity even as things change.Our services cover the full AI lifecycle:● Data Strategy & Consulting – Aligning data needs to model goals, definingquality standards, and setting the foundation for faster, more confidentdevelopment● Annotation & Labeling – Using full-time, domain-trained teams with built-in QA to deliver precise, production-ready training data.○ Annotation Workflows: Validation, Classification, Tagging, Enrichment○ GenAI Workflows: Prompt Engineering, RAG embedding, Retrieval-AugmentedGeneration (RAG), Content Moderation & Filtering...● Model Evaluation – Scoring, ranking, and validating model outputs throughstructured, rubric-based evaluation and human-in-the-loop reviewWe don’t just deliver data—we embed in your workflows. Our dedicated teams,integrated QA, and platform support accelerate time-to-quality and give you the control and flexibility needed to iterate with speed and confidence.
- Series B
- 4.4k employees
- Founded 2008

6
Forage· San Francisco, California, United States
Everybody wins when workforces are diverse. But while talent is everywhere, opportunity is not. Since 2017, Forage has worked with the world’s top employers to create job simulations designed for students to build career skills, visibility, and confidence. We connect talent and ambition to opportunity. Forage is also proud to be Great Place to Work certified. This year, 97% of employees said Forage is a great place to work—40 points higher than the average US company!Forage is headquartered in San Francisco with offices in New York, London, Sydney and teammates working globally.
- Series B
- 1.6k employees
- Founded 2017
7
Constructor· San Francisco, California, United States
Constructor is the only search and discovery platform designed exclusively for commerce where conversions matter. Our platform delivers unmatched KPI optimization and fast ROI for enterprise ecommerce brands, retailers, distributors, marketplaces, and more — while giving customers a personalized, enjoyable shopping experience. Unlike other platforms, Constructor is the only search and product discovery solution that was built from the ground up with clickstream data and advanced AI, not merely bolted onto a legacy keyword engine. Consistently outperforming competitors in A/B tests, Constructor’s solutions use generative AI and collaborative personalization to deliver compelling user experiences across all aspects of product discovery. From search and browse, to AI Shopping Agents and Product Insights Agents, recommendations, collections, offsite discovery, attribute enrichment, and much more, Constructor covers the entire discovery journey.Optimizing specifically for ecommerce metrics like revenue, conversion rate and profit, Constructor generates consistent $10M+ revenue lifts for our customers, which include some of the world’s most recognized brands, like Sephora, Under Armour, Petco, and many more.Constructor is the only search and discovery vendor named a Leader by Forrester, Gartner and IDC. Want to hear from our customers? See what they have to say about us at G2 or Gartner Peer Insights.Learn more at constructor.com.
- Series B
- 1.4k employees
- Founded 2015
8
Courier· San Francisco, California, United States
Courier is the customer messaging and notifications platform where your team and AI agents collaborate. Orchestrate notifications, power lifecycle journeys, personalize with AI intelligence, and deliver across email, SMS, push, chat, in-app, Slack, and Microsoft Teams.
- Series B
- 1.2k employees
- Founded 2019
9
Fast· San Francisco, California, United States
One-click checkout. Zero hassle. Sign up in a minute, check out in a second.
- Series B
- 1.1k employees
- Founded 2019
10
Robosoft Technologies· San Francisco, California, United States
Engineering the Experience that matter.A full-stack digital partner for what’s next, Robosoft builds people‐centric digital solutions powered by the global scale of TechnoPro and Blackstone.With nearly three decades of experience, we combine human understanding with engineering excellence to help organizations grow, adapt, and thrive.Robosoft helps enterprises design and engineer intelligent digital systems where experience, software, and AI converge. From mobile, web, application, and software-defined platforms, we build human-centered technology that is intuitive to use, resilient by design, and ready to evolve.At the heart of everything we do is a simple belief: Technology should serve people and the outcomes they care about. We bring together human insight, product thinking, and deep engineering to create meaningful digital experiences and intelligent systems. Our work is modern, resilient, and built for impact approached with humility, care, and respect for the responsibility our clients place in us.
- Series B
- 1.1k employees
- Founded 1996

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Find engineers at Series B companies in San Francisco

Series B companies in San Francisco are some of the fastest-moving employers in the market. The list above ranks the largest Series B-stage companies headquartered in San Francisco by current headcount, drawn from public LinkedIn and Crunchbase records. With 492 matching companies in Refolk’s index, the density of senior engineers, designers, and founders is unusually high.

At Series B, teams tend to be small, ambitious, and on the hunt for senior talent. The companies on this list are good signals for where the San Francisco talent market is heating up - and for which engineers and founders are about to become tomorrow’s operators.

Refolk converts this list into a live search. Ask for “founders of Series B companies in San Francisco” or “senior engineers at Series B companies in San Francisco hiring” and Refolk returns a ranked shortlist with evidence behind each match.

How this list is built

Refolk pulled Series B companies headquartered in San Francisco from public LinkedIn and Crunchbase records, ranked them by current employee count, and kept those with at least 5 employees. The list refreshes monthly.

Last refreshed: Fri, 18 Sep 2026 07:49:52 GMT

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How is this ranking built?

The list draws on the public company graph - headcount and growth signals, funding history, and recency. The criteria chips at the top show exactly which filters produced it, and the methodology section explains the ranking.

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