I'm using the latest v0.38.0 version of the k6 with the xk6-output-prometheus-remote extension.
I've tried several scenarios with the constant-arrival-rate executor and always got the same results. The iterations metric was counted two times more than expected.
I've created the simple Counter to prove my theory and got the same 'doubled' results.

Here is an example script:

import http from 'k6/http'; import {Counter} from 'k6/metrics'; export const options = { linger: true, scenarios: { contacts: { executor: 'constant-arrival-rate', duration: '30s', rate: 10, timeUnit: '1s', preAllocatedVUs: 1, maxVUs: 150, }, }, }; const durationCounter = new Counter('dur_counter'); export default function () { var res = http.get('http://test.k6.io'); if (res.status == 200) { durationCounter.add(1); } } 

Here are the results

The number of HTTP requests sent to the server is correct, I've checked on my local machine (10 qps).