Previously fell back to len(tiers[0]) (e.g. 10 for Webshare) when PROXY_CONCURRENCY was unset. Default is now MAX_PROXY_CONCURRENCY=200 so single-URL rotating proxies (DC/residential) run at full concurrency without needing an explicit env var. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>