Sadly you’re right, the new runtimes no longer attach app-level log messages to HTTP request logs like they did in the old Python 2 runtime. Details in GitHub issue googleapis/python-logging#110. The app level logs generally go to projects/[APP_ID]/logs/stdout, while the HTTP request logs are in projects/[APP_ID]/logs/appengine.googleapis.com%2Frequest_log.

(It’s a bit more complicated, eg the google-cloud-logging library does try to attach the logs, at least for a couple modern web frameworks, but it doesn’t try too hard.)

To do it yourself, you pull out the X-Cloud-Trace-Context HTTP request header and add it to the log record’s trace attribute, in the format projects/[APP_ID]/traces/[TRACE_ID]. Example code here.

Detailed logs no longer show in logs explorer from AppEngine