The best AI models for legal work, compared.
Contract review, discovery, memos, research. Which frontier model to trust for which task — and how to run any of them without leaking privileged data.
AI model choice in legal, done properly.
Every large-firm AI evaluation ends in the same conclusion: no single model wins on every legal task. Claude excels at long-document reasoning. GPT-5 is decisive on structured drafting. Gemini's 2M-token window ingests entire deal rooms. Perplexity cites its sources. The right answer is run all of them and compare — not standardize on one and hope.
The bigger problem is confidentiality. A prompt containing client names, matter numbers, or privileged material sent to any public LLM is a Model Rule 1.6 problem. Backplain's AI Firewall redacts those elements before the prompt reaches the model — so your team gets multi-model comparison without the risk profile.
Which frontier models fit this work.
| Model | Best for | Context | Hosting profile |
|---|---|---|---|
| Claude Sonnet 4.5 | Contract review, long-doc reasoning, careful drafting | 1M tokens | Closed API · behind AI Firewall |
| Claude Opus 4 | Statute reasoning, nuanced analysis, brief writing | 200K | Closed API · behind AI Firewall |
| GPT-5 | Decisive drafting, structured memos, code-like clause logic | 400K | Closed API · behind AI Firewall |
| Gemini 2.5 Pro | Full deal-room ingestion, multimodal exhibits | 2M | Closed API · behind AI Firewall |
| Perplexity Sonar Pro | Cited legal research, current-events check | 200K | Closed API · web-grounded |
| Llama 4 Scout | Air-gapped or sovereign matters, ITAR-adjacent work | 10M | Open weights · Sovereign Compute |
Recommendations reflect current model behavior; run the Tokyo Test on your actual documents to confirm which model wins for your specific matter.
Contract & clause review
Load the master agreement, ask three models to flag deviations from your playbook. Where they agree, you're clear. Where they disagree, that's the clause to read yourself.
Discovery triage
Run privileged-material classification through Claude Sonnet 4.5 and GPT-5 in parallel; escalate disagreements to a human reviewer.
Memo & brief drafting
Draft in Claude Opus for nuance, sanity-check in GPT-5, cite-check in Perplexity. All in one workspace.
Deposition & transcript analysis
2M-context Gemini ingests full transcripts; parallel Claude call surfaces the inconsistencies a single model would smooth over.
Model Rule 1.6 (Confidentiality). The AI Firewall satisfies duty-of-care requirements by preventing client-identifying data from crossing the model boundary. Every prompt is logged for audit at the seat level.
Privilege. Redaction is deterministic and reversible only inside your tenant. No prompt or output is used for model training by upstream providers.
Data residency. EU-residency models (Mistral Large 2, Codestral) are available for matters requiring GDPR-strict processing. Sovereign Compute offers full single-tenant deployment for ITAR-adjacent or sealed matters.
The Legal AI Model Guide
A one-page cheat sheet: which model to use for which legal task, and where the AI Firewall matters most. Sent to your inbox.
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Run the Tokyo Test on your own legal documents.
Three free multi-model prompts. No signup.