Wire the LLM provider

Bifrost is Harbor's LLM driver — one wire surface that speaks many providers. You don't change Go code to swap providers; you change the llm: block in harbor.yaml. This skill walks the four common postures + the dev-mock escape hatch + the model_profiles block the planner needs for context budgeting.

1. The four canonical postures

Posture A — OpenRouter (aggregator, easiest start)

llm:
  driver: bifrost
  provider: openrouter
  model: anthropic/claude-haiku-4.5
  api_key: env.OPENROUTER_API_KEY
  timeout: 60s
  model_profiles:
    anthropic/claude-haiku-4.5:
      context_window_tokens: 200000

OpenRouter aggregates 100+ models behind one API key. Best for prototyping ("does this model work for my agent?") and for production agents that want provider failover without bespoke wiring. Pricing is per-token, slightly above raw provider list price. Get a key at openrouter.ai.

Posture B — Anthropic direct

llm:
  driver: bifrost
  provider: anthropic
  model: claude-haiku-4.5
  api_key: env.ANTHROPIC_API_KEY
  timeout: 60s
  model_profiles:
    claude-haiku-4.5:
      context_window_tokens: 200000

Direct API access — usually cheapest per-token + lowest latency. Best when you've committed to Anthropic. Get a key at console.anthropic.com.

Posture C — OpenAI direct

llm:
  driver: bifrost
  provider: openai
  model: gpt-4.1-mini
  api_key: env.OPENAI_API_KEY
  timeout: 60s
  model_profiles:
    gpt-4.1-mini:
      context_window_tokens: 1000000

Same posture for OpenAI's API. Get a key at platform.openai.com.

Posture D — Custom OpenAI-compatible endpoint (NIM, vLLM, ollama, …)

llm:
  driver: bifrost
  provider: nim
  model: nvidia/nemotron-3-super
  timeout: 60s
  custom_providers:
    - name: nim
      base_url: https://integrate.api.nvidia.com/v1
      api_key_env_var: NVIDIA_API_KEY
      models: [nvidia/nemotron-3-super]
  model_profiles:
    nvidia/nemotron-3-super:
      context_window_tokens: 128000

For any provider that exposes an OpenAI-compatible endpoint — NVIDIA NIM, vLLM serving, ollama for local LLMs, Together AI, Anyscale, Groq, Mistral, Cohere, Bedrock-compatible gateways. The custom_providers block tells Bifrost how to reach it; the provider: field references the name. Multiple custom providers can coexist — pick one as the active provider:, register the others for swap.

2. model_profiles — the budgeting contract

model_profiles.<model>.context_window_tokens is what the planner consults when it decides how much memory to replay, how much tool output to inline, and when to clip. A profile for your llm.model is effectively REQUIRED: a model with no model_profiles entry has no context-window number, so the first LLM call hard-fails with ErrUnsupportedModel — there is no silent fallback. Give every model you actually use a profile:

model_profiles:
  anthropic/claude-haiku-4.5:
    context_window_tokens: 200000
  anthropic/claude-sonnet-4.5:
    context_window_tokens: 200000
  gpt-4.1-mini:
    context_window_tokens: 1000000

Look up the official context-window number from the provider's docs; never guess.

Future fields (post-V1.1) will let you set per-model output_max_tokens, pricing_per_input_token, and pricing_per_output_token. For V1.1, only context_window_tokens is honoured.

3. The dev-mock escape hatch

CLAUDE.md §13 forbids stub LLMs as production defaults. The boot path is fail-loud: no key set, no provider configured, the binary exits with ErrMissingAPIKey. There IS a documented escape hatch for first-clone convenience and CI smoke:

HARBOR_DEV_ALLOW_MOCK=1 harbor dev

When HARBOR_DEV_ALLOW_MOCK=1 is set, the binary boots with a deterministic stub LLM and prints a stderr banner on every boot:

[DEV-ONLY MOCK LLM — DO NOT USE IN PRODUCTION]

The banner is unmissable — it's bright, it's printed on every request to the LLM endpoint, and it's gated by a single env var. Production deployments NEVER set this var; CI smoke runs do, so we don't burn provider tokens validating the boot path. The flag does NOT degrade silently — a production.yaml with a misconfigured key + HARBOR_DEV_ALLOW_MOCK=0 (the default) is still a fail-loud exit.

4. Swap models without redeploying

Models are hot-reloadable. With harbor dev running:

1. Edit harbor.yaml, change llm.model: (and add the matching model_profiles entry).
2. Save.
3. harbor dev's fsnotify watcher drains in-flight runs, re-reads the config, re-binds Bifrost to the new model, and accepts new runs.

You see this in the runtime stderr:

time=... msg="config reload: llm.model changed" old=claude-haiku-4.5 new=claude-sonnet-4.5

The Console's connection footer reflects the new model on the next Task run.

Provider swap (e.g. OpenRouter → Anthropic direct) is the same flow — edit, save, watcher reloads. Bifrost handles the provider handshake internally.

5. Timeouts + retries

llm:
  # ... provider + model ...
  timeout: 60s                  # request-level timeout
  network_defaults:             # applies to every provider (native + custom)
    max_retries: 2              # extra attempts after the first try
    retry_backoff_initial: 1s   # backoff before the first retry
    retry_backoff_max: 8s       # backoff ceiling
  model_profiles:
    anthropic/claude-haiku-4.5:
      context_window_tokens: 200000
      max_retries: 4            # per-model override of network_defaults.max_retries

network_defaults sets the retry policy for every provider; a model_profiles.<model>.max_retries entry overrides it for that one model. The retry policy is per-attempt; the timeout applies to each individual attempt. Backoff grows from retry_backoff_initial up to the retry_backoff_max ceiling. Omit any field and it falls through to Bifrost's package-level default. Bifrost honours Retry-After headers from the provider when present.

Long-running models (deep reasoning, large context) sometimes exceed the default 60s; bump to 120s or 240s for those. The Console's Task page surfaces timeout errors with the provider's verbatim response, so you can tune fast.

6. Embeddings are a separate block (not an llm knob)

Harbor's embedding client is a sibling seam to the chat client — turning text into vectors gets its own provider/model/key, configured at the top-level embeddings: block, never inherited from llm.*:

embeddings:
  driver: bifrost                  # the default; omit freely
  provider: openai
  model: text-embedding-3-small
  api_key: env.OPENAI_API_KEY      # same env.NAME convention as llm.api_key
  # dimensions: 256                # optional reduced output dimension

You only need it when something consumes embeddings — the opt-in semantic retrieval modes (memory.retrieval: semantic / skills.retrieval: semantic; see configure-memory-and-skills) or your own à-la-carte retrieval (docs/recipes/embed-and-retrieve.md). Enabling a semantic mode without the block fails validation loudly naming the missing keys; there is no mock embeddings driver and no fallback to the chat provider.

Common failure modes

• harbor dev exits immediately with ErrMissingAPIKey: env.OPENROUTER_API_KEY not set. Source your .env or export the var in the shell that ran harbor dev. Verify with echo $OPENROUTER_API_KEY.
• harbor dev exits with ErrUnknownProvider: "nim". You set provider: nim but forgot the matching custom_providers: entry. Add it.
• Every LLM call times out. Either your timeout: is too low for the model, OR the provider is unreachable from the runtime's network. Check with a curl https://api.openrouter.ai/v1/models from the runtime host first.
• llm.context_leak events fire mid-run. A tool returned >32KB inline instead of an ArtifactStub. See add-an-in-process-tool §4.
• harbor dev fails the first LLM call with ErrUnsupportedModel: model has no configured ModelProfile. Your llm.model has no model_profiles.<model> entry, so the runtime has no context-window number for it and refuses the call — there is no fallback. Add the model_profiles.<model>.context_window_tokens entry.

See also

• define-the-agent-yaml — the llm: block in the context of the full yaml.
• configure-memory-and-skills — memory budgeting against the context window.
• observe-with-the-console — the LLM tab in the Console's Task page shows every prompt/completion.
• Bifrost's full provider matrix: github.com/maximhq/bifrost.
• The CONFIG.md reference: docs/CONFIG.md#llm (and #embeddings for the embedding client).