There used to be a limit of ~100 queries run concurrently for on-demand pricing, such as What is considered a concurrent query in BigQuery?. However, when I go to the quota page now for BQ that line-item is not listed. Is there still a limit on the number of queries that can be run for a project?
When we talk about a concurrency limit, we need to separate that into jobs that can be concurrently given to BigQuery which will eventually run them vs jobs that are allowed to concurrently run.
For concurrent jobs which can be queued for eventual running, you can have 1000 interactive queries and 20,000 batch queries. For concurrently running at the same time, you get to choose using the:
ALTER RESERVATION ... SET OPTIONS(target_job_concurrency=...)
statement. For a complete discussion of this story, please see the docs at Use query queues.