You can evaluate the compatibility of shared prompts across two LLM APIs by comparing their outputs on identical inputs using similarity metrics.
Here is the code snippet below:

In the above code we are using the following key points:
- 
OpenAI's API to generate a response from GPT-based model. 
- 
A generic POST request to call another LLM via its API endpoint. 
- 
SequenceMatcher to compute textual similarity between both responses. 
Hence, this method enables a practical comparison framework to assess prompt behavior consistency across multiple LLM platforms.