hermes-agent/website/docs/developer-guide/model-provider-plugin.md

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10	Model Provider Plugins	How to build a model provider (inference backend) plugin for Hermes Agent

Building a Model Provider Plugin

Model provider plugins declare an inference backend — an OpenAI-compatible endpoint, an Anthropic Messages server, a Codex-style Responses API, or a Bedrock-native surface — that Hermes can route AIAgent calls through. Every built-in provider (OpenRouter, Anthropic, GMI, DeepSeek, Nvidia, …) ships as one of these plugins. Third parties can add their own by dropping a directory under $HERMES_HOME/plugins/model-providers/ with zero changes to the repo.

:::tip Model provider plugins are the third kind of provider plugin. The others are Memory Provider Plugins (cross-session knowledge) and Context Engine Plugins (context compression strategies). All three follow the same "drop a directory, declare a profile, no repo edits" pattern. :::

How discovery works

providers/__init__.py._discover_providers() runs lazily the first time any code calls get_provider_profile() or list_providers(). Discovery order:

1. Bundled plugins — <repo>/plugins/model-providers/<name>/ — ship with Hermes
2. User plugins — $HERMES_HOME/plugins/model-providers/<name>/ — drop in a directory; restart an already-running Hermes process to discover it
3. Installed plugins — $HERMES_HOME/plugins/<name>/ (where hermes plugins install owner/repo clones) — imported only when plugin.yaml declares kind: model-provider; every other kind there belongs to the general PluginManager
4. Legacy single-file — <repo>/providers/<name>.py — back-compat for out-of-tree editable installs

User plugins override bundled plugins of the same name because register_provider() is last-writer-wins. Drop a $HERMES_HOME/plugins/model-providers/gmi/ directory to replace the built-in GMI profile without touching the repo.

Directory structure

plugins/model-providers/my-provider/
├── __init__.py       # Calls register_provider(profile) at module-level
├── plugin.yaml       # kind: model-provider + metadata (optional but recommended)
└── README.md         # Setup instructions (optional)

The only required file is __init__.py. plugin.yaml is used by hermes plugins for introspection and by the general PluginManager to route the plugin to the right loader; without it, the general loader falls back to a source-text heuristic.

Minimal example — a simple API-key provider

# plugins/model-providers/acme-inference/__init__.py
from providers import register_provider
from providers.base import ProviderProfile

acme = ProviderProfile(
    name="acme-inference",
    aliases=("acme",),
    display_name="Acme Inference",
    description="Acme — OpenAI-compatible direct API",
    signup_url="https://acme.example.com/keys",
    env_vars=("ACME_API_KEY", "ACME_BASE_URL"),
    base_url="https://api.acme.example.com/v1",
    auth_type="api_key",
    default_aux_model="acme-small-fast",
    fallback_models=(
        "acme-large-v3",
        "acme-medium-v3",
        "acme-small-fast",
    ),
)

register_provider(acme)

# plugins/model-providers/acme-inference/plugin.yaml
name: acme-inference
kind: model-provider
version: 1.0.0
description: Acme Inference — OpenAI-compatible direct API
author: Your Name

That's it. After dropping these two files, the following auto-wire with no other edits:

Integration	Where	What it gets
Credential resolution	hermes_cli/auth.py	PROVIDER_REGISTRY["acme-inference"] populated from profile
--provider CLI flag	hermes_cli/main.py	Accepts acme-inference
/model --provider, model picker switch	hermes_cli/providers.py::resolve_provider_full	Resolves acme-inference and every alias to the profile (switch lands on name, so acme persists as acme-inference); user providers: / custom_providers: blocks keep precedence. A profile with an empty base_url (endpoint minted at runtime) resolves too, on the last rung
hermes model picker	hermes_cli/models.py	Appears in CANONICAL_PROVIDERS, model list fetched from {base_url}/models
hermes doctor	hermes_cli/doctor.py	Health check for ACME_API_KEY + {base_url}/models probe
hermes setup	hermes_cli/config.py	ACME_API_KEY appears in OPTIONAL_ENV_VARS and the setup wizard
URL reverse-mapping	agent/model_metadata.py	Hostname → provider name for auto-detection
Auxiliary model	agent/auxiliary_client.py	Uses default_aux_model for compression / summarization
Runtime resolution	hermes_cli/runtime_provider.py	Returns correct base_url, api_key, api_mode
Transport	agent/transports/chat_completions.py	Profile path generates kwargs via prepare_messages / build_extra_body / build_api_kwargs_extras

ProviderProfile fields

Full definition in providers/base.py. The most useful ones:

Field	Type	Purpose
name	str	Canonical id — matches model.provider in config.yaml and the --provider flag
aliases	tuple[str, ...]	Alternative names resolved by get_provider_profile() (e.g. grok → xai)
api_mode	str	chat_completions | codex_responses | anthropic_messages | bedrock_converse
display_name	str	Human label shown in hermes model picker
description	str	Picker subtitle
signup_url	str	Shown during first-run setup ("get an API key here")
env_vars	tuple[str, ...]	API-key env vars in priority order; a final *_BASE_URL entry is used as the user base-URL override
base_url	str	Default inference endpoint
models_url	str	Explicit catalog URL (falls back to {base_url}/models)
auth_type	str	api_key | oauth_device_code | oauth_external | copilot | aws_sdk | external_process
auth_handler	Callable | None	Provider-owned hermes auth add/status/logout/refresh <name> — see Provider-owned auth
refresh_credential	Callable | None	Provider-owned rotation of a pooled OAuth row — same section
classify_api_error	Callable | None	Provider-scoped error-classification override — see Recovery and error classification
fallback_models	tuple[str, ...]	Curated list shown when live catalog fetch fails — in the /model picker AND the first-time hermes setup / hermes model API-key flow, which resolve the catalog the same way (fetch_models() merged curated-first with fallback_models; fallback_models alone when the fetch returns None or raises)
supports_vision	bool	Declares the provider's API accepts image content inside tool-result messages (a provider-wide wire capability). Per-model user-image routing comes from model_capabilities / models.dev, not from this flag
model_capabilities	dict[str, dict[str, Any]]	Per-model capability declarations in the model_overrides schema — see Declaring model capabilities
default_headers	dict[str, str]	Sent on every request (e.g. Copilot's Editor-Version); also forwarded by the default fetch_models() catalog request
fixed_temperature	Any	None = use caller's value; OMIT_TEMPERATURE sentinel = don't send temperature at all (Kimi)
default_max_tokens	int | None	Provider-level max_tokens cap (Nvidia: 16384)
unsupported_response_formats	tuple	response_format types the API rejects outright; auxiliary requests omit them instead of paying a guaranteed 400 (DeepSeek: ("json_schema",))
default_aux_model	str	Cheap model for auxiliary tasks (compression, vision, summarization)

Declaring model capabilities

Hermes resolves per-model capabilities (supports_reasoning, supports_vision, supports_tools, context_window) from the models.dev catalog, which does not know an out-of-tree provider's models. Declare them once on the profile:

register_provider(ProviderProfile(
    name="acme",
    auth_type="api_key",
    env_vars=("ACME_API_KEY",),
    base_url="https://api.acme.example/v1",
    fallback_models=("acme-large-high", "acme-small"),
    model_capabilities={
        "acme-large-high": {
            "supports_reasoning": False,   # reasoning tier is fixed by the model id
            "supports_vision": True,
            "supports_tools": True,
            "context_window": 64000,
            "model_family": "acme",
        },
    },
))

Keys are exact model IDs. Values use the model_overrides schema from config.yaml — the three capability booleans, a positive context_window, an optional model_family — and omitted fields stay unknown (not False), so a partial entry patches catalog metadata without erasing it.

One declaration feeds every consumer that reads the catalog through agent.models_dev: the /model picker's reasoning badge, image routing (decide_image_input_mode goes native for a supports_vision: True model even when the profile-wide supports_vision is unset), context-window lookup, and the dashboard's /api/model/info. Precedence: explicit user model_overrides.<provider>.<model> → plugin declaration → catalog → fill-gap _default. Models the plugin does not declare keep the catalog/heuristic path.

Not covered: the picker's fast badge (a model-name heuristic in hermes_cli/models.py::model_supports_fast_mode), reasoning-effort vocabulary (agent/reasoning_effort.py), and transport request fields. Declarations do not add models to a picker — use fallback_models / fetch_models for that. The registry is discovered once per process: restart Hermes after editing them.

Overridable hooks

Subclass ProviderProfile for non-trivial quirks:

from typing import Any
from providers.base import ProviderProfile

class AcmeProfile(ProviderProfile):
    def prepare_messages(self, messages: list[dict[str, Any]]) -> list[dict[str, Any]]:
        """Provider-specific message preprocessing. Runs after codex
        sanitization, before developer-role swap. Default: pass-through."""
        # Example: Qwen normalizes plain-text content to a list-of-parts
        # array and injects cache_control; Kimi rewrites tool-call JSON
        return messages

    def build_extra_body(self, *, session_id=None, **context) -> dict:
        """Provider-specific extra_body fields merged into the API call.
        Context includes: session_id, provider_preferences, model, base_url,
        reasoning_config. Default: empty dict."""
        # Example: OpenRouter's provider-preferences block,
        # Gemini's thinking_config translation.
        return {}

    def build_api_kwargs_extras(self, *, reasoning_config=None, **context):
        """Returns (extra_body_additions, top_level_kwargs). Needed when some
        fields go top-level (Kimi's reasoning_effort, OpenRouter's verbosity for
        adaptive Anthropic models) and some go in extra_body (OpenRouter's
        reasoning dict). Default: ({}, {})."""
        return {}, {}

    def fetch_models(self, *, api_key=None, base_url=None, timeout=8.0) -> list[str] | None:
        """Live catalog fetch. Default hits {models_url or base_url}/models with
        Bearer auth. Override for: custom auth (Anthropic), no REST endpoint
        (Bedrock → None), or public/unauthenticated catalogs (OpenRouter)."""
        return super().fetch_models(api_key=api_key, base_url=base_url, timeout=timeout)

    def fetch_account_usage(self, *, api_key=None, base_url=None):
        """Return AccountUsageSnapshot for /usage, or None when unavailable.

        The hook runs only when the provider has no built-in usage fetcher.
        It may raise: core catches failures and keeps /usage empty for that turn.
        """
        return None

    def create_client(self, **client_kwargs):
        """Supply your own client object instead of the shared openai.OpenAI.
        Default returns None (= use the standard client). Override when the
        wire protocol is not OpenAI-over-HTTP — e.g. an ACP subprocess shim.
        client_kwargs is what the core would have passed to openai.OpenAI
        (api_key, base_url, command, args, timeouts, headers…); accept **kwargs
        and pick what you need. A raise is logged and falls back to the
        standard client."""
        return None

Account usage

Model-provider plugins can provide account or plan usage to /usage by overriding ProviderProfile.fetch_account_usage. Import and return the shared agent.account_usage.AccountUsageSnapshot (with any AccountUsageWindow entries); do not format output in the plugin. Returning None, or raising an exception, leaves /usage empty just as it does for providers without usage data. Built-in usage fetchers always take precedence, so this hook cannot replace the account-usage behavior for a built-in provider. The hook runs under a shared 10 s deadline (agent.account_usage.PLUGIN_USAGE_HOOK_DEADLINE_S) on every surface; overrunning it renders nothing for that turn rather than stalling /usage, so give your own HTTP calls a shorter timeout.

The bundled plugins/model-providers/opencode-zen/ profile implements this hook for the OpenCode Go plan windows; every /usage surface (CLI hermes usage and /usage, the messaging gateway, the TUI/Desktop usage feed) renders the snapshot through the same core formatter.

from datetime import datetime, timezone

from agent.account_usage import AccountUsageSnapshot, AccountUsageWindow

def fetch_account_usage(self, *, api_key=None, base_url=None):
    return AccountUsageSnapshot(
        provider=self.name,
        source="my_provider_api",
        fetched_at=datetime.now(timezone.utc),
        windows=(AccountUsageWindow(label="Monthly", used_percent=25),),
    )

External-process (ACP) providers

An agent CLI driven over stdio is not an HTTP endpoint. Set auth_type="external_process", describe how to launch the binary, and supply the client with create_client. No core edits are needed — hermes -m <name>, /model, credential resolution, runtime resolution and the auxiliary client (compression, vision) all key on auth_type, not on the provider name. plugins/model-providers/copilot-acp/ is the in-tree example.

Field	Purpose
process_command	Default binary, e.g. "copilot"
process_args	Default argv tail, e.g. ("--acp", "--stdio")
process_command_env_vars	Env vars that override the binary, checked in order
process_args_env_var	Env var that overrides argv (shlex-split)

The client your create_client returns receives command and args in client_kwargs. If it is already complete and async-safe, declare HERMES_SKIP_TRANSPORT_WRAP = True / HERMES_SKIP_ASYNC_WRAP = True as class attributes so the auxiliary client does not re-dispatch it through an HTTP wire adapter.

Picker rows for non-api-key plugins

Every registered profile joins CANONICAL_PROVIDERS by slug (a plugin re-declaring a built-in slug such as bedrock is deduped, never doubled), so external-process and OAuth plugins appear in hermes model, /model and the Desktop model selector alongside copilot-acp. Visibility is gated by credentials, not by auth_type:

auth_type	Row is listed / authenticated when	Model list
external_process	the binary resolves (process_command or one of process_command_env_vars is on PATH), or base_url is acp+tcp://… — the same structural gate hermes auth status reports. A resolving binary is also the sign-in evidence (auth_verified) the Desktop model selector's explicit-only filter uses, so the row shows there like the bundled ACP provider does	fetch_models() (your subprocess probe), else fallback_models
oauth_external / oauth_device_code	the credential pool holds a row for the slug with a live (non-expired) token — hermes auth status <name> and list_available_providers().authenticated both read the pool; an expired row with refresh_token and a refresh_credential hook reports needs_refresh	fetch_models() with the pooled token, else fallback_models (declare at least one)

The catalog cache is keyed on the profile's process_command_env_vars / process_args_env_var values, so pointing HERMES_<X>_COMMAND at a different binary re-discovers models. Executable discovery is not a login check: an unauthenticated CLI still lists, and the subprocess reports the failure at first use.

Selecting the row in hermes model (and the setup wizard) runs one generic flow keyed by the profile's auth_type: external-process profiles are launch-checked (resolve_external_process_provider_credentials), OAuth profiles need a live pool row (otherwise the flow prints hermes auth add <name> and stops), then the merged catalog is offered and config.model is persisted with the profile's base_url/api_mode. No _model_flow_* entry in core is needed.

Hook reference examples

Look at these bundled plugins for idioms:

Plugin	Why look
plugins/model-providers/openrouter/	Aggregator with provider preferences, public model catalog
plugins/model-providers/gemini/	thinking_config translation (native + OpenAI-compat nested forms)
plugins/model-providers/kimi-coding/	OMIT_TEMPERATURE, extra_body.thinking, top-level reasoning_effort
plugins/model-providers/qwen-oauth/	Message normalization, cache_control injection, VL high-res
plugins/model-providers/nous/	Attribution tags, "omit reasoning when disabled"
plugins/model-providers/custom/	Ollama num_ctx + think: false quirks
plugins/model-providers/bedrock/	api_mode="bedrock_converse", fetch_models returns None (no REST endpoint)

User overrides — replace a built-in without editing the repo

Say you want to point gmi at your private staging endpoint for testing. Create ~/.hermes/plugins/model-providers/gmi/__init__.py:

from providers import register_provider
from providers.base import ProviderProfile

register_provider(ProviderProfile(
    name="gmi",
    aliases=("gmi-cloud", "gmicloud"),
    env_vars=("GMI_API_KEY",),
    base_url="https://gmi-staging.internal.example.com/v1",
    auth_type="api_key",
    default_aux_model="google/gemini-3.1-flash-lite-preview",
))

In a fresh Hermes process, get_provider_profile("gmi").base_url returns the staging URL. No repo patch, no rebuild. Because user plugins are discovered after bundled ones, the user register_provider() call wins.

The override also reaches the runtime. Built-in providers have a row in hermes_cli.auth.PROVIDER_REGISTRY (the table resolve_runtime_provider() reads its endpoint and env vars from); a $HERMES_HOME plugin re-registering that name rewrites the row's profile-derived fields, so inference goes to the staging URL, not the bundled one:

Profile field	Registry row field	When
base_url	inference_base_url	profile sets a non-empty base_url
env_vars (non-URL entries)	api_key_env_vars	api-key row and profile sets env_vars
env_vars (final *_BASE_URL / *_URL entry)	base_url_env_var	profile declares one; otherwise the built-in env var (e.g. GMI_BASE_URL) stays

Only a user plugin ($HERMES_HOME/plugins/model-providers/ or an installed kind: model-provider plugin) triggers this; a bundled profile never rewrites a built-in row, and copilot, kimi-coding, kimi-coding-cn and zai keep their bespoke credential resolution. A field the profile leaves empty keeps the built-in value. A *_BASE_URL env var still wins over both.

api_mode selection

Four values are recognized. Hermes picks one based on:

1. User explicit override (config.yaml model.api_mode when set)
2. OpenCode's per-model dispatch (opencode_model_api_mode for Zen and Go)
3. URL auto-detection — /anthropic suffix → anthropic_messages, api.openai.com → codex_responses, api.x.ai → codex_responses, /coding on Kimi domains → chat_completions
4. Profile api_mode as a fallback when URL detection finds nothing
5. Default chat_completions

Set profile.api_mode to match the default your provider ships — it acts as a hint. User URL overrides still win.

Auth types

auth_type	Meaning	Who uses it
api_key	Single env var carries a static API key	Most providers
oauth_device_code	Device-code OAuth flow	Nous Portal; out-of-tree plugins via auth_handler
oauth_external	User signs in elsewhere, tokens land in auth.json	Anthropic OAuth, MiniMax OAuth, Qwen Portal, Nous Portal
copilot	GitHub Copilot token refresh cycle	copilot plugin only
aws_sdk	AWS SDK credential chain (IAM role, profile, env)	bedrock plugin only
external_process	Auth handled by a subprocess the agent spawns (see External-process providers)	copilot-acp plugin, out-of-tree ACP plugins

Every profile is mirrored into Hermes' auth registry under the auth_type it declares (two exclusions: an api_key profile with empty env_vars, and the aggregator/user-supplied slugs openrouter/custom plus the bespoke-refresh built-ins copilot/kimi-coding/zai), so hermes auth, --provider <name> and runtime resolution accept it whatever its shape. What differs is who performs the login: api_key profiles get the built-in key prompt / env-var resolution; every other auth_type is provider-owned — the plugin ships the two hooks below, and a non-api-key profile without an auth_handler makes hermes auth add <name> fail with a clear "ships no auth_handler" error instead of silently doing nothing.

Provider-owned auth (auth_handler, refresh_credential)

auth_type describes what kind of credential a provider needs; auth_handler is how the plugin acquires it — its own device-code / OIDC / IdC flow inside the existing hermes auth command family (model-provider manifests are skipped by the generic command-plugin loader, so register(ctx) is not the way to add commands). refresh_credential is how the credential pool rotates a pooled token the plugin stored.

import uuid
from providers import register_provider
from providers.base import ProviderProfile


def example_auth(action: str, args) -> bool:
    """action: "add" | "status" | "logout" | "refresh"; args: parsed CLI namespace."""
    if action == "add":
        from agent.credential_pool import AUTH_TYPE_OAUTH, PooledCredential, load_pool
        tokens = run_device_code_flow()                      # provider-specific
        load_pool("example-oauth").add_entry(PooledCredential(
            provider="example-oauth", id=uuid.uuid4().hex[:6], label=tokens["account"],
            auth_type=AUTH_TYPE_OAUTH, priority=0, source="manual:example_device",
            access_token=tokens["access_token"], refresh_token=tokens["refresh_token"],
            extra={"tenant": tokens["tenant"]}))             # any extra keys round-trip through auth.json
        print("Signed in to Example.")
        return True
    if action == "status":
        print("example-oauth: " + ("logged in" if load_pool("example-oauth").entries() else "logged out"))
        return True
    return False   # decline → this action stays with the built-in credential-pool handling


def example_refresh(entry):
    """Called by the credential pool with the pooled row; return the rotated values, None, or raise."""
    tokens = post_refresh(entry.refresh_token)          # the raw token-endpoint response is fine as-is
    return {"access_token": tokens["access_token"], "refresh_token": tokens["refresh_token"],
            "expires_at_ms": tokens["expires_at_ms"], "expires_in": tokens["expires_in"]}


register_provider(ProviderProfile(
    name="example-oauth", auth_type="oauth_external", base_url="https://api.example.com/v1",
    auth_handler=example_auth, refresh_credential=example_refresh))

Contract
auth_handler(action, args)	args is the parsed hermes auth namespace for CLI actions; the interactive setup picker passes a minimal namespace carrying only provider, so read options with getattr(args, name, None). Truthy = handled (Hermes prints nothing more, exit 0); falsy = fall back to the built-in path for that action. An exception becomes SystemExit("<provider> auth handler failed for <action>: …").
refresh_credential(entry)	Receives the PooledCredential; returns a mapping of rotated values or None. Keys that are PooledCredential fields (access_token, refresh_token, expires_at_ms, …) replace the row's fields; every other key (expires_in, token_type, scope — the raw token-endpoint shape) lands in entry.extra and round-trips through auth.json. Returning None/an empty mapping means the plugin could not rotate: the row is benched exactly like a failed refresh request (never reported as refreshed, so a dead bearer is not replayed). Its presence is what makes the provider refreshable — hermes auth refresh <name> and the main-loop 401 recovery call it through the pool with no core name list involved; the auxiliary client's 401 recovery reaches it only for pooled rows it already treats as recoverable (api-key rows and the built-in OAuth routes).
Refresh failures	Raise hermes_cli.auth_constants.AuthError(..., relogin_required=True) (or with code invalid_grant / invalid_token / refresh_token_reused) when the grant is dead: the row goes DEAD, leaves rotation and Hermes logs a WARNING naming hermes auth add <name>. Any other exception (network, 429, 5xx) is transient — the row is benched for one cooldown and retried.
Concurrency	The hook runs under the shared auth.json lock. Before calling it the pool re-reads the row; if another Hermes process (gateway + CLI, two profiles) already rotated the pair, that pair is adopted and your hook is not called — safe for single-use refresh tokens. After the hook returns, the rotated row is written through to auth.json.
No hooks	api_key profiles behave exactly as before. Any other auth_type without auth_handler fails loud on hermes auth add.

hermes auth add|status|logout|refresh <provider> consults the handler first — before the built-in credential-pool flow. Registering the same name twice is last-writer-wins, so a user plugin can replace a bundled provider's flow.

Hermes passes the parsed namespace, not provider-declared flags: ask for provider-specific values interactively (or read your own config/env). Rows the plugin stores in the pool are its own — extra keys survive load → save → load, and Hermes passes no secrets beyond that pooled row to refresh_credential.

Declarative OAuth (PKCE) for plugins

A provider whose IdP speaks standard OAuth 2.0 Authorization Code + PKCE does not need to write the hooks above by hand: declare the endpoints in OAuthPKCEConfig and let the two factories build them.

from hermes_cli.auth_oauth_pkce_plugin import OAuthPKCEConfig, pkce_auth_handler, pkce_refresh_credential
from providers import register_provider
from providers.base import ProviderProfile

cfg = OAuthPKCEConfig(
    client_id="hermes-public-client",                       # public client — no secret, PKCE is the proof
    authorize_url="https://auth.example.com/oauth/authorize",
    token_url="https://auth.example.com/oauth/token",
    scopes=("inference", "offline_access"),
    redirect_port=0,                                        # 0 = OS-assigned; pin it if the IdP allowlists the URI
)

register_provider(ProviderProfile(
    name="example-pkce", auth_type="oauth_external", base_url="https://api.example.com/v1",
    auth_handler=pkce_auth_handler(cfg), refresh_credential=pkce_refresh_credential(cfg)))

Hermes then owns the whole lifecycle: hermes auth add example-pkce [--no-browser] opens the browser (or prints the URL, with the SSH-tunnel hint on a remote box), listens on http://127.0.0.1:<port>/callback, checks the CSRF state, exchanges the code with S256 PKCE and stores the grant as a pooled oauth credential (source: manual:loopback_pkce, expires_at_ms, refresh_token); auth status reports logged in / expired; auth logout removes the rows; auth refresh and the 401 recovery paths rotate via the refresh_token grant, re-reading auth.json under the auth lock first so a peer's rotation is adopted instead of spending a single-use refresh token twice.

Security boundary (enforced before any request, on login and refresh alike): both endpoints must be https:// (plain http:// is accepted only for a loopback-literal host — a local development IdP); the token_url host must be the authorize_url host or a subdomain of it (or listed in allowed_hosts); the listener binds the literal 127.0.0.1; tokens, state and the PKCE verifier are never logged. Optional fields: audience, extra_authorize_params, extra_token_params, redirect_path, timeout_seconds, label.

Recovery and error classification

A kind: model-provider plugin is loaded by provider discovery, not by the generic plugin manager, so the transform_api_error_classification plugin hook is not reachable from it without shipping a second plugin component. The profile carries the equivalent seam instead:

def classify(error, *, status_code, error_code, message, body, model):
    # A vendor-specific 403 that is a spent plan, not a bad credential.
    if status_code == 403 and error_code == "quota_exhausted":
        return {"reason": "billing", "retryable": False, "should_rotate_credential": True, "should_fallback": True}
    return None  # decline → built-in classification


register_provider(ProviderProfile(name="example-oauth", auth_type="oauth_external",
                                  base_url="https://api.example.com/v1",
                                  refresh_credential=example_refresh, classify_api_error=classify))

Contract
classify_api_error(error, *, status_code, error_code, message, body, model)	Consulted by agent.error_classifier.classify_api_error for failures of this provider only, after any generic transform_api_error_classification hooks and before the built-in pipeline. message is the lower-cased error text, body the parsed JSON body (may be empty). Return {"reason": <FailoverReason name>} plus optional retryable / should_compress / should_rotate_credential / should_fallback / error_context to override (for terminal reasons — billing, auth, model_not_found … — should_fallback: True implies retryable: False unless you set it, because the fallback chain only runs for non-retryable verdicts; rate-limit reasons keep the built-in retry-then-fallback shape); None (or an unknown reason) leaves the built-in verdict. Exceptions are swallowed and logged at DEBUG. The verdict drives the same recovery as for built-ins — e.g. billing benches the credential for the billing TTL instead of the transient 403 cooldown.
401 on a plugin credential	Handled by the credential pool, no core edit: the failing pooled row is refreshed through refresh_credential once per attempt (capped at two refreshes per row per session), the client is rebuilt with the rotated token and the request retried. A None/empty return or an exception benches the row — the request then rotates or falls to the generic "sign in again: hermes auth add <name>" copy, never to a built-in provider's guidance.
Auxiliary calls	Auxiliary-client 401s take the same pool refresh (try_refresh_current → refresh_credential).

Recovery that remains name-keyed in core is behaviour with no safe generic shape (a provider-specific token store to re-sync, a plan-tier entitlement wall, a single-use refresh-token quarantine). A plugin that needs one of those owns it inside refresh_credential / classify_api_error.

Discovery timing

Provider discovery is lazy — triggered by the first get_provider_profile() or list_providers() call in the process. In practice this happens early at startup (auth.py module load extends PROVIDER_REGISTRY eagerly). If you need to verify your plugin loaded, run:

hermes doctor

— a successful auth_type="api_key" profile appears under the Provider Connectivity section with a /models probe.

For programmatic inspection:

from providers import list_providers
for p in list_providers():
    print(p.name, p.base_url, p.api_mode)

Testing your plugin

Point HERMES_HOME at a temp directory so you don't pollute your real config:

export HERMES_HOME=$HOME/.hermes/cache/scratch/hermes-plugin-test
mkdir -p $HERMES_HOME/plugins/model-providers/my-provider
cat > $HERMES_HOME/plugins/model-providers/my-provider/__init__.py <<'EOF'
from providers import register_provider
from providers.base import ProviderProfile
register_provider(ProviderProfile(
    name="my-provider",
    env_vars=("MY_API_KEY",),
    base_url="https://api.my-provider.example.com/v1",
    auth_type="api_key",
))
EOF

export MY_API_KEY=your-test-key
hermes -z "hello" --provider my-provider -m some-model

General PluginManager integration

The general PluginManager (the thing hermes plugins operates on) sees model-provider plugins but does not import them — providers/__init__.py owns their lifecycle. The manager records the manifest for introspection and categorizes by kind: model-provider. When you drop an unlabeled user plugin into $HERMES_HOME/plugins/ that happens to call register_provider with a ProviderProfile, the manager auto-coerces it to kind: model-provider via a source-text heuristic — so the plugin still routes correctly even without plugin.yaml.

Distribute via pip

Model providers can ship as a pip package. Expose an entry point in the hermes_agent.plugins group in your pyproject.toml:

[project.entry-points."hermes_agent.plugins"]
acme-inference = "acme_hermes_plugin:register"

The target may be either:

• a callable (module:func) — invoked with no arguments; it should call register_provider(profile), or
• a bare module (module) — imported for its module-level register_provider(...) side effect, mirroring the directory-plugin __init__.py contract.

providers/__init__.py discovers these entry points itself — the general PluginManager never invokes provider registration for pip packages (its entry-point path targets register(ctx)-style general plugins, gated by plugins.enabled), so the provider registry does its own scan. Two rules apply:

• Opt-in required. The same plugins.enabled allow-list (and plugins.disabled deny-list) from config.yaml governs this scan. A pip package is never imported just because it is installed — users must add the entry-point name to plugins.enabled:

  plugins:
    enabled:
      - acme-inference
  

• Lowest precedence. Entry-point plugins are discovered before filesystem plugins: because register_provider() is last-writer-wins, a bundled or $HERMES_HOME profile of the same name always overrides a pip-installed one. A pip package can add a genuinely new provider, but cannot silently hijack a first-party provider name.

Targets that require arguments (a general plugin's register(ctx)) are skipped by the provider scan — they belong to the PluginManager. A broken entry point is isolated — it is logged at warning level and skipped, and never blocks discovery of the other providers.

See Building a Hermes Plugin for the full entry-points setup.

Related pages

• Provider Runtime — resolution precedence + where each layer reads the profile
• Adding Providers — end-to-end checklist for new inference backends (covers both the fast plugin path and the full CLI/auth integration)
• Memory Provider Plugins
• Context Engine Plugins
• Building a Hermes Plugin — general plugin authoring