Question: Any plans to make the specification more OpenAI compatible ?

### Is your feature request related to a problem? Please describe.

Unnecessary message conversations because of different schemas.

### Describe the solution you'd like

I know, it's probably weird to ask, but I saw that Google have an OpenAI compatible specification, can we use this for the messages structure instead of the parts API ?

It's probably a huge breaking change, but better early then never :)

Frankly when I look on the schema of most providers they have the messages following one spec.
The spec of Google is just different with message parts - IMO it creates unnecessary overhead and computation when I want to integrate the project not just with Gemini LLMs.

To give you an example:

I might want to submit a task to an A2A server that has an LLM, that LLM doesn't necessarily have to be a Gemini one, then if I want to interact with other vendor's API's I have to convert the messages before sending them to their API (most of them use OpenAI compatible spec).

### Describe alternatives you've considered

I think it could be way simpler if we just use the same spec or maybe in a future ADK / SDK introduce a message conversation as a util that people could use for language processing with other LLMs. WDYT ?

### Additional context

Goal is, having a vendor agnostic and broader compatibility.

### Code of Conduct

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