Nexus Leads $4M Seed for Lightsage’s Agent-Led Growth Platform
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Lightsage, a San Francisco, California startup that helps software companies sell to AI agents rather than just to people, has raised $4 million to build what it calls agent-led growth. The company announced the round on September 8, 2026.
Nexus Venture Partners led the Seed round. A long list of operator angels joined, including Postman CEO Abhinav Asthana, DocuSign President Robert Chatwani, Apollo CEO Matt Curl, and former Salesforce CTO Steven Tamm.
The company, incorporated as API-Rex Inc., argues that software vendors are no longer selling only to humans. With coding agents such as Claude Code, Microsoft Copilot, and Cursor doing more of the engineering work, developers increasingly let those agents pick the tools rather than reading documentation or scrolling through websites themselves. That means marketing has to reach the agents directly, which calls for a different playbook.
Lightsage’s platform runs simulations across multiple coding agents and answer engines so a vendor can see its product the way an autonomous agent does. It hands agents realistic integration tasks, sends them shopping, and measures how visible a customer’s software is against competitors. It then has the agent actually use the product. When the agent fails, the platform diagnoses why, whether the cause is confusing documentation, broken API endpoints, flawed authentication, or an incompatible Model Context Protocol server, and shows the customer how to fix it. Vendors also get analytics on agent traffic to their sites, including which agents use their software, for what tasks, and how often.
For now the focus is developer software, where AI agents are already widespread. Reducto, Daytona, Firecrawl, Rime, and Tinyfish have used the platform to understand why agents choose them in some cases and rivals in others. Founded by CEO Jun Liang Lee and CTO Sean Er, Lightsage plans to grow its commercial and engineering teams and extend its analytics, attribution, evaluation, and optimization capabilities across APIs, SDKs, command line tools, and agent skills, with a longer-term aim of bringing the approach to B2B software, cloud infrastructure, and automated payments.
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