> ## Documentation Index > Fetch the complete documentation index at: https://docs.lerian.studio/llms.txt > Use this file to discover all available pages before exploring further. # Read what one conversation cost, broken down by model > What this conversation has spent, one row per model it was billed under. The session resource already reports the same money as two scalars — `usage.costUsd` over the whole conversation, and `cacheSpend`, which DECOMPOSES part of that same figure rather than adding to it. This is the third view of those same dollars and adds nothing to them either: a conversation that ran on three models reports one number there and says which model spent it here, and the rows sum to that number. The model is the one a round was BILLED under, which is the model that answered and not the one that was asked for. A round this host cannot price contributes its tokens and no dollars, so its group reports costComplete false and its costUsd is a floor. A colleague refused the transcript is refused this. ## OpenAPI ````yaml /es/openapi/v3-current/narya.yaml get /v1/sessions/{sessionId}/usage openapi: 3.1.0 info: title: Narya Host API version: 1.0.0 description: >- The contract between the Narya host and every client. One long-lived host serves this API over a Unix socket in your Narya home. The terminal client and the one-shot command that Lerian ships drive this API, and a client you write drives the same one. Requests authenticate with a bearer token issued by the identity provider the host is configured with. An operation that declares another security scheme also accepts that credential. A request without a valid credential gets 401 with NRY-0011. A caller whose role lacks the permission an operation needs gets 403 with NRY-0028. Submitting a message returns 202 with a turn id. Everything the turn produces streams over GET /v1/events as server-sent events with a typed envelope, and a stream resumes from a Last-Event-ID header. One error envelope: code, title and message. Codes are NRY- followed by four digits. Cursors are opaque. servers: [] security: - bearerAuth: [] tags: - name: host description: The host process itself — version, uptime, mode, store. - name: sessions description: Durable conversation containers. Archive, never destroy. - name: messages description: Submitting work into a session and interrupting it. - name: events description: The server-sent event stream every client consumes. - name: lanes description: Parallel tracks inside a session — main, subagent, side. - name: agents description: Named recipes — instructions, tools, model, policy. Read-only in v1. - name: ladder description: >- What a person can type: the skills and command files in force for one repository, and expanding one into text. Five origins merged, nearest winning a name, the repository's own rungs gated on trust. - name: permissions description: Pending permission asks, decisions, and the decision audit. - name: intercom description: Sessions on one machine finding and messaging each other. - name: packages description: The one thing a user installs — resources, Go code, or both. - name: extensions description: >- Host-side extensions and the operations each exposes over the wire. This is the generic lane a host extension uses to serve its own client half (a TUI component, a web panel) or any API-only consumer, without adding routes to this contract. - name: workflows description: Deterministic multi-agent orchestration runs. - name: providers description: Model suppliers, their auth state, and the model catalogue. - name: monitors description: >- Long-running watchers a session keeps beside its conversation — a test runner in watch mode, a build, a log being followed. Started by the model or by the person, always listed, always killable. - name: records description: The queryable local record of everything that happened. - name: environments description: >- Where a session's code lives and its commands run — this machine, or a container narya operates. A session that names none runs here. - name: schedules description: >- Work the host's own clock starts with nobody present — a repository, a prompt, a rule and what one fire may spend. Cancel, never destroy. - name: sharing description: >- Publishing a session from a developer's own home to the organisation's, and what is held back before a byte leaves the machine. - name: refinements description: >- What this owner has taught narya and allowed it to keep — distilled facts, and the skills, agents and commands the model wrote for itself. Propose, read, consent, roll back. Nothing here fires until a person answers. - name: platform description: >- Calls Lerian's control plane made to a home it hosts, as this home recorded them. paths: /v1/sessions/{sessionId}/usage: parameters: - $ref: '#/components/parameters/SessionIdParam' get: tags: - sessions summary: Read what one conversation cost, broken down by model description: >- What this conversation has spent, one row per model it was billed under. The session resource already reports the same money as two scalars — `usage.costUsd` over the whole conversation, and `cacheSpend`, which DECOMPOSES part of that same figure rather than adding to it. This is the third view of those same dollars and adds nothing to them either: a conversation that ran on three models reports one number there and says which model spent it here, and the rows sum to that number. The model is the one a round was BILLED under, which is the model that answered and not the one that was asked for. A round this host cannot price contributes its tokens and no dollars, so its group reports costComplete false and its costUsd is a floor. A colleague refused the transcript is refused this. operationId: getSessionUsage parameters: - $ref: '#/components/parameters/CursorParam' - $ref: '#/components/parameters/LimitParam' responses: '200': description: One page of the conversation's consumption. content: application/json: schema: $ref: '#/components/schemas/SessionUsageReport' '400': $ref: '#/components/responses/BadRequest' '403': $ref: '#/components/responses/Forbidden' '404': $ref: '#/components/responses/NotFound' '500': $ref: '#/components/responses/InternalServerError' components: parameters: SessionIdParam: name: sessionId in: path required: true description: The session's id. schema: type: string format: uuid CursorParam: name: cursor in: query required: false description: >- Opaque pagination cursor from a previous page's nextCursor or prevCursor. schema: type: string maxLength: 1024 LimitParam: name: limit in: query required: false description: Maximum items per page. schema: type: integer minimum: 1 maximum: 100 default: 25 schemas: SessionUsageReport: type: object description: >- One conversation's consumption, one page of it, grouped by the model each round was billed under and ordered by model name ascending. required: - sessionId - groupBy - rows properties: sessionId: type: string format: uuid groupBy: type: string description: >- The dimension these rows are grouped by. model is the only one a single conversation has; it is echoed so a client reads the same envelope here as on the period report. enum: - model x-enum-varnames: - SessionUsageReportGroupByModel rows: type: array items: $ref: '#/components/schemas/UsageRow' nextCursor: type: string description: Pass as `cursor` for the next page. Absent on the last page. examples: - sessionId: 6b9f6d2e-1c3a-4f5b-9d7e-2a8c4e6f0b1d groupBy: model rows: - group: claude-opus-4 inputTokens: 120000 outputTokens: 8000 costUsd: 2.4 - group: claude-sonnet-4-5 inputTokens: 2400000 outputTokens: 130000 costUsd: 9.15 UsageRow: type: object description: Consumption for one group over the queried period. required: - group - inputTokens - outputTokens - costUsd properties: group: type: string description: >- The group key: a model id, a UTC day as YYYY-MM-DD, an absolute repository path, a conversation id or a person's opaque subject, depending on groupBy. The literal `private` is the one key that names no repository: it is where the spend of every conversation the caller may not read lands when grouping by repository, so the total still reconciles without publishing a name the caller may not see. Repository paths are absolute, so nothing else can spell it. inputTokens: type: integer minimum: 0 outputTokens: type: integer minimum: 0 cacheReadTokens: type: integer minimum: 0 description: >- Tokens served from the provider's prompt cache over the period. Absent for a period whose rows recorded none. cacheWriteTokens: type: integer minimum: 0 description: >- Tokens written into the provider's prompt cache over the period. Absent for a period whose rows recorded none. costUsd: type: number minimum: 0 costComplete: type: boolean description: >- False when at least one model round in this group recorded no cost at all, which makes costUsd a floor rather than the bill. Pricing is not resolved for every model, so a zero here can mean "free" or "unknown" — this field is what tells them apart, and a reader showing money must say so rather than print a total it cannot stand behind. Absent means the same as true. unpricedRounds: type: integer minimum: 1 description: >- How many model rounds in this group recorded no cost at all — the size of the gap `costComplete: false` reports the existence of. One unpriced round in a thousand and a thousand out of a thousand are both floors, and only this number tells a reader which one they are looking at. Absent when every round in the group was priced, which is when costUsd is the whole of it. examples: - group: claude-sonnet-4-5 inputTokens: 2400000 outputTokens: 130000 costUsd: 9.15 costComplete: true Error: type: object description: >- The single error envelope every operation returns. Codes are NRY- followed by four digits and are catalogued in the top-level x-error-catalog extension. required: - code - title - message properties: code: type: string pattern: ^NRY-[0-9]{4}$ description: Machine-readable error code from the NRY catalogue. title: type: string maxLength: 256 description: Short human-readable summary of the error class. message: type: string maxLength: 4096 description: Specific, actionable description of what went wrong. fields: type: object description: Per-field validation problems. additionalProperties: type: string examples: - code: NRY-0002 title: Session not found message: >- No session with id 6b9f6d2e-1c3a-4f5b-9d7e-2a8c4e6f0b1d exists on this host. responses: BadRequest: description: Malformed request — invalid parameter, cursor, or JSON body. content: application/json: schema: $ref: '#/components/schemas/Error' Forbidden: description: >- The caller is authenticated and is not allowed this operation (NRY-0028 or NRY-0030). content: application/json: schema: $ref: '#/components/schemas/Error' NotFound: description: The addressed resource does not exist on this host. content: application/json: schema: $ref: '#/components/schemas/Error' InternalServerError: description: The host failed — including a store that refuses writes (NRY-0012). content: application/json: schema: $ref: '#/components/schemas/Error' securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: JWT description: >- Enforced on every transport, with no exempt operation. A person's request — over the default local unix socket exactly as over a TCP listener — must carry a JWT issued by the configured identity provider, which the host verifies itself against that issuer's key set: signature, issuer, expiry, and the person and organisation it names. Requests without a valid one receive 401 NRY-0011. The socket's file permissions are transport and are not an authorisation. ````