The process took 3 weeks. I interviewed at Slack in Jan 2017
Interview
After a quick phone call with the recruiter, they presented me with a coding exercise. It is a project that you have to finish in one week. My project was a binary memcache protocol implementation (get and set commands only). The protocol is supported by famous memcached. I submitted my implementation on time, and after another week I got a call from the recruiter who informed me that my implementation doesn't meet some never unspecified criteria. I have never been contacted by a Slack engineer. After spending a week, I would expect some technical feedback, discussion, comments, questions. I find that kind of response somewhat unprofessional and disrespectful. If you'd rather not wasting a week, or the exercise isn't something that is very interesting for you, I would not bother with Slack.
Interview questions [1]
Question 1
My project was a binary memcache protocol implementation (get and set/cas commands only). The protocol is supported by famous memcached.
I applied online. The process took 1+ week. I interviewed at Slack (Rancho Cucamonga, CA) in Dec 2016
Interview
Contacted by a recruiter via email. There was a 30 minute phone chat with a recruiter that was not technical ((what's you're favorite thing about slack, tell me about yourself, etc)) After that you are emailed a link to a Codility challenge. The challenge was pretty easy so don't stress to much about it! One question asked you to convert seconds to hr:min:sec format. The others required more thought but yeah, they weren't outrageous. You have 2 hours to complete 3 questions. If you pass this, you go on to speak to a hiring manager. They will ask you more behavioral questions. It's described as a technical discussion. "What don't you like about slack?"
I did not make it past this step but I've heard this is the last step. The process does not seem too hard and I will definitely be trying again in the future.
Interview questions [1]
Question 1
Why slack? What is your favorite slack feature? Tell me about a challenge you have faced
I applied online. The process took 4 weeks. I interviewed at Slack in Nov 2016
Interview
Interview process was surprisingly simple and short for a company of this size. It started with a casual phone interview, then a codility coding challenge, then a video interview with the hiring manager. That's it. They were extremely kind and the questions were very easy. The only problem was communication took forever (like each step involved a 1-2 two week wait for thee next step).