Indeed processing the stream fully and queuing up the function calls does the job, thank you! The code below does the job: let functionCalls: ResponseFunctionToolCall[] = []; do { // Process text messages. ({ assistantMessage, functionCalls } = await this.streamResponse(input, { assistantMessage, conversation, toolChoice: this.getToolChoice(someData), tools, user, })); // Process function calls. input = []; for (const functionCall of functionCalls) { const res = await this.processFunctionCall(tarotReading, functionCall); someData = res.someData; input = [...input, ...res.input]; } } while (functionCalls.length);