Hermes API: Run the Hermes Agent Behind Your Product

Short answer

To run Hermes behind a product, use it as a hosted agent harness: HarnessRouter exposes Hermes through a unified API with tasks, sessions, streaming, files, and results, so your application sends a task over HTTP and gets back a recorded, reviewable run without operating the harness itself.

• Hermes is Nous Research's autonomous agent: a complete harness with toolsets, a skills system, persistent memory, MCP integration, and configurable model providers.
• Through HarnessRouter, Hermes runs behind one API with unified requests, streaming, sessions, files, artifacts, and error handling.
• Pair Hermes with a model deliberately: in the published same-task benchmark, Hermes configurations recorded both the fastest run and the lowest-cost successful run, with very different profiles.

What Hermes is

Hermes is an autonomous agent from Nous Research, documented as a self-improving agent with CLI usage, toolsets, a skills system, persistent memory, MCP integration, and configurable model providers. In harness terms it is a complete agent harness: it runs the loop, manages context, exposes tools and skills, and works on a real project workspace with shell and file access, completing tasks end to end. Search interest in Hermes broke out during 2026, and the practical question that follows is how to run it programmatically.

• General agent work, not only coding: Hermes operates on a workspace with shell and file access.
• Skills and toolsets extend what the model can do inside a task.
• Model choice is configurable, which makes Hermes a natural fit for configuration-level comparison.

The API shape: tasks in, recorded runs out

HarnessRouter supports Hermes as an available base harness with completed adapter and capability coverage: unified request, streaming, session, file and artifact, and error handling. The contract represents work, not messages:

Input

A product task, the hermes harness selection, a model from the current catalog, optional files, and execution policy.

Lifecycle

A durable session with status, streamed progress events, continuation, and cancellation.

Output

Structured results, generated files and artifacts, and a recorded execution trace for every run.

Pair Hermes with a model deliberately

Do not hardcode a model default; fetch the current catalog and allowed models from the API. The pairing decides the run's profile. In HarnessRouter's published same-task benchmark, eight harness and model configurations ran identical work five times each, and Hermes configurations recorded both ends of the useful frontier:

• The fastest configuration in the benchmark was Hermes with GPT-5.5, completing the task in 85 seconds.
• The lowest-cost successful run was Hermes with GPT-5.2 at 0.47 credits, 99.8% below the costliest recorded configuration.
• The fastest and the cheapest were different configurations, so pick per task: latency-sensitive features and cost-sensitive batch work want different pairings. Results vary by task.

Running your first Hermes task

• Create a key and send a task to the hermes harness through the quickstart; building and integration are free, and credits are used only when tasks run.
• Stream progress into your product UI, then fetch results, files, and artifacts when the run completes.
• Continue the session for follow-up work instead of restarting from zero.
• Compare a Hermes configuration against Codex and Claude Code on your own task through the same API, with each run's execution trace recorded for the comparison, before committing a workload.

FAQ

Is Hermes an agent harness?

Yes. Hermes is a complete agent harness from Nous Research: it runs the execution loop, manages context and memory, exposes toolsets and skills, and completes tasks on a real workspace with shell and file access.

Can I choose which model Hermes uses?

Yes. Hermes supports configurable model providers, and through HarnessRouter you select the model per task from the current catalog. Fetch the catalog from the API rather than hardcoding a default.

What does it cost to run Hermes through HarnessRouter?

Building and integration are free; credits are used only when tasks run. In the published same-task benchmark, the lowest-cost successful run was a Hermes configuration at 0.47 credits, though cost varies by task and model pairing.

How is running Hermes through an API different from using its CLI?

The CLI is for a developer at a terminal. The API is for a product: your application submits tasks over HTTP, streams progress to end users, persists sessions and files, and receives artifacts and execution traces, without installing or operating the harness.