OpenRouter
One API for every model — routing, pricing and fallbacks.
OpenRouter is the unified API for frontier and open models: one endpoint, per-token billing across providers, automatic fallbacks and routing by price, latency or capability. Bootstrapped and profitable, it became the default way provider-agnostic harnesses reach every model.
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Modal
Serverless cloud built for AI and agentic compute.
Modal lets teams run inference, fine-tuning and arbitrary agent workloads as serverless Python without managing infrastructure — a common substrate for harness backends at scale.
Temporal
Durable execution for long-running agent workflows.
Temporal's durable execution engine is widely adopted to make agent pipelines reliable: state survives crashes, retries are automatic, and workflows run for minutes or months. A key piece of serious harness infrastructure.
Inngest
Durable functions and workflows for AI agents.
Inngest runs agent logic as durable steps — queueing, retries, concurrency control and human-in-the-loop waits — without operating your own workflow infrastructure.