Thorough, challenging but never unprofessional or rude or negative.
First stage: Introductory screening call with internal recruiter.
Second stage: A homework assignment lasting up to a week. It could be a coding assignment or maybe draw up a network design or it could be design a new datacenter deployment. It just depends on the role you're interviewing for. Questions and conversations are encouraged.
Third stage: A review interview on your homework assignment. An hour where you're invited to present your work, explore what you did and how you did it. You'll be subtly challenged but in a way which unpicks your thought process and knowledge.
Fourth Stage: a troubleshooting session for an hour and a half. You'll be set various challenges and then invited to work through them with one or two interviewers. Can turn into an excellent round table discussion and a really enlightening session.
Fifth Stage: An interview with a senior manager covering cultural aspects, values, etc
An offer came the following week. In all the process is challenging and exhaustive but always done in an atmosphere of respect and curiosity. I'd encourage Wave not to change this approach!