Providers, models, and routes
An execution route is eight things, not one. Knowing them is how you control cost and behaviour.
"Which model ran this?" is rarely one question. Harmony treats the full path as an execution route, and most cost and behaviour surprises come from a route element you were not tracking.
The shape of a route
The eight elements
| Element | Meaning |
|---|---|
| Harness | The agent program being driven |
| Provider | The vendor behind it |
| Account | Which of your identities with that provider |
| Model | The specific model requested |
| Effort | Reasoning depth, where the provider exposes it |
| Tool set | What the agent is permitted to call |
| Platform | Where the process runs |
| Billing class | Whose money is spent, under which plan |
Two steps of the same plan can differ in any of these.
Why the route is shown before consent
A route displayed before a run is a route you can refuse. This is why orchestration shows the chosen model per step with a stated reason, along with projected cost and billing route.
IMPORTANT
If projected cost or billing route cannot be determined, a run should block rather than proceed. Consent to spend you cannot see is not consent.
What Harmony knows, and what it does not
| Fact | Observable by Harmony? |
|---|---|
| Provider binary exists and resolves | Yes |
| Detected version | Yes |
| You are authenticated | No |
| Your plan tier | No |
| Remaining quota | No |
| Rate-limit state | No |
Harmony does not hold your provider credentials, so it cannot report your login state or entitlements — and it does not guess them. See account and authentication.
Changing the route
In the TUI:
/provider
/model
/profile
Changing route mid-session is legitimate and consequential: later turns in the same transcript can behave differently from earlier ones. When comparing outputs, check the route before concluding the model changed its mind.
Billing
Everything you spend goes to the provider whose plan you used, under that provider's pricing. Harmony is free to use and does not mark up inference. There is no background usage — a turn happens because you started one.
NOTE
"Free" refers to Harmony itself. Your provider subscriptions and API keys are unaffected, and they are what you are actually spending.
Custom providers
If you run an agent CLI that is not in the registry, you can define it yourself. The registry is a list of providers Harmony knows how to launch, not a limit on what it can launch.
The generated list of recognised ids is at provider registry.
Do not treat model rankings as universal
Which model is "best" depends on the task, the repository, and the route. Harmony does not publish anecdotal rankings as fact, and neither should your team's internal docs.