Turkish Airlines carry-on baggage restrictions--how strict are they?

They absolutely will not care .... except on the day that they do. If they do, why risk it. I suggest you watch Midnight Express (1978).

I suspect I flew them Houston to Istanbul to Budapest and back 30 times over the years. Often enough I knew 2 flight attendants. TA has some of the best staff I have experienced on an airline. They treated me with respect and I returned it by following the rules. I csn think of a few times when I had my carryon measured. Personal item too.

As Mr. E wisely said, there's no way to know if they will enforce the rules until they do. Best to meet their guidelines as best you can. I don't know about Turkish Airlines, but on my recent Delta flight as we were boarding, they announced which zones would probably have to gate check their bags due to space. I also don't like checking a bag but did so on a recent trip - it survived and so did I. Just don't put anything you need immediately in it (e.g. medications, contact lenses, etc.)

I also want to give myself the option of bringing an extra carry on
as I'd like to pick up souvenirs and will be away from home for a
total of one month (though not all that time will be spent in Turkey).

Try searching the forum for "packable bags" and you'll get a host of suggestions for something you can stash in your carry on that you can use coming home. https://search.ricksteves.com/?button=&date_range=1y&filter=Travel+Forum&query=packable+bag

Are you feeling lucky? [/clint eastwoood]

I fly Turkish Airlines regularly, I'm actually a big fan, and my experiences with how strict/not-strict they are about enforcing their carry-on bag limits is: it's completely random. They are actually VERY strict sometimes, and other times they do not pay any attention at all to it. Once, checking in for a long-haul international business class ticket, they weighed and measured our carry-ons, and told us our carry-ons were too heavy (we were forced to split up the contents of our carry-on into two carry-ons, which together weighed the same, but they said that was OK...go figure). From a logical standpoint this was insane - presumably they weigh bags to ensure the aircraft weight and balance is managed, but we ended up carrying on the exact same stuff, just separated into two containers). Note that typically in business class, most airlines are a lot looser about cabin baggage rules. Not that airline on that day, for us.

On another TK flight, everyone had big, heavy rolling suitcases as carry-ons (they all looked about 10X as heavy as the stated weight limit) but nobody batted an eye.

So based on my experience, I don't think one can predict how loose or strict they will be. My suggestion is to prepare accordingly, and don't expect eveything to make sense.

Thank you Mr. E, CL and David. Based on your comments, I'm going to check my roller suitcase and just carry on my backpack and small purse and hope for the best!