The frontier labs were already bored of math contests by the 2025 Putnam, and they will certainly not bother with IMO 2026. I could imagine that some formalization startup might still try pursue a Lean-verified IMO perfect score, which has not been accomplished yet ... but I hope they don't -- we all know that Codex/Claude could do this easily, so please just leave the spotlight to the students.
As for research math: it appears the only frontier labs pushing this have been OpenAI and Google DeepMind. My guess from observing OpenAI is that they use Erdos problems (only) as some kind of internal benchmark, but they do not try to benchmax and they only release solutions that are sufficiently interesting. DeepMind is a different beast, which pursues math and science applications for their own sake and will likely continue doing so.
I think there will also continue to be a space for startups to do research math things. They're not expected to make revenue for a while, and they can find some story to spin to VCs about why it will eventually be profitable.