Thinking about insights that were particularly relevant for me / my values:

• Reducing long-term risks from malevolent actors as a potentially promising cause area
• The importance of developing (the precursors for) peaceful bargaining strategies
• Related: Anti-realism about bargaining? (I don't know if people still believed this in 2015, but early discussions on Lesswrong seemed to indicate that a prevalent belief was that there exists a proper solution to good bargaining that works best independently of the decision architecture of other agents in the environment.)
• Possible implications of correlated decision-making in large worlds
• Arguably, some people were thinking along these lines before 2015. However, so many things fall under the heading of "acausal trade" that it's hard to tell, and judging by conversations with people who think they understood the idea but actually mixed it up with something else, I assign 40% to this having been relevantly novel.
• Some insights on metaethics might qualify. For instance, the claim "Being morally uncertain and confidently a moral realist are in tension" is arguably a macrostrategically relevant insight. It suggests that more discussion of the relevance of having underdetermined moral values (Stuart Armstrong wrote about this a lot) seems warranted, and that, depending on the conclusions from how to think about underdetermined values, peer disagreement might work somewhat differently for moral questions than for empirical ones. (It's hard to categorise whether these are novel insights or not. I think it's likely that there were people who would have confidently agreed with these points in 2015 for the right reasons, but maybe lacked awareness that not everyone will agree on addressing the underdetermination issue in the same way, and so "missed" a part of the insight.)

I think there haven’t been any novel major insights since 2015, for your threshold of “novel” and “major”.

Notwithstanding that, I believe that we’ve made significant progress and that work on macrostrategy was and continues to be valuable. Most of that value is in many smaller insights, or in the refinement and diffusion of ideas that aren’t strictly speaking novel. For instance:

• The recent work on patient longtermism seems highly relevant and plausibly meets the bar for being “major”. This isn’t novel - Robin Hanson wrote about it in 2011, and Benjamin Franklin arguably implemented the idea in 1790 - but I still think that it’s a significant contribution. (There is a big difference between an idea being mentioned somewhere, possibly in very “hidden” places, and that idea being sufficiently widespread in the community to have a real impact.)
• Effective altruists are now considering a much wider variety of causes than in 2015 (see e.g. here). Perhaps none of those meet your bar for being “major”, but I think that the “discovery” (scare quotes because probably none of those is the first mention) of causes such as Reducing long-term risks from malevolent actors, invertebrate welfare, or space governance constitutes significant progress. S-risks have also gained more traction, although again the basic idea is from before 2015.
• Views on the future of artificial intelligence have become much more nuanced and diverse, compared to the relatively narrow focus on the “Bostrom-Yudkowsky view” that was more prevalent in 2015. I think this does meet the bar for “major”, although it is arguably not a single insight: relevant factors include takeoff speeds, whether AI is best thought of as a unified agent, or the likelihood of successful alignment by default. (And many critiques of the Bostrom-Yudkowsky view were written pre-2015, so it also isn't really novel.)

Maybe: "We should give outsized attention to risks that manifest unexpectedly early, since we're the only people who can."

(I think this is borderline major? The earliest occurrence I know of was 2015 but it's sufficiently simple that I wouldn't be surprised if it was discovered multiple times and some of them were earlier.)

Elsewhere on the forum, I asked Ajeya Cotra of Open Phil some questions inspired by this post. What follows are my questions [in square brackets] and her answers.

[1. Do you think many major insights from longtermist macrostrategy or global priorities research have been found since 2015?]

I think "major insights" is potentially a somewhat loaded framing; it seems to imply that only highly conceptual considerations that change our minds about previously-accepted big picture claims count as significant progress. I think very early on, EA produced a number of somewhat arguments and considerations which felt like "major insights" in that they caused major swings in the consensus of what cause areas to prioritize at a very high level; I think that probably reflected that the question was relatively new and there was low-hanging fruit. I think we shouldn't expect future progress to take the form of "major insights" that wildly swing views about a basic, high-level question as much (although I still think that's possible).

[2. If so, what would you say are some of the main ones?]

Since 2015, I think we've seen good analysis and discussion of AI timelines and takeoff speeds, discussion of specific AI risks that go beyond the classic scenario presented in Superintellilgence,  better characterization of multipolar and distributed AI scenarios, some interesting and more quantitative debates on giving now vs giving later and "hinge of history" vs "patient" long-termism, etc. None of these have provided definitive / authoritative answers, but they all feel useful to me as someone trying to prioritize where Open Phil dollars should go.

[3. Do you think the progress has been at a good pace (however you want to interpret that)?]

I'm not sure how to answer this; I think taking into account the expected low-hanging fruit effect, and the relatively low investment in this research, progress has probably been pretty good, but I'm very uncertain about the degree of progress I "should have expected" on priors.

[4. Do you think that this pushes for or against allocating more resources (labour, money, etc.) towards that type of work?]

I think ideally the world as a whole would be investing much more in this type of work than it is now. A lot of the bottleneck to this is that the work is not very well-scoped or broken into tractable sub-problems, which makes it hard for a large number of people to be quickly on-boarded to it.

[5. Do you think that this suggests we should change how we do this work, or emphasise some types of it more?]

Related to the above, I'd love for the work to become better-scoped over time -- this is one thing we prioritize highly at Open Phil.

(See also my response to Ajeya.)

My quick take:

• I agree with other answers that in terms of "discrete" insights, there probably wasn't anything that qualifies as "major" and "novel" according to the above definitions.
• I'd say the following were the three major broader developments, though unclear to what extent they were caused by macrostrategy research narrowly construed:
  • Patient philanthropy: significant development of the theoretical foundations and some practical steps (e.g. the Founders Pledge research report on potentially setting up a long-term fund).
    • Though the idea and some of the basic arguments probably aren't novel, see this comment thread below.
  • Reduced emphasis on a very small list of "top cause areas". (Visible e.g. here and here, though of course there must have been significant research and discussion prior to such conclusions.)
  • Diversification of AI risk concerns: less focus on "superintelligent AI kills everyone after rapid takeoff because of poorly specified values" and more research into other sources of AI risk.
    • I used to think there was less actual as opposed to publicly visible change, and less due to new research to the extent there was change. But it seems that a perception of significant change is more common.

In previous personal discussions, I think people have made fair points around my bar maybe being generally unreasonable. I.e. it's the default for any research field that major insights don't appear out of nowhere, and that it's almost always possible to find similar previous ideas: in other words, research progress being the cumulative effect of many small new ideas and refinements of them.

I think this is largely correct, but that it's still correct to update negatively on the value of research if past progress has been less good on the spectra of majority and novelty. However, overall I'm now most interested in the sort of question asked here to better understand what kind of progress we're aiming for rather than for assessing the total value of a field.

FWIW, here are some suggestions for potential "major and novel" insights others have made in personal communication (not necessarily with a strong claim made by the source that they meet the bar, also in some discussions I might have phrased my questions a bit differently):

• Nanotech / atomically precise manufacturing / grey goo isn't a major x-risk
  • [NB I'm not sure that I agree with APM not being a major x-risk, though 'grey goo' specifically may be a distraction. I do have the vague sense that some people in, say, the 90s or until the early 2010s were more concerned about APM then the typical longtermist is now.]
  • My comments were: 
    • "Hmm, maybe though not sure. Particularly uncertain whether this was because new /insights/ were found or just due to broadly social effects and things like AI becoming more prominent?"
    • "Also, to what extent did people ever believe this? Maybe this one FHI survey where nanotech was quite high up the x-risk list was just a fluke due to a weird sample?"
  • Brian Tomasik pointed out: "I think the nanotech-risk orgs from the 2000s were mainly focused on non-grey goo stuff: http://www.crnano.org/dangers.htm"
• Climate change is an x-risk factor
  • My comment was: "Agree it's important, but is it sufficiently non-obvious and new? My prediction (60%) is that if I asked Brian [Tomasik] when he first realized that this claim is true (even if perhaps not using that terminology) he'd point to a year before 2014."
• We should build an AI policy field
  • My comment was: "[snarky] This is just extremely obvious unless you have unreasonably high credence in certain rapid-takeoff views, or are otherwise blinded by obviously insane strawman rationalist memes ('politics is the mind-killer' [aware that this referred to a quite different dynamic originally], policy work can't be heavy-tailed [cf. the recent Ben Pace vs. Richard Ngo thing]). [/snarky]
  • I agree that this was an important development within the distribution of EA opinions, and has affected EA resource allocation quite dramatically. But it doesn't seem like an insight that was found by research narrowly construed, more like a strategic insight of the kind business CEOs will sometimes have, and like a reasonably obvious meme that has successfully propagated through the community."
• Surrogate goals research is important
  • My comment was: "Okay, maaybe. But again 70% that if I asked Eliezer when he first realized that surrogate goals are a thing, he'd give a year prior to 2014."
• Acausal trade, acausal threats, MSR, probable environment hacking
  • My comment was: "Aren't the basic ideas here much older than 5 years, and specifically have appeared in older writings by Paul Almond and have been part of 'LessWrong folklore' for a while?Possible that there's a more recent crisp insight around probable environment hacking -- don't really know what that is."
• Importance of the offense-defense balance and security
  • My comment was: "Interesting candidate, thanks! Haven't sufficiently looked at this stuff to have a sense of whether it's really major/important. I am reasonably confident it's new."
    • [Actually I'm not a bit puzzled why I wrote the last thing. Seems new at most in terms of "popular/widely known within EA"?]
• Internal optimizers
  • My comment was: "Also an interesting candidate. My impression is to put it more in the 'refinement' box, but that might be seriously wrong because I think I get very little about this stuff except probably a strawman of the basic concern."
• Bargaining/coordination failures being important
  • My comment was: "This seems much older [...]? Or are you pointing to things that are very different from e.g. the Racing to the Precipice paper?"
• Two-step approaches to AI alignment
  • My comment was: "This seems kind of plausible, thanks! It's also in some ways related to the thing that seems most like a counterexample to me so far, which is the idea of a 'Long Reflection'. (Where my main reservation is whether this actually makes sense / is desirable [...].)"
• More 'elite focus'
  • My comment was: "Seems more like a business-CEO kind of insight, but maybe there's macrostrategy research it is based on which I'm not aware of?"

Patient philanthropy?

Completely out of my depth here, but I wondered if Robin Hanson's "Age of Em" would be considered as a new insight for longtermists along the lines of making the case that brain emulations could also "be a technology with impacts comparable to the Industrial Revolution, and [whose] impacts may not be close-to-optimal by default"

This may sound really obvious in retrospect, but Evan G. Williams' 2015 paper (summarized here) felt pretty convincing to me that conditional upon moral realism being broadly true, we're all almost certainly unknowingly guilty of large moral atrocities. 

There's several steps here that I think is interesting:

1. We may believe that this is a problem only for the "rest" of society; as enlightened vegan cosmopolitan longtermists, we see all the moral flaws that others do not.
   1. But this just has both a really bad historical track record and isn't very logically convincing, see below
2. The inductive argument: No society that thinks of itself as just historically has been devoid of what we now consider grave moral wrongs.
   1. Further, we're in a time of upheaval. A society that has everything right likely is only a generation removed from a society that has almost everything right.
3. The disjunctive argument: There are so many different ways that we could be morally wrong that we may/may not be aware of, and many of them are in tension with each other.
4. Hedging (e.g. don't eat insects on the off chance insects have moral value)does not robustly work as a strategy to mitigate unknown ongoing moral catastrophe.
   1. Because of the disjunction above, and the sheer number of ways we could be wrong.

Even though I'm not a moral realist, I feel like this paper had a substantial effect on how I view the demands of morality, and over the years I've slowly internalized the message that this type of thing is hard (I'm also maybe 15% less optimistic about moral hedging as a robust strategy than I otherwise would've been if I hadn't read this paper). 

These points feel so obvious in retrospect that I'd be surprised if they weren't all covered before 2015, so I'd be interested in whether philosophers and philosophy students here can point to earlier sources.

Greaves' cluelessness paper was published in 2016. My impression is that the broad argument has existed for 100+ years, but the formulation of cluelessness arising from flow-through effects outweighing direct effects (combined with EA's tending to care quite a bit about flow-through effects) was a relatively novel and major reformulation (though probably still below your bar).

This post itself is a major insight since 2015! :P