my issue with this is that the harness IS the training environment
when OpenAI ships Codex or Anthropic ships Claude Code, they're not chasing app-layer revenue, they're building the surface they need to RL the next model on agentic behavior
opencode and t3code don't generate the trajectories that feed post-training
"core competence" was a 2023 frame. in 2026 the model and the scaffold co-evolve.
whoever owns the loop owns the next generation
just my 2 cents
i'm strongly against model companies focusing too much on harness, but i would love to hear if anyone has a strong argument for it
my reason against it:
if openai didn't build GPT 5.5, no one else can. this is their core competence
if openai didn't build codex cli and app, we have opencode and t3code. building harness is NOT their core competence
this is not saying products like claude code, codex aren't good - i genuinely think these are top tier products built by really talented people
my point is - the world might be a better place if model companies focus more on their core capability and give us better, faster, safer and cheaper models, rather than competing with the ecosystem in the application layer
what do you think?