Wearing a suit to job interviews that you would be doing with 7 years of experience working at a defense contractor is definitely a good idea, assuming you had a favorable experience at the defense contractor and were looking for something similar.
People that did not expect you to wear a suit will be fine with it because they will understand after that long in that formal of a workplace it is reasonable that you expect yourself to wear a suit to interviews and other formal meetings. (If they don't then they would likely be a poor 'culture' fit, once again assuming you liked your previous environment)
People that did expect you to wear a suit, are much less likely to hire if you if you don't.
I dress up a work, even going so far as to put on a tie some days. It has been mentioned by other engineers that they don't feel dressing up is the uniform of an engineer. But I say nuts to that, conformist. I dress up because I don't mind the look, I also like to draw a line between my private wardrobe and my professional one, it helps remind me I still work for "the man" and it drives me forward in the right direction. I say this as a counter point. I buy into the notion of wearing a suit (one that fits).
One time, I wore a suit to an interview (where the recruiter forgot to tell me to wear casual) and was literally mocked for doing so. Not just a good natured ribbing either, this was a good five minutes of really angry tear-down. And this was no startup, they had probably 200+ people. I got to stand there in front of maybe ten interviewers getting "dressed down" for my attire, like some sort of boot camp grunt. I lost all respect for my interviewers at that moment. If a group is so single-minded that me dressing up a little "too much" gets mocking, I'm happy working elsewhere. This same group also picked on me for using Linux instead of a Mac.
If conforming is so important to a group that someone dressing up or using a different OS is so offensive they cannot even pretend to be decent people, I'm happy to see that signal as early as possible.
But please, if you find yourself acting like this: turning down (or even openly mocking) candidates for their formal attire, please consider that you are hiring people who disregarded common wisdom about interviewing. You are hiring people who, when dealing with something as important as interviewing, decided "it's recommended I do x to increase my chances, I'm too cool|awesome|unprofessional to bother with that!"
That doesn't mean mock someone for being sloppy either, I'm just tired of clothes being such a big deal either way.
You'd probably be wrong. Cultural fit may be important, and you don't want to get strange looks on an interview. At the same time the company still might be quite good - as in "early Google"-like good.
I've hold for a while the attitude that if a company pays attention if I'm wearing a suit in a job interview, I shouldn't get a job there.
I don't have anything to complain about that attitude. In retrospect, it saved me from quite a few bad situations that my inexperience would make me accept. But things changed and it does not apply anymore (am not even technically working on IT anymore).
In all seriousness, are suits still a thing for interviews? I don't remember the last time I heard of a company that was anything more than business casual dress (and lets be honest, many firms are much more casual than that).
I'm not in industry, but in CS academia interviews seem to be the one holdout where people do usually wear suits. People attending conferences don't (except in Asia), professors don't, the department chair doesn't, the interview committee themselves probably won't either, but there's a ~70%+ chance that someone interviewing will. Or at least a sport coat and slacks (I guess not technically a suit, but close enough). You probably don't really have to, but people tend to err on that side for an interview in an unknown setting.
at my startup, the dress code is casual/sandals-ok except when meeting with clients.
as a rule, you never want to be under-dressed when meeting with people who you want to give you money. being wrong on this even once could cost you money, possibly a great deal of it.
if you show up in a suit and tie and everyone else is wearing sandals, the proper etiquette is to say "mind if i remove my tie?" and then remove your tie and jacket and unbutton your first shirt button.
instant business casual, which mixes fine with sandals. this also demonstrates social competence which may or may not be a factor in your hiring.
The obvious solution is to enquire about dress code at the company at the time of setting the interview. It doesn't have to be awkward at all - 'what do people wear to the office?' is a perfectly reasonable question. If they say 'business casual', then you can go +1 and wear a suit. If they say 'casual' then turn up in business casual. If they laugh and say 'whatever' then just turn up looking smart and confident.
Thinking that you always have to wear a suit is some type of throwback where the interviewer had all the power - I don't see interviews like that. Interviews should be a mutual meeting of people where they work out if they should work together. An inability to even work out what the dress culture is like before the meeting betrays, to me, an inability to get basic background research in place before any meeting.
So just ask, and then dress appropriately based on the answer given.
yeah, this works, until the boss's boss is also there unannounced, in a suit. meeting of equals? not anymore. it happens in both technical and executive interviews.
the point is not to fit in, the point is to minimize the risk of sartorial faux pas to zero. ZERO.
At many tech companies in SV (not even startups - tech companies like Amazon, Google, etc), it would be a sartorial faux pas to wear a suit to an engineering interview.
you have this impression because your typical engineer will wear a cheap, ill-fitting suit he bought the day before. this will make him look like a schlubby teenager trying to make a good impression among his cooler peers, instead of a manicured professional.
also, the suit isn't going to make you any smarter. you have to be competent. engineers also shy away from suits because they see morons wearing suits. correlation != causation.
show up looking like vint cerf, and the story is different. if you don't know who vint cerf is, look it up. he happens to work for google at this point in time.
I know who Vint Cerf is. One of my friends met Vint Cerf at Google, and I hope you see the irony in citing Vint Cerf. Vint Cerf is viewed within Google as a highly eccentric (aka weird), albeit brilliant, individual. If you come in looking like Vint Cerf for a standard engineering interview, you will look very weird and out of place.
A suit, even a well-tailored, modern cut suit, will be very weird in a software interview at Google.
Don't believe me? Spend a few hours at Google's Mountain View office to get a (admittedly superficial) sense of the culture there.
In my experience, it is very common for the recruiter and/or HR person to suggest what you should wear. If they don't, I would think it somewhat safer not to wear a suit to most tech interviews. (As much as I know y'all want to be all contrarian - "I'm not a nerd, I love looking smart!")
People that did not expect you to wear a suit will be fine with it because they will understand after that long in that formal of a workplace it is reasonable that you expect yourself to wear a suit to interviews and other formal meetings. (If they don't then they would likely be a poor 'culture' fit, once again assuming you liked your previous environment)
People that did expect you to wear a suit, are much less likely to hire if you if you don't.