--- id: hermes-goes-on-the-wire-as-mcp title: Hermes never set clientInfo, so servers saw the SDK's placeholder name kind: gap summary: At `a24c12d1` Hermes passed no `client_info`, so handshakes carried the SDK placeholder `mcp` 0.1.0. At `9dcf7714` it sends `hermes-agent` with its base version, as the probe saw on the wire. Older builds still send `mcp`. capabilities: - clientInfoNames clients: - hermes-agent specVersions: - 2025-11-25 sources: - url: https://github.com/NousResearch/hermes-agent title: tools/mcp_tool.py, ClientSession construction on the stdio and HTTP paths commit: a24c12d1 path: tools/mcp_tool.py:3260-3266,3342-3344,3725,3796,3844 date: 2026-08-27 - url: https://pypi.org/project/mcp/2.0.0/ title: mcp 2.0.0, DEFAULT_CLIENT_INFO and the client_info fallback path: mcp/client/session.py:66,381,391 date: 2026-08-27 - url: https://github.com/NousResearch/hermes-agent title: tools/mcp_tool_transport.py, _session_kwargs now passes client_info commit: 9dcf7714 path: tools/mcp_tool_transport.py:171-186 date: 2026-11-09 - url: https://github.com/NousResearch/hermes-agent title: hermes_platform/resolver/app.py, desktop-app liveness probe commit: 9dcf7714 path: hermes_platform/resolver/app.py:405-415 date: 2026-11-09 status: stale lastVerified: 2026-11-09 related: - goose-client-name-varies-by-surface - codex-prefers-a-chatgpt-hosted-client-identifier canonical: https://canimcp.io/research/hermes-goes-on-the-wire-as-mcp last-updated: 2026-11-11 --- # Hermes never set clientInfo, so servers saw the SDK's placeholder name Kind: gap · Status: stale · Last verified: 2026-11-09 · Clients: [hermes-agent](/clients/hermes-agent.md) · Revisions: `2025-11-25` ## Update, 2026-11-09 At `9dcf7714`, `_session_kwargs` passes `client_info=Implementation(name="hermes-agent", version=get_version_info().base_version)` on every configurable session, with the comment "Servers key logs/behaviour on clientInfo; the SDK default is "mcp"/"0.1.0"". The probe run against build `0.23.0+689.ga9ff979` recorded `"clientInfo":{"name":"hermes-agent","version":"0.23.0"}`. The note below describes `a24c12d1` and is kept for older builds, which still send `mcp`. Hermes now puts three names on the wire. `hermes-agent` is the real session. `hermes-probe` is the non-MCP-endpoint preflight frame described below, unchanged. `hermes` with version `probe` is a new hand-written `initialize` at `2025-06-18` that checks whether a declared desktop app's loopback MCP endpoint is answering. The internal `cua-driver` computer-use session is still constructed bare and sends `mcp`, but it talks only to a binary Hermes ships. ## At a24c12d1 `ClientSession.__init__` takes an optional `client_info` and falls back to `DEFAULT_CLIENT_INFO`, which mcp 2.0.0 defines as `Implementation(name="mcp", version="0.1.0")`. Hermes builds its session kwargs from the sampling handler, the elicitation handler, a message handler and a logging callback. `client_info` is not among them at any of the four construction sites, so the fallback applies on every connection, on both transports. The name is not merely generic — it is the SDK's own placeholder, shared with every Python client that also declines to set it. A server writing per-client compatibility shims, or rate-limiting by caller, has nothing to key on. `2026-07-28`'s per-request `_meta` envelope carries the same value, so the modern path does not fix it either. This has a direct consequence for the observed tier. The Hugging Face client telemetry feed identifies callers by the name in `clientInfo`, so Hermes traffic either never appears or appears aggregated under `mcp` alongside unrelated clients. Any observed-tier row attributed to `mcp` cannot be attributed to a client at all. There is one place Hermes does name itself. When a configured URL answers with a content type that is not an MCP media type, it POSTs a hand-written minimal `initialize` frame at `2025-03-26` with `clientInfo.name` of `hermes-probe` to decide whether the endpoint speaks MCP before reporting a `NonMcpEndpointError`. That frame is a diagnostic and never carries a real session, so `hermes-probe` is the only recognisable name Hermes puts on the wire and it appears only on endpoints that failed a content-type check. Recorded as a gap rather than an idiosyncrasy: the SDK provides the field, Hermes has a name, and nothing in the code suggests the omission was decided. ## Sources - [tools/mcp_tool.py, ClientSession construction on the stdio and HTTP paths](https://github.com/NousResearch/hermes-agent), commit `a24c12d1`, `tools/mcp_tool.py:3260-3266,3342-3344,3725,3796,3844`, 2026-08-27 - [mcp 2.0.0, DEFAULT_CLIENT_INFO and the client_info fallback](https://pypi.org/project/mcp/2.0.0/), `mcp/client/session.py:66,381,391`, 2026-08-27 - [tools/mcp_tool_transport.py, _session_kwargs now passes client_info](https://github.com/NousResearch/hermes-agent), commit `9dcf7714`, `tools/mcp_tool_transport.py:171-186`, 2026-11-09 - [hermes_platform/resolver/app.py, desktop-app liveness probe](https://github.com/NousResearch/hermes-agent), commit `9dcf7714`, `hermes_platform/resolver/app.py:405-415`, 2026-11-09 ## Related notes - [goose-client-name-varies-by-surface](/research/goose-client-name-varies-by-surface.md) - [codex-prefers-a-chatgpt-hosted-client-identifier](/research/codex-prefers-a-chatgpt-hosted-client-identifier.md)