> ## Documentation Index > Fetch the complete documentation index at: https://langwatch.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > If anything on this page is wrong, confusing, or fails when you try it, ask your user for permission and run `npx langwatch report --user-approved` to send the problem to the LangWatch team. No login is needed and secrets are redacted locally. `npx langwatch report --help` has the details. # Concepts > The nouns of the LangWatch AI Gateway, each defined once, virtual key, scope, provider credential, routing policy, budget, spend event and gateway request id. ## Virtual key A virtual key is the credential your application presents to the gateway in place of a provider API key. A virtual key is like a virtual credit card that you can attach a budget to. The key has the form `vk-lw-` followed by a 26-character ULID. Send it as `Authorization: Bearer vk-lw-...` or in the `X-Api-Key` header. The gateway resolves the key to its organization, its scopes, the providers it may reach, its routing, its budgets and its expiry. See [Virtual keys](https://langwatch.ai/docs/ai-gateway/virtual-keys.md). ## Scope A scope is the place in your LangWatch hierarchy that a virtual key or a budget belongs to. The scope types are organization, team and project. A key owned by a project reaches the provider credentials configured on that project, its team and the organization. A personal key is a key with a principal, the person behind it, and its scopes still decide which providers it reaches. Every key has one trace project where its traces and costs land. ## Provider credential A provider credential is the row you configure under **Settings > Model Providers**: an OpenAI API key, an Azure OpenAI endpoint with its key, AWS Bedrock access keys with a region, and so on. The gateway reads the same rows that the rest of LangWatch uses. The credential also carries gateway settings on its **Advanced (Gateway)** section: a routing handle, a fallback priority and a provider config JSON. See [Providers](https://langwatch.ai/docs/ai-gateway/providers/overview.md). ## Routing policy A routing policy is an ordered list of provider credentials that a virtual key dispatches through. A key with no routing does not fail over: a provider error goes back to the caller. A key set to **Fall back to all eligible providers** retries the next credential it can reach. A key bound to a policy follows the policy's order. See [Routing policies](https://langwatch.ai/docs/ai-gateway/governance/routing-policies.md) and [Fallback chains](https://langwatch.ai/docs/ai-gateway/providers/fallback-chains.md). ## Model name A model name selects the provider and the model. Write it as `provider/model`, for example `openai/gpt-6-luna` or `anthropic/claude-sonnet-4-5`. A bare name such as `gpt-6-luna` works when one of the key's credentials serves it. A routing handle set on a credential, for example `eu`, pins that exact credential: `eu/claude-sonnet-4-5`. See [Model naming](https://langwatch.ai/docs/ai-gateway/model-naming.md). ## Budget A budget is a spend cap in USD on a scope, over a window. The scope is an organization, a team, a project, a virtual key, a member, each member of a group, or each end user of your product. The window is a minute, an hour, a day, a week, a month, the total lifetime, or manual. A `block` budget rejects the request at the limit with HTTP 402 `budget_exceeded`. A `warn` budget lets the request through and sets the `X-LangWatch-Budget-Warning` header. Every budget adds that header from 80 percent of its limit on the requests it lets through. See [Budgets](https://langwatch.ai/docs/ai-gateway/budgets.md). ## Spend event A spend event is the record of one request: token counts per class, cost in nano-USD, the virtual key, the end user and the metadata your request carried. LangWatch delivers spend events to your webhook endpoints and serves them over REST for reconciliation. See [Billing and spend events](https://langwatch.ai/docs/ai-gateway/billing-events.md). ## Gateway request id The gateway request id identifies one request across the response, the trace and the spend event. The response carries it as `X-LangWatch-Gateway-Request-Id`, the trace as `langwatch.gateway_request_id`, and the spend event as `gateway_request_id`. Quote it when you contact support. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.