Series A AI companies in San Francisco

Redrob - 'border' in reverse - is building LLMs for the next 3 billion. Purpose-built for sales, recruitment, and jobs. Series A funded with $14M. Backed by world-class VCs.

• Series A
• 218 employees
• Founded 2018

Created by researchers from UC Berkeley, Arena (formerly LMArena) is a community-powered platform to measure and advance the frontier of AI for real-world use. Tens of millions of builders, researchers, and creative professionals come to Arena to use frontier models and give feedback on their responses, shaping a public leaderboard grounded in real-world use.

• Series A
• 96 employees
• Founded 2025

At Rime, we're on a mission to make voice AI feel more human.We bring deep linguistic and machine learning expertise to the problem of bridging the gap between humans and machines.Our technology is designed to bring warmth, authenticity, and emotional nuance to digital interactions, making conversations with machines feel more like conversations with real people.And our voices drive real results, like 15%+ call success, 23%+ increased sales, and 25%+ IVR containment for high growth startups and fortune 500 brands.

• Series A
• 51 employees
• Founded 2021

Essential AI is on a mission to make frontier AI more accessible through an open, collaborative platform. Our open models, robust tooling, reproducible pipelines, and evaluation frameworks empower anyone to build, iterate, and innovate at pace.Powerful AIs don't trace their origins to singular breakthroughs, but from an amalgam of improvements, incremental and large. Essential AI creates the ideal environment to catalyze these advancements, enabling a steady path to sustained frontier capabilities.By incrementally releasing frontier-capable models alongside sharing significant open science components, we translate research into real-world impact. In the near term, this accelerates discoveries, broadens adoption, and draws new talent into our ecosystem, equipping emerging domains with open models as the essential entry point to tackle critical challenges. Over the long run, it shapes AI’s evolution globally and sustains scalable, durable business models through strategic API and domain partnerships -partnering with the world’s builders to drive relentless, frontier-level innovation.

• Series A
• 22 employees
• Founded 2023

Timeless Way is an R&D organization currently operating in stealth.

• Series A
• 8 employees
• Founded 2026