I’ve heard that the jump from Sr. PM to the “next level” (e.g Principal or Group PM) often comes with a steep learning curve. Is that true, and how would one prepare to solidify the right foundation to ease the transition preemptively?

The biggest struggle I have observed is related to transition from an individual level product craft growth to growing that of a group. Andy Grove in High Output Management said "Managers are responsible for increasing the output of their organizations and neighboring organizations they influence". Read this sentence again and again. The learning curve is in learning how to optimize for the outputs of your team vs. your own. This means that you need to make trade-offs across your teammates and their areas, as well as help each of them grow as much as possible. 

My recommendation is to read up on team management in all contexts - business, military, sports have great writings on it; there are also many articles and videos from leaders of all kinds. Then, ask yourself (before you were to manage a team), how would I change my prioritization frameworks, rituals, interactions, communication style if I were to optimize for an output of a team of PMs. You can even hypothsize about it using your existing team - if you are a manager tomorrow, what would you do differently to optimize for the greatest output? 

Simply thinking and writing your thoughts down on this topic, as well as honing in on skills I mentioned above in the "director level" answer should help you prepare for the transition. 

It can definitely be a steep learning curve, because at Staff+ PM level you are expected to have strengths in one or more areas of product management that aren't often exercised at lower levels. Some examples:

• Having a much wider aperture and being able to develop and sell portfolio-level (not just product or feature-level) product strategy that can touch other areas of the company
• Assessing and making build vs. borrow vs. buy recommendations & understanding how to work with a channel/partner/business development team
• Coaching and mentoring other PMs and reviewing their work
• Portfolio-level goal setting and roadmap management
• Organizational design (how to do it, when to change it, influencing your engineering & design peers to restructure their org structure as the product evolves)
• Preparation of executive-level communications (how to convey only the most important information in the most concise manner possible)

The good thing is that you are not expected to be excellent in each of these areas right out of the gate. But it helps to do a couple of things if you are aiming for Staff+ IC in your career:

• Pick one of these areas and figure out how you can proactively pick up opportunities to learn and improve now. If you plan to stay at your current company, it helps to pick something that is a gap/weakness in the organization to make yourself more valuable.
• Focus your reading / learning / professional development / networking in the PM community towards that topic, so you gain some outside perspective on it.
• Be transparent with your manager about your career aspirations and what you are doing to level up in at least one of these competencies -- and hopefully align that growth with something that your manager needs in the group.

I will mention one exception to all of the above. It is possible at some companies to become Staff+ PM simply by having more historical and domain knowledge than anyone else such that you become the "product oracle" for that area. In these situations, a breadth of skills outside of that domain knowledge is less necessary. Just remember that there can only be one oracle; once you choose that path, it is hard to get a Staff+ PM job elsewhere unless that company specifically needs the same wealth of knowledge.

In my experience, the learning curve happens in the current role, as a prerequisite to transitioning into the next. You have to be operating at the next level already and there really isn't an easing of the transition beyond that. For example, managing wider scope, solving harder problems, navigating trickier interpersonal dynamics, connecting more "dots", communicating with more clarity on more complex matters, and influencing more people and outcomes, are among some of the skills needed at every PM level, but to different degrees. As you showcase these skills you are already solidifying the foundation for the next level. One of the biggest learning challenges can however come at later levels - when transitioning from IC to manager (irrespective of the accompanying title), partially because it is a binary situation. You are either a manager of people or you are not; there is not much preparing or gradual transition.

Relatedly, many PMs are seeking that check-list, that when done, spells promotion. Consequently, one of the most frustrating and non-actionable things that managers can say is "you are not ready yet", perpetuating a bit of the feeling that there is some transition or steep learning that one must overcome. Often it means the manager is not ready to do that for you but is uncomfortable giving you specifics. Or it is not possible in the current org strucure. Sometimes, they just don't know themselves, but they'll know it when they see it. Perhaps, that is a big hint. Observe how others at the next level are operating as preparation. How big are their projects? How much more do you have to know or do? The criteria can be very different by company, that's why it's important to know any published leveling criteria. But generally, even then, there aren't a lot of clear-cut check boxes. Sometime the criteria are only in your managers head. I once had a manager tell me that if I grew my product to $50M or $100M in revenue it would get me promoted. (My answer was to remind them that we were working on 5-year incubation, hence low likelihood of multimillion dollar outcomes on any reasonable timelines, and that this criteria should have been articulated a lot earlier in the job decription. Plus there were plenty of examples of promotions without that criteria - so the aforementioned criteria disappeared from our conversations.) 

In all cases, cross-reference everything official with what you actually see happens day-to-day and what behaviors or results are rewarded at the next level. Perhaps, the steepest learning curve is learning what specifically gets you promoted at your particular company and with your particular management chain.

Love the proactive thinking and the desire to excel :)

Not sure if the learning curve is any steeper but there are a few things that can support career growth:

• Master the craft for what is required of you in the current seniority.
• Get exposure to delegating more work, creating leverage across different teams, and see if you are able to 'let go of the detailed tasks' but still bring a beautiful product to life with your team.
• Get exposure to market maps, strategy documents, start asking thoughtful questions in various forums with leadership - not to be the loudest voice but more to build the sharpest brain.
• Invest and re-invest in building relationships with cross-functional partners across the company. Learn how they think about their work.
• Try unblocking others - what does it take to pinpoint what is holding back someone and how can you help them be successful? What is your personal style as you do that?