Configuring *correct* Context size for OpenAI models in Opencode CLI

Wrong max context size

Hello,
As far as I am aware, OpenAI models such as Luna, Terra and Sol on the Plus subscription have a context size of 270k. However, Opencode CLI assumes that these models have a 500k context size.

I used /connect in Opencode (1.18.16) to connect to OpenAI via my Plus subscription.

How do you ensure that Opencode uses the correct context size? For 250k tokens it should not be assuming that it has used only 50% of the available context.
Surely, for such common models from OpenAI, it should be able to identify and set this correctly without the user having to make manual changes in config.json.

What am I missing?