> ## Documentation Index > Fetch the complete documentation index at: https://docs.ninjachat.ai/llms.txt > Use this file to discover all available pages before exploring further. # Create a chat completion (legacy path) > Supported compatibility surface — kept working indefinitely, but not the path for new integrations. Modern equivalent: `POST /responses`. Backward-compatible path for /chat/completions, including historical field spellings and session memory. ## OpenAPI ````yaml /openapi.json post /chat openapi: 3.1.0 info: title: NinjaChat API version: 1.0.0 description: >- Clean-break NinjaChat v1. Chat and Responses bill actual token usage; images and videos use catalog unit pricing. servers: - url: https://www.ninjachat.ai/api/v1 security: [] paths: /chat: post: summary: Create a chat completion (legacy path) description: >- Supported compatibility surface — kept working indefinitely, but not the path for new integrations. Modern equivalent: `POST /responses`. Backward-compatible path for /chat/completions, including historical field spellings and session memory. parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: content: application/json: schema: type: object properties: {} responses: '200': description: Chat completion or SSE stream. content: application/json: schema: $ref: '#/components/schemas/ChatCompletionResponse' text/event-stream: schema: type: string '400': description: Invalid or unsupported request parameter. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '401': description: Missing or invalid API key. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '402': description: Insufficient balance or project spend limit reached. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '429': description: Rate limit exceeded. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '500': description: Gateway error. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - bearerAuth: [] components: parameters: IdempotencyKey: name: Idempotency-Key in: header required: false schema: type: string minLength: 1 maxLength: 255 description: >- Safely retry the same logical write without duplicate billing or execution. schemas: ChatCompletionResponse: type: object properties: cost: type: object properties: this_request: type: string per_image: type: string per_video: type: string images: type: integer minimum: 0 required: - this_request additionalProperties: false balance: type: string metadata: type: object properties: latency_ms: type: number minimum: 0 group: type: string search_depth: type: string results_count: type: integer minimum: 0 required: - latency_ms additionalProperties: false id: type: string object: type: string enum: - chat.completion created: type: integer model: type: string minLength: 1 maxLength: 160 resolved_model: type: string minLength: 1 maxLength: 160 provider: type: - string - 'null' choices: type: array items: type: object properties: index: type: integer message: type: object properties: role: type: string enum: - assistant content: type: - string - 'null' reasoning_content: type: string tool_calls: type: array items: type: object properties: id: type: string minLength: 1 maxLength: 128 type: type: string enum: - function extra_content: type: object properties: google: type: object properties: thought_signature: type: string minLength: 1 required: - thought_signature additionalProperties: false additionalProperties: false function: type: object properties: name: type: string minLength: 1 maxLength: 64 arguments: type: string required: - name - arguments additionalProperties: false required: - id - type - function additionalProperties: false required: - role - content additionalProperties: false finish_reason: type: - string - 'null' required: - index - message - finish_reason additionalProperties: false usage: $ref: '#/components/schemas/ChatUsage' cost_usd: type: number minimum: 0 request_id: type: string routing: $ref: '#/components/schemas/RoutingSummary' required: - id - object - created - model - resolved_model - provider - choices - usage - cost_usd - request_id - routing additionalProperties: false ErrorResponse: type: object properties: error: type: object properties: message: type: string type: type: string code: type: string param: type: - string - 'null' required: - message - type - code additionalProperties: false required: - error additionalProperties: false ChatUsage: type: object properties: prompt_tokens: type: integer minimum: 0 completion_tokens: type: integer minimum: 0 total_tokens: type: integer minimum: 0 prompt_tokens_details: type: object properties: cached_tokens: type: integer minimum: 0 cache_creation_tokens: type: integer minimum: 0 additionalProperties: false completion_tokens_details: type: object properties: reasoning_tokens: type: integer minimum: 0 additionalProperties: false required: - prompt_tokens - completion_tokens - total_tokens additionalProperties: false RoutingSummary: type: object properties: strategy: type: string enum: - balanced - cost - latency - quality requested_models: type: array items: type: string minLength: 1 maxLength: 160 resolved_model: type: string minLength: 1 maxLength: 160 provider: type: - string - 'null' provider_attempts: type: array items: $ref: '#/components/schemas/ProviderAttemptReceipt' fallbacks_allowed: type: boolean data_policy: type: string enum: - default - no_training - zero_retention caching: type: string enum: - auto source: type: string enum: - request - project - default router: $ref: '#/components/schemas/RouterDecisionSummary' required: - strategy - requested_models - resolved_model - provider - fallbacks_allowed - data_policy additionalProperties: false ProviderAttemptReceipt: type: object properties: provider: type: string outcome: type: string enum: - served - failed_over - failed attempt_index: type: integer minimum: 0 required: - provider - outcome - attempt_index additionalProperties: false RouterDecisionSummary: type: object properties: id: type: string enum: - ninja/auto task: type: string classified_by: type: string enum: - regex - llm - llm-cached override: type: - string - 'null' enum: - long_context - multilingual reasoning: type: string candidates: type: array items: type: string minLength: 1 maxLength: 160 considered: type: array items: type: object properties: {} required: - id - task - classified_by - override - reasoning - candidates - considered additionalProperties: false securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: NinjaChat API key description: Use an API key created in the NinjaChat developer console. ````