Career Switch to Senior software engineer /AI engineer?

You're right that breaking into Big Tech (software roles) will lead to a substantial increase in your compensation. With 10 YoE, and 5 as an Application Engineer, you should at least get a mid-level engineer role.

At a FAANG company, you can expect at least $250K total comp (TC). Here's an example job posting at Google.

Let's talk about making the switch in the easiest way:

• I strongly advise against getting a PhD. This is a very long path (4+ years) and you absolutely don't need a doctorate for the vast majority of tech jobs. Unless you have a deep desire to advance the cutting edge of research, the opportunity cost of a PhD is way too large.
• Open source is a great option if you have a specific expertise you want to prove, e.g. a narrative around being a Rust or JavaScript expert. Take a look at the Taro course: Become An Open Source Master.
• The shortest path to getting a software role is to land an interview via a referral. Reconnect with former colleagues who are working in Big Tech now. I'm sure you have coworkers or former students who are now working in target companies. Talk to them to see how they're doing and how their team will evolve over the coming months.

If you find that you're getting interviews from the latter 2 options above, then you should shift aggressively into interview prep mode. You don't need to take any theoretical courses, just shift into DSA/interview prep.

Remember that most "job requirements" are not actually requirements.

I highly recommend against a PhD unless you genuinely love academia. PhDs take so long and PhD students are overworked and underpaid. More thoughts here: "Is having a PhD useful?"

When it comes to any sort of career pivot, I recommend switching internally. It's way better and feasible as the company takes on less risk. So the idea is that you're a mid-level or senior back-end/full-stack SWE at a company, prove yourself, and then ask for an internal transfer to MLE. This path is the most feasible at Big Tech companies with high internal mobility. Meta and Google are famous for their top-notch team switching culture in particular.

There's an amazing AMA happening right now about ML/AI career paths too. Check it out if you haven't already: "Looking to transition to ML Engineer? What do you want to know?"