Class OpenAIApi

packages/openai-adapters/src/apis/OpenAI.ts:35–292

} from "./openaiResponses.js";

export class OpenAIApi implements BaseLlmApi {
  openai: OpenAI;
  apiBase: string = "https://api.openai.com/v1/";

  constructor(protected config: z.infer<typeof OpenAIConfigSchema>) {
    this.apiBase = config.apiBase ?? this.apiBase;

    // Always create the original OpenAI client for fallback
    this.openai = new OpenAI({
      // Necessary because `new OpenAI()` will throw an error if there is no API Key
      apiKey: config.apiKey ?? "",
      baseURL: this.apiBase,
      fetch: customFetch(config.requestOptions),
      timeout: config?.requestOptions?.timeout || undefined,
    });
  }
  modifyChatBody<T extends ChatCompletionCreateParams>(body: T): T {
    // Add stream_options to include usage in streaming responses
    if (body.stream) {
      (body as any).stream_options = { include_usage: true };
    }

    // DeepSeek reasoner models use max_completion_tokens instead of max_tokens
    if (
      body.max_tokens &&
      (this.apiBase?.includes("api.deepseek.com") ||
        body.model.includes("deepseek-reasoner"))
    ) {
      body.max_completion_tokens = body.max_tokens;
      body.max_tokens = undefined;
    }

    // o-series models - only apply for official OpenAI API
    const isOfficialOpenAIAPI = this.apiBase === "https://api.openai.com/v1/";
    if (isOfficialOpenAIAPI) {
      if (body.model.startsWith("o") || body.model.includes("gpt-5")) {
        // a) use max_completion_tokens instead of max_tokens
        body.max_completion_tokens = body.max_tokens;
        body.max_tokens = undefined;

        // b) use "developer" message role rather than "system"
        body.messages = body.messages.map((message) => {
          if (message.role === "system") {
            return { ...message, role: "developer" } as any;
          }
          return message;
        });
      }
      if (body.tools?.length && !body.model.startsWith("o3")) {
        body.parallel_tool_calls = false;
      }
    }
    return body;
  }

  protected shouldUseResponsesEndpoint(model: string): boolean {
    if (this.config.useResponsesApi === false) {
      return false;