William Lehmann

Founder & GP at Step Function

📍 United States🔄 Updated September 2026💼 32 investments📅 13 years investing🗓 Last invested Jun 2026
VC🌍 United States20+ investmentsInvested this quarter
32
Total investments
20
Early stage
6
Mid stage
2
Late stage
13y
Years active

Portfolio

32 investments · sorted by recency
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Mid stage
Late stage
Seed Investor
Jun 2026
Most breaches start with human behavior. Sidekick security is the first forward-deployed cybersecurity program that puts an expert team of guardian agents beside every user, protecting the moments where decisions create risk. Social engineering. Identity threats. Shadow SaaS. AI usage. Internet browsing. The click, the credential, the decision. Secure the human. Secure the business. About Sidekick Security + Sidekick Labs, Inc. Sidekick Labs is pioneering a new category of cybersecurity built for the human edge - the moments where employee decisions create enterprise risk. Its flagship platform, Sidekick, forward-deploys a team of expert guardian agents beside every user, at the point of decision to defend against social engineering, identity threats, shadow SaaS, AI misuse, and risky browsing. Founded by the cybersecurity veterans behind Randori, Sidekick Labs is headquartered in Boston and Denver. Learn more at sidekicksecurity.ai.
Seed Investor
Apr 2026
Development and knowledge systems for the agentic era
Seed Investor
Nov 2025
Solving what was once thought unsolvable in one of cybersecurity’s largest markets.
Seed Investor
Oct 2025
Global Voice AI Infrastructure - local to every customer Extending your voice stack across regions, models, and runtimes — compliant by default
Seed Investor
May 2025
AI Agents promise transformative benefits but effective adoption is impossible without the right controls, and existing tools can’t keep pace with autonomous behaviour. At Geordie, we help enterprises accelerate agentic innovation without unleashing risk - giving Security & IT teams an agent-native platform to understand agents, proactively mitigate exposure, and safely scale adoption. Our platform delivers posture management, observability, and contextual interventions. Turning blind spots into visibility and unmanaged exposure into governed outcomes. With Geordie, enterprises gain the confidence to adopt AI agents securely, responsibly, and at scale.
Seed Investor
Mar 2025
Pavo builds systems-first intelligence for the enterprise: self-evolving knowledge systems, agent societies, and world models that learn from experience to optimize business outcomes.
Seed Investor
Jan 2025
Datum is building the world’s first open network cloud — a neutral place where Alt Clouds, tech incumbents, and digital leaders can programmatically interact with their unique ecosystem. Our mission is to help 1k new clouds thrive in the AI era by unlocking "internet superpowers" for every builder. Our vision is to be the most trusted way for digital ecosystems to interact, with millions of intelligent connections to prove it. Datum has a strong belief in transparency and building trust with builders. Core components are released under the AGPLv3 license, giving users full visibility and audit capability, the ability to adapt and self-host if needed, and long-term confidence without vendor lock-in.
Seed Investor
Jan 2025
Unkey is an open source API management platform that helps developers secure, manage, and scale their APIs. Unkey has built-in features that can make it easier than ever to provide an API to your end users, including: - Per key rate limiting - Limited usage keys - Time-based keys - Per key analytics
Seed Investor
Jul 2024
Nebulock is the first agentic threat hunting platform; autonomously surfacing behaviors, not just IOCs, from your existing data. Nebulock acts like a new teammate: a 24/7 AI threat hunter that investigates hypotheses, reasons through your telemetry, and learns from your environment. Whether you’re a two-person SOC or a global enterprise, we scale your threat hunting—and give your team superpowers. Today, threat hunting is broken. Security teams spend weeks chasing alerts, writing detections by hand, and manually validating findings—often just to confirm what their existing tools already flagged. Meanwhile, attackers exploit credentials, move laterally, and operate in silence. Nebulock flips the model. We continuously and autonomously hunt across endpoint, identity, and cloud telemetry—identifying the subtle behavioral signals that point to credential misuse, lateral movement, insider threats, and post-access activity. Then we turn those hunts into hardened, behavior-based detections—automatically. No new agents
No alert regurgitation No workflow disruption Just high-fidelity, explainable findings—delivered directly to your SIEM, API, or Slack.
Seed Investor
May 2024
An Enterprise Orchestration and Observability PaaS, enabling enterprises of tomorrow to go from code to global scale in seconds. #ModuleFederation, #MicroFrontends, #ComposableSoftware
Seed Investor
Apr 2024
Lunar.dev is the infrastructure layer for governing outbound API traffic in the age of agentic AI. Built for engineering teams running at scale, Lunar.dev provides a production-grade gateway to manage and optimize traffic from AI-powered applications, including LLM calls, third-party APIs, and Model Context Protocol (MCP) interactions. Our platform gives your team visibility, policy enforcement, and active controls over API consumption. It helps you move from experimentation to safe, scalable deployment. Whether youre looking to implement token-aware rate limits, cost-based routing, or access controls for autonomous agents, Lunar.dev gives you the tools to get there.
Seed Investor
Mar 2024
S3 for Data
Seed Investor
Dec 2023
Electric is a Postgres sync engine. Use it to sync little subsets of your data into local apps and services.
Seed Investor
Dec 2023
Proofs AI Agents generate code for customized Proof-of-Concepts (PoCs) and full-stack applications, enabling sales engineering teams to build working software demonstrations in hours instead of weeks. Our platform dramatically cuts PoC development costs from tens of thousands to just hundreds of dollars while shortening sales cycles and improving conversion rates. The Problem We Solve: Building tailored PoCs traditionally takes weeks to months and $10K-$100K+ in engineering time per prospect. This bottleneck slows deals, inflates customer acquisition costs, and wastes scarce technical talent on demo-ware that serves only a fraction of prospects. Our Solution: Proofs deploys autonomous AI agents that assemble fully working, brand-aligned PoCs in hours. The platform ingests your prospects preferred tech stack, APIs, and data, then produces deploy-ready code complete with customized configurations, branding, copy, data, and use-case flows. Bring Your Own Tech Stack: Our platform supports virtually any modern tech stack. Examples include: - Modern frameworks (React, Next.js, FastAPI, Streamlit) - Data platforms (Snowflake, Supabase, PostgreSQL) - CMS solutions (Contentful, Contenstack, Akeneo) - E-commerce (Shopware, NextJS Commerce) - Full-stack capabilities (front-end interfaces, back-end functionality, APIs, infrastructure) Our mission: To build what your prospects actually want to buy. Let your prospects experience your solution in their environment before signing a contract. Proofs turns sales conversations into immediate product experiences that resonate with buyers.
Show all 32 investments ↓
Experience · 34 entries
All (34)
Investments (32)
Founder (1)
Board (11)
2026
Seed Investor
Jun 2026
Most breaches start with human behavior. Sidekick security is the first forward-deployed cybersecurity program that puts an expert team of guardian agents beside every user, protecting the moments where decisions create risk. Social engineering. Identity threats. Shadow SaaS. AI usage. Internet browsing. The click, the credential, the decision. Secure the human. Secure the business. About Sidekick Security + Sidekick Labs, Inc. Sidekick Labs is pioneering a new category of cybersecurity built for the human edge - the moments where employee decisions create enterprise risk. Its flagship platform, Sidekick, forward-deploys a team of expert guardian agents beside every user, at the point of decision to defend against social engineering, identity threats, shadow SaaS, AI misuse, and risky browsing. Founded by the cybersecurity veterans behind Randori, Sidekick Labs is headquartered in Boston and Denver. Learn more at sidekicksecurity.ai.
Seed Investor
Apr 2026
Development and knowledge systems for the agentic era
2025
Seed Investor
Nov 2025
Solving what was once thought unsolvable in one of cybersecurity’s largest markets.
Seed Investor
Oct 2025
Global Voice AI Infrastructure - local to every customer Extending your voice stack across regions, models, and runtimes — compliant by default
Show all 34 entries ↓
Investment activity
2013–2026 · 32 investments
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