How should a law firm bill for AI assisted work?

The rule that governs it is older than the technology and it has not moved: a fee has to be reasonable, and a lawyer bills for time actually spent rather than for time a task used to take. The American Bar Association addressed generative AI and fees directly in Formal Opinion 512 in 2024, and state guidance continues to arrive with differences on the points that decide the answer, so the applicable rule depends on the jurisdiction and the engagement letter rather than on anything a vendor says. What follows from the rule is practical: a product that turns six hours of review into one has changed the invoice, not only the workflow, and somebody has to be able to show which work the software did. That is where the market is quiet. Of 149 legal AI vendors recorded by the AI Legal Index, 117 advertise time savings in public material while publishing nothing about how that time should be treated on a bill, 0 publish both a per matter record of AI assisted work and guidance on billing or fee treatment, 8 emit a usable record with no fee guidance attached, and 24 address none of it.

The decision belongs to the firm and the rule that governs it belongs to the jurisdiction, so this page does not tell anyone how to bill and is not a substitute for the guidance that binds them. What an index can do is answer the part the guidance leaves open, which is whether the software makes an honest answer practical. Three published records decide that: whether the product can show what it did, whether the vendor has said anything about how to treat it, and whether the price is knowable without a sales call. The index records all three on every vendor.

Not by asking anyone to remember. A firm that wants to bill accurately for AI assisted work needs the work identified at the matter level, which means the product recording what it did, when, and against which matter, in a form that survives into a time entry or an invoice narrative. 8 of 149 vendors emit a record of that kind: Anaqua, Brightflag, Counsel Stack, InPractice, Legal Tracker, Mitratech, SimpleLegal and Vesence. Of those, 0 also publish guidance on how to treat it on the bill, which is the harder half, because it requires the vendor to have an opinion about its customer's revenue. The remaining 141 vendors leave the firm to reconstruct AI involvement after the fact, from memory, at the point where a client is asking why an entry says four hours.

A per matter record of AI assisted work is built for the invoice, and it turns out to be the artifact a court asks for too. A growing number of judges require filers to state whether generative AI was used and to certify that citations were checked by a person, which means knowing which model produced which passage and who verified it. 1 of 149 vendors export a document level record covering all of that, 84 produce part of it, and 0 vendors satisfy both uses with the same record. The certifying signature belongs to the lawyer in both cases. The difference is whether the evidence behind it takes two minutes to produce or has to be rebuilt from memory under a deadline.

How to bill. That depends on the jurisdiction, the engagement letter, the client and the matter, and it is not a question an index answers. Nothing here is legal advice or fee advice. A vendor publishing nothing about billing treatment is a statement about that vendor’s disclosure and not about anyone’s compliance, and a vendor that publishes guidance has not thereby made any particular invoice reasonable.

The records reach only as far as public material, and an absence is dated: not located in public sources on the date shown, redated the day the vendor publishes. The reason the published position still matters is the one that runs through this whole index. A procurement call leaves no artifact, and an artifact is what a firm forwards to a client who has asked, reasonably, what the software did and what it cost.