Which agent infrastructure startups rank highest, and who are their investors?

The highest-ranked agent infrastructure startups in SalesBook are Modal (Accel and Kleiner Perkins); Relevance AI (Bessemer Venture Partners and Insight Partners); You.com (Cox Enterprises and Georgian). Below are the top 20 of the 128 SalesBook ranks, each with the investors on its profile and a dated source.

Updated 2026-10-22 · SalesBook ranking, methodology v0.3.0 · ranks are never for sale. See also all 128 ranked.

Agentic rankings measure published agent interfaces (MCP, A2A, llms.txt) and the public evidence available, not verified Fortune 500 adoption or procurement approval.

Top 20 agent infrastructure startups and their investors

1. Modal#1Cloud infrastructure for AI teams: GPU inference, training, serverless functions and isolated Sandboxes for coding agents and untrusted code.
   Investors: Accel, Kleiner Perkins, Menlo Ventures, General Catalyst, Redpoint, Lux Capital, Amplify Partners, Bain Capital Ventures · Source: modal.com, checked 2026-10-22
2. Relevance AI#2Platform for enterprise teams to build and run AI agents for sales, support, marketing and operations.
   Investors: Bessemer Venture Partners, Insight Partners, Peak XV, King River Capital · Source: smartcompany.com.au, checked 2026-10-22
3. You.com#3Web search, contents and research APIs for AI agents and LLM developers, with enterprise plans.
   Investors: Cox Enterprises, Georgian, Salesforce Ventures, Norwest · Source: about.you.com, checked 2026-10-22
4. Merge#4Unified API and Agent Handler that give software companies' AI agents authenticated, scoped access to third-party tools, with audit logs.
   Investors: Accel, NEA, Addition · Source: merge.dev, checked 2026-10-22
5. Vapi#5Developer and enterprise platform for building, testing and deploying voice AI agents for phone and web calls.
   Investors: Peak XV, Y Combinator, M12, Kleiner Perkins · Source: vapi.ai, checked 2026-10-22
6. WorkOS#6APIs for enterprise SSO, directory sync, audit logs and AuthKit, including auth for MCP servers and AI agents, sold to SaaS companies.
   Investors: Greenoaks, Lightspeed Venture Partners · Source: techcrunch.com, checked 2026-10-19
7. Braintrust#7Observability and evaluation platform for AI agents in production: tracing, LLM/code/human scoring, experiments and datasets for engineering and product teams.
   Investors: ICONIQ, Andreessen Horowitz, Greylock · Source: braintrust.dev, checked 2026-10-22
8. Dust#8Platform for companies to build, share and govern AI agents connected to company knowledge and tools.
   Investors: Abstract, Sequoia, Snowflake, Datadog · Source: tech.eu, checked 2026-10-22
9. Synthflow#9Enterprise AI voice agent platform with its own telephony, used by contact centers, BPOs and enterprises to automate phone calls.
   Investors: Accel, Atlantic Labs, Singular · Source: synthflow.ai, checked 2026-10-22
10. Comet (Opik)#10Opik, an open-source LLM and agent observability and evaluation platform, plus ML experiment management, sold to AI/ML teams and enterprises.
    Investors: OpenView, Scale Venture Partners, Trilogy Equity Partners, Two Sigma Ventures · Source: comet.com, checked 2026-10-22
11. StackOne#11Integration infrastructure for AI agents: 560+ connectors and 35,000+ actions with managed auth, an MCP gateway and prompt-injection defense.
    Investors: GV, Workday Ventures, XTX Ventures, Episode 1, Playfair · Source: stackone.com, checked 2026-10-22
12. Profound#12AI visibility platform that shows brands how answer engines such as ChatGPT and Perplexity describe them, with agents that act on marketing tasks.
    Investors: Lightspeed Venture Partners, Sequoia Capital, Kleiner Perkins, Saga VC, South Park Commons · Source: fortune.com, checked 2026-10-19
13. Weaviate#13Open-source vector database and AI platform for search, RAG and agents, offered as shared or dedicated cloud to AI teams and enterprises.
    Investors: Index Ventures, Battery Ventures · Source: siliconcanals.com, checked 2026-10-22
14. Temporal#14Open-source durable execution platform and Temporal Cloud for running reliable applications and AI agents, sold to developers and enterprises.
    Investors: Andreessen Horowitz, Lightspeed Venture Partners, Sapphire Ventures, Sequoia Capital, Index Ventures, Tiger Global Management, GIC, Madrona Venture Group, Amplify Partners · Source: thesaasnews.com, checked 2026-10-22
15. Exa#15Search API built for AI agents that returns real-time web results and page content, sold pay-as-you-go and to enterprises.
    Investors: Benchmark, Lightspeed Venture Partners, Y Combinator, NVentures · Source: lw.com, checked 2026-10-19
16. LlamaIndex#16Document agent and parsing platform (LlamaParse) plus open-source LlamaIndex framework for building agents over enterprise documents.
    Investors: Norwest Venture Partners, Greylock Partners · Source: llamaindex.ai, checked 2026-10-22
17. LangChain#17Open-source agent frameworks (LangChain, LangGraph) plus LangSmith, a paid platform for building, tracing, evaluating and deploying agents for companies.
    Investors: IVP, Sequoia Capital, Benchmark, CapitalG · Source: fortune.com, checked 2026-10-19
18. Raindrop#18Monitoring and issue detection for AI agents in production: tracing, silent-failure detection, triage and simulations for teams shipping agents.
    Investors: Lightspeed Venture Partners, Figma Ventures, Vercel Ventures, Y Combinator · Source: raindrop.ai, checked 2026-10-22
19. Nango#19Open-source, code-first integration platform that connects products and AI agents to 1,000+ APIs with auth, syncs, webhooks and MCP tools.
    Investors: Gradient, Horizon, Y Combinator · Source: nango.dev, checked 2026-10-22
20. Retell AI#20Voice AI agent platform for inbound and outbound phone calls, with chat and SMS, sold to healthcare, financial services and other enterprises.
    Investors: Alt Capital, Y Combinator, Carya Venture · Source: retellai.com, checked 2026-10-22

Questions

Which agent infrastructure startups rank highest, and who are their investors?

The highest-ranked agent infrastructure startups in SalesBook are Modal (Accel and Kleiner Perkins); Relevance AI (Bessemer Venture Partners and Insight Partners); You.com (Cox Enterprises and Georgian). Below are the top 20 of the 128 SalesBook ranks, each with the investors on its profile and a dated source.

How is this list ranked?

In SalesBook rank order under methodology v0.3.0, built only from dated public sources. Rankings are never for sale.

When was this list last updated?

2026-10-22: the most recent date a company on this list was checked against its public sources.