Evan Troxel closed Arc 2 of his Next AEC Tech Stack series last week with an episode called Who Signs When the AI Is Wrong? I got the last word, and it was about money.
If work that used to take 100 hours now takes 70 because AI helped, and you bill by the hour, you've handed those 30 hours to the client. The practice did the work of changing how it works. The client got the saving.
None of this is new. Every wave of AEC technology has come with a tax.
BIM brought Revit licences, BIM managers, coordinators and interoperability consultants. Practices paid for all of it, and most of the cost moved to a new line item rather than coming back as margin.
AI is shaping up the same way. Subscriptions. Workflow consultants. Someone in the office who now owns the prompts. Same tax, new invoice.
This time some of the gains are already visible. Not the multi-agent story, which is still mostly demos running ahead of what practices can absorb. But documentation automation and constraint-based early design are working now. That makes the billing question sharper. A practice on hourly fees pays the new tax and gives away the gain. Both at once.
I'm not arguing the client should get none of it. A service is worth more than the hours it takes, and some of the gain should be shared. Clients will ask for it anyway. The question is whether the practice decides how much to share, or whether the billing model decides for it.
Michael Jansen of TwinMaster put it another way on the same episode. A fee is time-bound. When the job's over, the fee is gone, and you're on to the next one.
The place to start is an honest time audit, service by service. Where has AI already changed what it costs you to deliver? Not where a vendor says it will. Where it has, on your projects, with your people.
Hourly billing exists for a reason. It's a way of covering risk. If something takes longer than expected, you're covered, or you should be.
AI starts to change that on parts of a project. Take the early work of reading the local planning requirements and working out what you can and can't do on a site. If AI is doing that reading and saving hours of research, the risk comes down with the hours. That's when you can be comfortable putting a fixed fee on that part of the job.
Where the audit shows that, reprice. Leave everything else as it is until it says otherwise.
There's a tell. The practices spending hours on AI hero renders are often the same ones that haven't touched their fee structures or contract terms. Making a still image look better is the easy use of AI. Changing how you charge for the work is the hard one, and the renders are a way of not having that conversation.
The firms doing the audit now will have their own numbers when the question comes up. The ones that wait will still have the conversation. They just won't be the ones who started it.
*The full episode is here.