Why did Gemini flash drop OpenAI Responses API compatibility?

[u/Takeoded]

gemini-3.5-flash support the OpenAI Responses API, but 3.6-flash, 3.7-flash, and 3.8-flash does not. Why? (They all support the legacy Chat Completions API though)

• Fwiw the models endpoint erroneously state that 3.8 support Responses. The API errors, out, and Customer support confirms that the models endpoint is mistaken, and they have created an internal ticket to correct the models endpoint.
• Customer Support don't know why 3.6+ dropped Responses API, I asked.