GLM-5.x and Kimi 3.x are good open weight models. In theory one could run them locally if the prices of the DGX/Halos ever come back down (you use to be able to run them on ~$20k worth of hardware, but now it looks like you need $40k worth of hardware after all the recent price jumps. Gorgon Halo and newer memory offloading techniques might change that).

With OpenCode you can run /model and just select whatever your provider offers. I always recommend not using prompts. Create an AGENT.md with your project rules, then create a plan/01-initial-requirements.md. Write an entire requirements spec. Commit those. Then tell the LLM "Read AGENT.md for project rules and run plan/01-initial-requirements.md".

That way you can commit that output on a branch, jump back to the original commit, and run the plan again with a different model. You can do that multiple times and compare the output on all the branches. Some models might give you better UI, some better structure. You can just keep the one you like most, or ask a model to combine certain aspects of each branch into your final.