What’s the biggest short-term efficiency you’ve been able to achieve within your IT department via generative AI?

Nothing as such in short term. 

Efficiency gains in Software Development > 10%
When it comes to AI in general: We use AIOps for the Monitoring / Observability. There we are able to detect problems earlier and the analysis of problems is much easier.  

Not yet achieved, but in flight. I have a client who has internally developed their own app over 10 years. Due to the pace they have moved the documentation has not been done.

The cost to document that manually is significant, so we are exploring using an LLM to see if it can cut down that cost.. 

We're running it as an experiment, with three possible outcomes:

1. It is able to fully document the code base
2. It is able to partially document the code base, but will need some manual tweeking
3. It is not able to document it at all. 

If it's 1 then it's a long term efficiency gain, 2 would be short term. 3 is still a success as means we are no worse off than today. 

As we work in a highly regulated industry, our Risk Management team has taken the position that we will not use Generative AI at this time.  The continued reporting of errors, issues, and biases in the models suggests that this is a reasonable approach.  On a more direct, personal level, I struggle to understand the desire to outsource critical thinking.  It's a dangerous move from a competitive standpoint, IMHO.