hermes-plugin-solstice

Solstice model provider for Hermes Agent: run Hermes on your own per-user Gemini quota, signed in with Google through the Nous portal.

This plugin used to ship inside Hermes (plugins/model-providers/solstice/). It now lives in its own repo, so new models and fixes reach you as soon as they land here instead of waiting for a Hermes release. Version 0.2.0 adds Gemini 4 Argon (gemini-4-argon).

Solstice is pre-release. It stays out of the provider pickers, setup lists and accounts tab until you sign in by name. After that it is listed like any other signed-in provider.

Requirements

• Hermes Agent 0.22.0 or newer (hermes --version). Argon's request handling (thinking level, resuming long answers) is in Hermes core and arrived in 0.22.0. The plugin refuses to install on older releases.
• A Nous Portal sign-in (hermes auth add nous) on an account with Solstice access.

Install

hermes plugins install NousResearch/hermes-plugin-solstice
hermes auth add solstice          # skip this if you already signed in to the built-in version
hermes model                      # or: hermes config set model.provider solstice

The plugin starts working as soon as it is installed. It is a model-provider plugin, so it needs no hermes plugins enable. If the installer says "installed but not enabled", ignore it; hermes plugins list shows it as enabled.

Plugins are installed per profile. For a named profile, add -p <profile> to each command: hermes -p work plugins install NousResearch/hermes-plugin-solstice.

To try a model directly:

hermes chat --provider solstice -m gemini-4-argon

Models offered: gemini-3.1-pro-preview (default), gemini-4-argon, gemini-3.8-flash, gemini-3.5-flash-lite. Each model has its own quota. When a model runs out, Google returns HTTP 429 or 402 ("usage limit"). Switch to another model; Flash Lite is listed last as the one to fall back to.

Migrating from the built-in version

If you already use Solstice on Hermes 0.22.x, installing this plugin is the whole migration.

1. Check your version: hermes --version must say 0.22.0 or newer. If not, run hermes update first.

2. hermes plugins install NousResearch/hermes-plugin-solstice (repeat with -p <profile> for each profile that uses Solstice).

3. Restart anything that is running Hermes so it loads the plugin: the gateway (hermes gateway restart), the desktop app, and any open hermes sessions.

4. Check it is active:

   hermes plugins list | grep solstice                 # solstice ... enabled ... 0.2.0 ... git
   hermes chat --provider solstice -m gemini-4-argon -q "hi" --oneshot

What carries over without any action:

• Your sign-in. The plugin registers the same provider name (solstice, alias solstice-oauth) and reads the same saved credential in auth.json. You do not sign in again.
• Your config. model.provider: solstice, saved model choices, fallback chains and cron jobs that name solstice keep working unchanged.

Why this is safe on a release that still bundles Solstice: when a plugin in your ~/.hermes/plugins/ registers a provider with the same name as a built-in one, Hermes uses the installed plugin. The bundled copy is still on disk, but it is no longer used.

Updating

hermes plugins update solstice

Then restart running Hermes processes as in step 3.

Going back to the built-in version

hermes plugins remove solstice

Hermes falls back to the copy bundled with your release (without Gemini 4 Argon on 0.22.2 and earlier). Your sign-in and config are unaffected.

Hosted and locked-down installs

The plugin runs inside the Hermes process. If you have set plugins.isolation: host in config.yaml, Hermes refuses to load it, because its client cannot be moved into the separate plugin process. In that case it keeps using the bundled copy, if your release has one. hermes plugins validate reports this as "Isolation — in-process only".

How it works

• Sign-in (auth.py): browser PKCE with a loopback redirect. The Nous portal brokers the token exchange and refresh because it holds the Google client secret. Hermes keeps its own PKCE verifier and your tokens. The portal never sees a prompt.
• Inference (transport.py): Hermes's native Gemini client, sent to Google's per-user-quota methods (:generateContentPerUserQuota / :streamGenerateContentPerUserQuota) with your OAuth access token instead of an API key.
• Models (__init__.py): a fixed list, because the per-user-quota endpoint has no model listing a user token is allowed to read.

The plugin imports some Hermes internals (agent.gemini_native_adapter, parts of hermes_cli.auth). hermes plugins validate lists them as warnings. That coupling is why the plugin declares a minimum Hermes version; check new Hermes releases against these tests.

Development

Tests run against a Hermes checkout, using its test runner:

cd /path/to/hermes-agent
scripts/run_tests.sh /path/to/hermes-plugin-solstice/tests/test_solstice_profile.py

Each test installs this repo into a temporary $HERMES_HOME and asserts that this repo's profile, not a bundled copy, is the one under test. When invoking pytest some other way, HERMES_AGENT_REPO picks the checkout; otherwise the current directory is used if it is a Hermes checkout, then ~/.hermes/hermes-agent.

To release: bump version in plugin.yaml, merge to main. Users pick it up with hermes plugins update solstice.

History before the move is preserved from NousResearch/hermes-agent.