Claude Opus 4.7 scores 90.9% on BigLaw Bench while GPT-5.4 sits at 84.2%. That's not a rounding error -- it's the difference between a draft your senior partner redlines twice and one that goes out with minor tweaks. At $5/M input tokens vs OpenAI's $7.50/M, Claude also costs less per document.

But GPT-5.4 isn't losing this race everywhere. OpenAI's ecosystem -- plugins, DALL-E, browsing, Code Interpreter -- gives it versatility Claude can't match yet. If your firm needs one tool for everything from contract drafting to financial modeling to client-facing image generation, GPT-5.4 covers more ground. The question isn't which model is "better" -- it's which workflow your firm actually runs.

Claude Opus 4.7 was built for extended reasoning and instruction following. On legal writing benchmarks, it produces output that reads like it came from a mid-level associate -- proper citation format, consistent defined terms, appropriate hedging language. The self-verification feature catches its own hallucinations before you see them.

GPT-5.4 writes competently but tends toward generic phrasing. It'll give you a solid first draft, but you'll spend more time on voice and precision. Where GPT shines is speed on shorter tasks -- quick email drafts, client summaries, research memos under 500 words. For anything over 2,000 words with complex structure, Claude pulls ahead noticeably.

Pricing Breakdown for Law Firm AI Budgets

Claude Opus 4.7 runs $5/M input tokens and $25/M output tokens. GPT-5.4 charges $7.50/M input and $30/M output. On a typical 15-page contract review generating ~4,000 tokens of analysis, that's roughly $0.10 with Claude vs $0.12 with GPT. Negligible per document.

But scale it. A mid-size firm reviewing 200 contracts/month with iterative prompting (3-4 rounds per doc) hits ~3.2M tokens monthly. Claude saves ~$8,000/year on that workflow alone. The real cost difference isn't per-query -- it's per-workflow at volume. Both offer team plans at $25-30/seat/month for the chat interfaces, where the pricing gap narrows.

Where GPT-5.4 Still Beats Claude for Lawyers

Three areas. First, ecosystem breadth. GPT-5.4 connects to Excel via Code Interpreter, browses the web natively, generates images, and runs custom GPTs your paralegals can use without prompting skills. Claude's tool ecosystem is growing (Word integration launched Q1 2026) but isn't there yet.

Second, voice mode. GPT-5.4's voice interface lets attorneys dictate and get responses in real-time -- useful for mobile attorneys or during depositions prep. Claude doesn't have a comparable voice product.

Third, institutional adoption. If your firm already runs Microsoft 365, GPT-5.4 integrates through Copilot's backend. Adding Claude means adding a second vendor, a second security review, a second training cycle.

Extended thinking mode lets Claude reason through multi-step legal analysis without losing the thread. Ask it to identify every indemnification obligation across a 50-page MSA, cross-reference them with the limitation of liability clause, and flag conflicts -- Claude handles that in one pass.

The 1M token context window means you can feed it an entire deal room. GPT-5.4's 128K window forces you to chunk documents, which breaks cross-reference analysis. For M&A due diligence, litigation document review, or regulatory compliance mapping, Claude's context window isn't a nice-to-have -- it's the reason the output is usable.

Claude Enterprise's zero-retention policy and BAA availability also matter. For firms handling privileged communications, Claude's data architecture is cleaner than OpenAI's current offering.

Which Model Should Your Firm Choose in 2026

If your practice is document-heavy (corporate, real estate, insurance defense), Claude Opus 4.7 is the better investment. The writing quality, context window, and cost-per-token math all favor it.

If your firm needs a Swiss Army knife -- drafting plus financial modeling plus presentation building plus client communication -- GPT-5.4's ecosystem does more out of the box. Especially if you're already a Microsoft shop.

The smartest firms aren't choosing one. They're running Claude for substantive legal work and GPT/Copilot for operational tasks. That hybrid approach costs ~$55/seat/month but eliminates the compromise.

The Bottom Line: Claude Opus 4.7 writes better legal documents at lower cost; GPT-5.4 does more things across your firm's tech stack -- the best firms use both.

AI-Assisted Research. This piece was researched and written with AI assistance, reviewed and edited by Manu Ayala. For deeper takes and the perspective behind the research, follow me on LinkedIn or email me directly.