Good news: the latest LM Studio update changed the exposed API to remove the harmony tokens and reasoning blocks, no you can run gpt-oss against opencode.
OK initial impressions of gpt5 in opencode
it works - it's calling tools, it's persistent, it's doing the right thing
it's cheaper than sonnet4 and potentially better - looks like we might have a new detault
we polished up our agents feature and it's real nice now
- built in build/plan agents
- tab to switch primary agent
- @ mention to create subagent
- automatic agent triggering
simple config to make any combination of models, prompts, tools, whatever works for your workflow