> ## Documentation Index > Fetch the complete documentation index at: https://docs.arcuserp.com/llms.txt > Use this file to discover all available pages before exploring further. # Retrieve a lot > Returns a single lot with an `inventory_summary` aggregate of its quantity on hand, included only on this call and not on the list. Supports ETag caching via `If-None-Match`; requires `lots:read` scope. ## OpenAPI ````yaml /openapi.yaml get /lots/{id} openapi: 3.1.0 info: title: Arcus ERP Public API version: 1.0.0 description: > Arcus ERP public REST API. Designed for external integrations and data migration. **Authentication.** Bearer token (API key) via the `Authorization` header. Format: `Authorization: Bearer ark_live_ent__` (or `ark_test_*` for sandbox). API keys are issued per-entity in **Settings > Developers > API Keys**. **Entity scoping.** The entity is encoded in the API key prefix; routes are flat (e.g. `/v1/accounts`, `/v1/orders`, `/v1/products`). A small set of platform endpoints (migration, reconciliation, events, webhook endpoints, API keys) use the `/v1/entities/{entity_id}/...` form -- those are noted in their tags. **Key capabilities.** - Related-resource hydration via `?expand[]=` (see `x-arcus-expand` on each resource). - Cursor-based pagination (`starting_after` / `ending_before` / `limit`). - Idempotency via the `Idempotency-Key` header. - Webhook events for asynchronous notification. - Conditional requests / ETag for cache validation. **Changelog.** Entries are dated and name every published contract whose MEANING moved, not only the ones whose field names changed. The narrative version of the same entries, written for integrators, is published at https://arcuserp.mintlify.app/changelog. **2026-09-22 (planned 2026-09-21), REORDER-BUYER-TRUTH: demand changed what it MEANS on three published contracts, with no field renamed.** An integrator that pins field names sees no breakage and different numbers, which is why this entry exists. - **Demand now counts build consumption.** `demand_avg_per_day` on the public product, kit and inventory-balance objects, and `daily_demand` / `demand_basis` / `net_suggested_qty` on `GET /v1/purchasing/reorder-report`, are composed from fulfilled sales lines PLUS posted `build_consume` inventory draws: each physical decrement of a product counts exactly once. The previous rule adopted an internal-consumption basis only when the sales blend was exactly zero, so a product both sold AND consumed into work orders planned as if the build draws did not exist. Products drawn into work orders move; on one production-shaped dataset five did, the largest from 0.05/day to 14.95/day. - **`demand_basis` now carries four values, not two:** `sales`, `sales_and_builds`, `builds` and `consumption`. A consumer with a two-branch reader (anything that is not `consumption` is `sales`) silently hides the two new ones. - **`current_demand_units` on `GET /v1/inventory/balances/:id` moved, by a second rule.** It counts committed-but-unshipped CUSTOMER demand, and it now counts a kit component's own line rather than its parent kit line, and excludes non-sales documents. On one production dataset 269 of 1,043 balance rows changed, 227 of them downward; the largest single move was 1,941 to 25, on a product whose open PURCHASE order line had been reported as customer demand. Re-baseline anything that alerts or reorders off this field. - `run_rate_30/90/180/365` and `blended_daily` on the same balance object move for the first reason above. - **Added, not changed:** `GET /v1/purchasing/reorder-report` accepts `demand_window` and returns the unit, cover-through and reorder-point-provenance fields documented on that operation; `order_multiple` is accepted and returned on the product-vendor doors. - **Volume note.** The `inventory.low_stock`, `inventory.out_of_stock` and `inventory.back_in_stock` webhook events are population-gated on `on_hand <= reorder_point`, and reorder points move with the demand above, so subscribers should expect a one-time step change in event volume around the release. servers: - url: https://api.arcuserp.com/v1 description: Arcus ERP API (accepts both live `ark_live_*` and test `ark_test_*` keys) - url: https://dev-api.arcuserp.com/v1 description: >- Dev sandbox API (test-only data, accepts `ark_test_*` keys against dev RDS) security: [] paths: /lots/{id}: parameters: - name: id in: path required: true schema: type: string format: uuid get: tags: - Lots summary: Retrieve a lot description: >- Returns a single lot with an `inventory_summary` aggregate of its quantity on hand, included only on this call and not on the list. Supports ETag caching via `If-None-Match`; requires `lots:read` scope. operationId: getLotV1 parameters: - name: If-None-Match in: header required: false schema: type: string responses: '200': description: Lot with inventory summary content: application/json: schema: $ref: '#/components/schemas/Lot' headers: ETag: schema: type: string '304': description: Not modified (ETag matched) '404': $ref: '#/components/responses/Error' security: - ApiKeyAuth: - lots:read components: schemas: Lot: type: object description: > A lot-tracked production batch of a product. Created when receiving lot- tracked inventory and consumed via FEFO (first-expiry-first-out) at allocation time. Status walks `active -> on_hold -> expired -> recalled` via the change-status endpoint. Soft-delete refuses when `quantity_on_hand > 0` (HTTP 409). Scope: lots:read / lots:write / lots:delete. Rule 23 SSOT: `quantity_on_hand` is written only by canonical inventory_transactions postings; the API never writes it directly. properties: id: type: string format: uuid readOnly: true object: type: string example: lot entity_id: type: string format: uuid readOnly: true product_id: type: string format: uuid lot_code: type: string description: Operator-supplied or vendor-supplied lot identifier. 1..100 chars. vendor_id: type: string format: uuid nullable: true manufacture_date: type: string format: date nullable: true expiration_date: type: string format: date nullable: true received_at: type: string format: date-time nullable: true cost: type: number format: float nullable: true description: Per-unit landed cost at receipt (USD). quantity_received: type: number format: float description: Original receive quantity. Immutable after creation. quantity_on_hand: type: number format: float readOnly: true description: 'Current on-hand. SSOT: derived via inventory_transactions.' quantity_consumed: type: number format: float readOnly: true quantity_written_off: type: number format: float readOnly: true status: type: string enum: - active - on_hold - expired - recalled description: >- Lifecycle state. Changed via POST /lots/{id}/change-status with mandatory reason. example: active notes: type: string nullable: true external_source: type: string nullable: true description: Migration provenance (e.g. versa, bubble). external_id: type: string nullable: true metadata: type: object description: Free-form caller metadata. Default {}. inventory_summary: type: object readOnly: true description: >- Computed aggregate joined on lot_id from inventory.inventory_transactions. Only on GET /lots/{id}, not on list. properties: on_hand: type: number format: float description: >- Sum of inventory_transactions.quantity for this lot, scoped to entity. created_at: type: string format: date-time readOnly: true updated_at: type: string format: date-time readOnly: true ErrorEnvelope: type: object description: | Canonical error response envelope. All API errors use this shape. required: - error - code properties: error: type: string description: Machine-readable error key example: not_found code: type: string description: Machine-readable error code (often same as error) example: not_found type: type: string enum: - validation_error - permission_error - not_found - conflict - rate_limit - internal - expand_error - not_implemented example: not_found hint: type: string description: Human-readable one-sentence explanation (English) example: >- The requested order does not exist or does not belong to this entity. param: type: string description: The parameter that caused the error, if applicable example: expand[0] required: type: string description: The scope required (only on insufficient_scope errors) example: accounts:read request_id: type: string description: >- Unique request ID for support tracing (maps to CloudWatch log stream) example: req_abc123 responses: Error: description: Error response (400/401/403/404/409/422/429/500) content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' securitySchemes: ApiKeyAuth: type: http scheme: bearer description: | API key issued per entity via Settings > Developers > API Keys. Each key carries scopes (e.g. orders:read, products:write). Bearer token format: Authorization: Bearer ark_live_ent__ Test keys use ark_test_ent__. Both are issued per entity via Settings > Developers > API Keys. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.