Billing for AI-Assisted Legal Work

AI compresses drafting time. Most engagement letters still price that time by the hour. When Claude drafts a motion in 12 minutes that used to take three hours, what does a defensible bill look like?

The answer depends on your engagement agreement, the principles in ABA Formal Opinion 512 (February 2024), and your state bar's rules. This is practical guidance, not a formal ethics opinion. Attorneys should verify applicable rules with their specific bar before modifying billing practices.

What ABA Formal Opinion 512 Actually Says

ABA Formal Opinion 512 (February 2024) addresses attorneys' ethical obligations for fees, disbursements, and surcharges. While not written specifically about AI, its principles apply directly when structuring fees for AI-assisted work. Four points from that opinion shape everything that follows.

Learning time is not billable. Attorneys may not charge clients for time spent learning to use AI tools. The reasoning is consistent with existing doctrine: a client does not pay for a lawyer to become competent in a tool the lawyer chose to use. This applies to prompt engineering learning curves, reading AI vendor documentation, and general AI orientation time. It does not mean AI-assisted work time is unbillable; it means the learning overhead is an overhead cost.

Competence now includes AI. The duty of technological competence under Model Rule 1.1, Comment 8, covers staying current with the benefits and risks of relevant technology. That extends to generative AI. An attorney who uses AI tools without understanding their limitations and failure modes has a competence problem, not just a billing problem.

Rule 1.5 applies to AI efficiency gains. This is the billing rule most directly at stake. Rule 1.5 prohibits clearly excessive fees. If generative AI compresses a task that previously required six hours of attorney time down to 45 minutes, charging the six-hour historical rate raises a Rule 1.5 question. The opinion does not say the work has zero value. It says the fee must be reasonable given what was actually done.

Disclosure when asked. The duty of communication under Model Rule 1.4 requires candor with clients about the means used to accomplish their work. If a client asks whether AI was used in their matter, answering honestly is not optional. Beyond that reactive baseline, proactive disclosure through engagement letters is the safer posture and is becoming the expected standard among careful practitioners.

State Bar Guidance: Check Your Jurisdiction

Several state bars have issued AI ethics opinions alongside or ahead of the ABA's guidance. California, Florida, and New York have published relevant materials, and more are in process. State guidance can go further than the ABA's floor and may address specific practice contexts, court filing rules, or fee arbitration standards.

Relying on the ABA opinion alone is a risk. Your state bar may have more specific rules, and some have moved faster than the ABA on AI-related disclosure and billing questions. Check your jurisdiction's AI guidance at least annually, and any time you materially change how your firm uses these tools.

Three Billing Structures That Work

The question is not whether to use AI. The question is how to structure billing so that AI use is both ethical and economically rational for the firm.

Value Billing

Fixed-fee and value-based arrangements decouple payment from hours entirely. The client pays for the deliverable, not the time. AI efficiency directly benefits the firm's margin without any billing ethics problem, because the fee was agreed to in advance based on the value of the work product, not hours projected.

This model works best for predictable matter types: standard contract review, routine corporate filings, form-based transactional work, personal injury demand packages. (For a detailed workflow on that last category, see how to write a demand letter with Claude AI and the companion PI demand letter template.) It requires a careful intake process to scope the work accurately. Once you have a fixed fee agreed to, AI speed is pure upside.

Adjusted Hourly Billing

If your practice remains hourly, bill the actual time spent on AI-assisted work: attorney review, editing, and supervision. If you spend one hour reviewing and substantially editing a Claude-drafted motion, you bill one hour of attorney time. The time entry reflects the actual legal work performed, and that is consistent with the Rule 1.5 analysis.

What this means operationally is that AI does not just disappear from time records. It changes the composition of time entries. Drafting time may drop; review and refinement time stays. The total hours on a matter may decrease, which is a benefit to the client. Firms that communicate this proactively tend to earn more goodwill than those that quietly absorb the efficiency gain without mention.

Efficiency Premium Through Fixed Engagement Terms

A hybrid approach is to establish a fixed fee for a deliverable in the engagement letter, with the fee reflecting the value of fast, high-quality output. A client who needs a 48-hour turnaround on a complex contract review may pay more for speed than for the same work delivered in two weeks. The engagement letter captures that premium without connecting it to hourly rate math.

The client is buying certainty and speed, not hours. AI is the mechanism that makes speed possible. The fee is agreed to upfront, so there is no Rule 1.5 question after the fact. The same structure works well in settlement matters, where speed and output quality are equally at a premium. See the Claude AI settlement negotiation protocol for a detailed workflow.

What You Cannot Do

Three practices will get you in trouble under existing guidance.

Billing AI tool subscription costs as a disbursement without prior client consent is not defensible. An AI subscription is an overhead cost of operating a modern practice. Passing it to the client requires the same disclosure and consent as any cost allocation, and that agreement belongs in the engagement letter before work begins.

Billing historical hours when AI has materially shortened the actual work is the most direct Rule 1.5 problem. If the rate was set based on the assumption that drafting a brief takes 12 hours, and AI makes it three hours, billing the phantom nine hours is a fee that is no longer tied to the work performed. Opinion 512 is explicit on this point.

Concealing AI use from a client who asks is a candor problem under the Model Rules, not just a billing problem. The duty of communication under Rule 1.4 and the prohibition on misrepresentation under Rule 8.4(c) both apply. This is not a close call.

The Engagement Letter Clause

The cleanest way to avoid billing disputes is to address AI use before the engagement begins. Here is a practical model clause:

Our firm uses AI-assisted tools, including large language models, to support legal research, drafting, and document review. All AI-generated work is reviewed, edited, and supervised by a licensed attorney to verify accuracy and apply professional judgment. We do not bill clients for time spent learning to use AI tools. Fees for AI-assisted work reflect actual attorney time spent on supervision, review, and client-specific judgment. Any costs associated with AI tools are absorbed by the firm as overhead unless separately disclosed and agreed to in writing.

Adjust the specific terms to match your billing model. The goal is to eliminate ambiguity before a dispute arises, not to litigate intent after a bill is challenged.

Putting It Into Practice

The firms billing AI-assisted work correctly are not waiting for perfect clarity from the bar. They are making reasonable, documented choices aligned with existing rules, disclosing AI use proactively, and structuring their billing around what they actually did rather than what the old hourly model assumed they would do.

Module 8 of The Leveraged Attorney covers billing for AI-assisted work in depth, including a walkthrough of Opinion 512, a survey of state bar variations, and engagement letter templates you can adapt directly. It is built for practicing lawyers, not law students, and it skips the classroom hypotheticals in favor of what actually shows up in billing disputes.

The efficiency advantage AI creates is real and it is substantial. The attorneys who benefit most from it are the ones who have already thought through the billing structure, gotten their engagement letters right, and positioned AI speed as a client benefit rather than a liability to manage.

This article is for educational purposes and does not constitute legal ethics advice. Rules on attorney billing, AI use, and fee agreements vary by jurisdiction and are evolving. Attorneys should review their specific state bar's guidance and consult ethics counsel when modifying billing practices related to AI use.