Cumulus Labs

Cumulus Labs is a Y Combinator (W26) company building a unified inference platform for production AI. Cumulus consolidates the eight subsystems teams normally assemble from separate vendors — an OpenAI-compatible gateway, a per-workflow router, a layered prompt/KV cache, request-level observability, continuous shadow evaluation, one-click LoRA fine-tuning, custom open-weight hosting, and the proprietary Ion inference engine running on NVIDIA Grace and Blackwell GPUs — behind a single OpenAI-compatible API at api.cumuluslabs.io/v1. Ion's custom attention kernels deliver 30-50% more throughput than stock vLLM and SGLang, and the gateway is a drop-in replacement for the OpenAI, Anthropic, LangChain, LlamaIndex, and Vercel AI SDKs — change one line of configuration and keep your existing code.

Cumulus Labs publishes 1 API on the APIs.io network. Tagged areas include Company, Inference, LLM, AI Infrastructure, and GPU.

Cumulus Labs’ developer surface includes documentation, getting-started guide, API reference, engineering blog, support, authentication, and 12 more developer resources.

🌐 Visit website 📡 Source on GitHub

25.8/100 emerging ▬ flat Agent 3/100 human only saas Full breakdown ↓
scored 2026-09-08 · rubric v0.20.0

1 APIs

Company Inference LLM AI Infrastructure GPU Machine-Learning Model Serving Fine-Tuning API Gateway Y Combinator

Kin Score

Kin Score How this is scored →
scored 2026-09-08 · rubric v0.20.0

Composite quality — 25.8/100 · emerging

Contract Quality 0.0 / 25

Developer Ergonomics 11.4 / 20

Access Clarity 4.2 / 20

Operational Transparency 0.3 / 13

Contract Governance 2.2 / 12

Discoverability 7.6 / 10

Agent readiness — 3/100 · human only

Machine-Readable Contract 0 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 0 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

Create-or-Update Ergonomics could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

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APIs 1

Individual APIs this provider publishes, each with its own machine-readable definition.

Cumulus Inference Gateway

OpenAI-compatible HTTP inference gateway. One client works against every upstream provider; per-workflow routing rules pick the model, provider, and infrastructure, with a layer...

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Cumulus Labs Authentication

http · 1 scheme

SECURITY

Cumulus Labs Domain Security

TLSv1.3 · DNSSEC · DMARC

SECURITY

Resources

Get Started 2

Portal, sign-up, and the first successful call

DeveloperPortal

DeveloperPortal

GettingStarted

GettingStarted

Documentation 2

Reference material describing how the API behaves

Documentation

Documentation

APIReference

APIReference

Agent Surfaces 1

MCP servers, agent skills, and machine-readable catalogs

LLMsTxt

LLMsTxt

Design & Contract 3

Pagination, idempotency, versioning, errors, and events

Conventions

Conventions

Conformance

Conformance

Lifecycle

Lifecycle

Build 1

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

GitHubOrganization

Access & Security 2

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Authentication

Authentication

Operate 1

Status, limits, changes, and where to get help

Support

Support

Commercial 2

Pricing, plans, and the legal terms of use

TermsOfService

TermsOfService

PrivacyPolicy

PrivacyPolicy

Company 4

The organization behind the API

Website

Website

Blog

Blog

LinkedIn

Twitter

Twitter

Source (apis.yml)

aid: cumulus-labs
name: Cumulus Labs
description: Cumulus Labs is a Y Combinator (W26) company building a unified inference platform for production AI. Cumulus
  consolidates the eight subsystems teams normally assemble from separate vendors — an OpenAI-compatible gateway, a per-workflow
  router, a layered prompt/KV cache, request-level observability, continuous shadow evaluation, one-click LoRA fine-tuning,
  custom open-weight hosting, and the proprietary Ion inference engine running on NVIDIA Grace and Blackwell GPUs — behind
  a single OpenAI-compatible API at api.cumuluslabs.io/v1. Ion's custom attention kernels deliver 30-50% more throughput than
  stock vLLM and SGLang, and the gateway is a drop-in replacement for the OpenAI, Anthropic, LangChain, LlamaIndex, and Vercel
  AI SDKs — change one line of configuration and keep your existing code.
url: https://raw.githubusercontent.com/api-evangelist/cumulus-labs/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- y-combinator
- nvidia-inception
x-tier: profiled
x-tier-reason: enrichment-pass
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: false
  label: Hosted service · you call their endpoint
  confidence: medium
  source:
  - pricing
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - authentication
  - security
  generated: '2026-09-03'
  method: derived
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-07-18'
tags:
- Company
- Inference
- LLM
- AI Infrastructure
- GPU
- Machine-Learning
- Model Serving
- Fine-Tuning
- API Gateway
- Y Combinator
tags_raw:
- Company
- Inference
- LLM
- AI Infrastructure
- GPU
- Machine Learning
- Model Serving
- Fine-Tuning
- API Gateway
- Y Combinator
image: https://cumuluslabs.io/cumulus-logo/Cumulus-White.svg
apis:
- name: Cumulus Inference Gateway
  description: OpenAI-compatible HTTP inference gateway. One client works against every upstream provider; per-workflow routing
    rules pick the model, provider, and infrastructure, with a layered exact/prefix/semantic cache, request-level observability,
    and the Ion engine serving open-weight models and fine-tunes.
  humanURL: https://docs.cumuluslabs.io/
  baseURL: https://api.cumuluslabs.io/v1
  tags:
  - Inference
  - LLM
  - OpenAI-Compatible
  - Gateway
  - GPU
  properties:
  - type: Documentation
    url: https://docs.cumuluslabs.io/
  - type: GettingStarted
    url: https://docs.cumuluslabs.io/getting-started/
  - type: APIReference
    url: https://docs.cumuluslabs.io/inference/overview/
  - type: Authentication
    url: authentication/cumulus-labs-authentication.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: DomainSecurity
  url: security/cumulus-labs-domain-security.yml
- type: Website
  url: https://cumuluslabs.io/
- type: DeveloperPortal
  url: https://docs.cumuluslabs.io/
- type: Documentation
  url: https://docs.cumuluslabs.io/
- type: GettingStarted
  url: https://docs.cumuluslabs.io/getting-started/
- type: APIReference
  url: https://docs.cumuluslabs.io/inference/overview/
- type: Blog
  url: https://cumulus.blog/
- type: GitHubOrganization
  url: https://github.com/cumulus-compute-labs
- type: Support
  url: mailto:founders@cumuluslabs.io
- type: TermsOfService
  url: https://cumuluslabs.io/terms-of-service.pdf
- type: PrivacyPolicy
  url: https://cumuluslabs.io/privacy-policy.pdf
- type: LinkedIn
  url: https://www.linkedin.com/company/cumuluscomputelabs/
- type: Twitter
  url: https://x.com/cumuluslabsio
- type: Authentication
  url: authentication/cumulus-labs-authentication.yml
- type: Conventions
  url: conventions/cumulus-labs-conventions.yml
- type: Conformance
  url: conformance/cumulus-labs-conformance.yml
- type: Lifecycle
  url: lifecycle/cumulus-labs-lifecycle.yml
- type: LLMsTxt
  url: llms/cumulus-labs-llms.txt
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence

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