Which AI Model Should I Use?
What Are AI Models?
AI models are like brains trained to do a specific kind of thinking. Each model has different strengths.
Few examples include:
GPT-4.1 (OpenAI) is great at complex reasoning and long legal texts.
GPT-4.1 Mini is cheaper and faster, good for summaries and quick answers.
Sonar Pro (Perplexity) is trained for real-time, high-quality web-based Q&A.
Mistral OCR focuses on extracting text from scanned documents or images.
Think of models like different legal assistants—some are great at deep legal research, others at drafting, and some just scan and extract facts from a document.
AI models are like specialized brains trained to perform specific types of thinking or tasks. Some are excellent at understanding complex legal reasoning, while others are optimized for speed, summarization, or text extraction. For example, GPT-4.1 is designed for deep analysis and long documents, whereas GPT-4.1 Nano is lightweight and ideal for high-volume tasks like clause tagging. Models like Mistral OCR focus on reading scanned documents. This specialization exists to balance cost, speed, and performance—no single model fits all use cases. Choosing the right model means selecting the best brain for the job, depending on the complexity and goals of your task.
Lexemo’s e! integrates some of the world’s most advanced AI technologies — but with so many options, it can feel overwhelming. This guide breaks down the different models offered by OpenAI, Perplexity, and Mistral — and helps you decide which one to pick for your task.
OpenAI Models
GPT-4.1
GPT-4.1 is OpenAI’s most advanced language model, designed for tasks that require deep reasoning, precision, and understanding of complex language. In legal workflows, it excels at interpreting nuanced regulations, analyzing long contracts, and following multi-step instructions with high accuracy.
Its ability to maintain context across large volumes of text makes it ideal for reviewing detailed legal documents or cross-checking clauses across agreements. While it comes at a higher cost, GPT-4.1 delivers unmatched quality and reliability, making it the best choice when legal precision and thoroughness matter most. If your task is critical and complex, this is the model to trust.
Use it when: You need top-tier reasoning and understanding. Ideal for complex legal questions, detailed contract reviews, or multi-step instructions.
Strength: Most powerful and accurate model available.
Cost: Higher
Best for: Complex legal research, document analysis, clause cross-checking
GPT-4.1 mini
GPT-4.1 Mini is a lighter, faster, and more cost-effective version of GPT-4.1, designed to handle common legal tasks without compromising too much on quality. It strikes a smart balance between performance and efficiency, making it ideal for day-to-day legal work like summarizing contracts, drafting standard clauses, or reviewing less complex documents.
While it may not offer the same depth as the full GPT-4.1, it is still highly capable and responsive. Especially useful in interactive tools or scenarios that require quick turnaround. For legal professionals seeking reliable results at a lower cost, GPT-4.1 Mini is a practical and versatile option.
Use it when: You want good performance without the high cost. Great for general drafting and summarizing legal docs.
Strength: Balanced accuracy and speed
Cost: Medium
Best for: Summarizing contracts, creating legal checklists, client memos
GPT-4.1 nano
GPT-4.1 Nano is the fastest and most lightweight version of the GPT-4.1 family, optimized for high-speed processing and low-cost operations. It’s perfect for repetitive, large-scale tasks such as tagging clauses, classifying document types, or extracting key data points from hundreds of legal files.
While it lacks the depth of reasoning found in larger models, its strength lies in handling structured, rule-based tasks with efficiency.
GPT-4.1 Nano is ideal when you need scale and speed—such as processing bulk contracts or invoices—without a heavy price tag. For routine legal operations, it delivers speed, affordability, and consistent performance.
Use it when: You need to process a lot of documents quickly. It’s fast and efficient, but less detailed.
Strength: High-speed for repetitive tasks
Cost: Low
Best for: Tagging document types, extracting simple info, classifying files
O3 mini & O1 mini
O3 Mini is a streamlined model optimized for fast, responsive interactions with good contextual understanding. It performs well on everyday legal tasks such as generating first drafts of contracts, answering standard legal queries, or formatting legal documents. It offers a solid balance between cost and quality, making it suitable for tasks where you need decent legal language handling without the depth of full-scale models.
O3 Mini is ideal for interactive bots or client-facing tools where speed and clarity matter. It’s best used for moderately complex workflows that benefit from quick and accurate output at a reasonable cost.
O1 Mini is the most basic and efficient model in its tier—focused on simplicity, speed, and affordability. It works well for lightweight tasks such as extracting metadata, identifying document types, or generating boilerplate text.
While not suited for deep legal analysis, it’s perfect for high-volume automation tasks where accuracy can be guided by templates or rules.
O1 Mini shines in situations where cost-efficiency and consistency are more important than nuance, such as populating standard contract fields or performing initial triage of legal documents.
Use it when: You’re building a bot that needs to respond fast — like a chatbot.
Strength: Quick and responsive with decent quality
Cost: Low to medium
Best for: Interactive tools, quick Q&A, internal policy chatbots
Text-embedding-ada-002
Text-embedding-ada-002 is not a chatbot or generative AI model like GPT—it’s an embedding model. Its job is to convert text into numerical vectors that capture the meaning of the content. These embeddings are used in search, classification, similarity detection, and semantic clustering.
In legal workflows, it powers features like:
Semantic search (e.g., “Find me similar NDAs”)
Document clustering (e.g., grouping contracts by topic)
Contextual memory in retrieval-augmented generation (RAG) systems
It’s extremely fast and cost-efficient, making it ideal for large-scale document databases. Think of it as the “under-the-hood” intelligence that lets your platform understand legal content beyond keywords—and retrieve the right information even if the wording is different.
Use it when: You’re using RAG (retrieval augmented generation). It helps AI “search” through your documents and answer based on them.
Best for: Legal assistants that answer based on case law or internal documents
Perplexity AI Models
These models are great at reasoning and pulling insights, especially from longer or more nuanced content.
Sonar Reasoning Pro
Sonar Reasoning Pro is Perplexity AI’s most advanced model, built specifically for real-time reasoning and web-connected tasks. It combines high-quality language understanding with access to live web data, making it exceptionally powerful for up-to-date legal research, current case tracking, and cross-referencing recent regulations or news.
This model excels when:
You need accurate answers with current context (e.g., new rulings or amended laws)
You’re working with open-ended legal queries requiring thoughtful reasoning
You want an AI assistant that cites sources in real time
Sonar Reasoning Pro is best suited for tasks where truthfulness, current knowledge, and clear citations are essential. While more expensive than basic models, it’s perfect for legal professionals who need timely and reliable results with clear traceability.
Use it when: You need the AI to go deeper — for example, comparing two clauses or explaining risks
Best for: Risk analysis, scenario evaluation, strategic comparisons
Sonar Pro
Sonar Pro is Perplexity AI’s advanced model built for real-time, web-connected research. It excels at delivering accurate, up-to-date answers with clear source citations, making it ideal for legal research, academic writing, and market intelligence.
With a large context window (up to 200,000 tokens), it handles long, complex queries and follow-ups with ease. What sets it apart is its focus on factual precision and web access, rather than deep reasoning.
Compared to Sonar Reasoning Pro, which specializes in multi-step logic and structured problem-solving, Sonar Pro is your go-to for current, citation-rich responses rather than complex analytical tasks.
Use it when: You want high-quality responses without the premium cost of GPT-4.1
Best for: Legal bots, summarising case law, building a document assistant
Sonar
Sonar is the standard AI model from Perplexity—fast, reliable, and optimized for general-purpose tasks like answering questions, summarizing content, or providing citations based on both training data and current web information. It offers a solid performance baseline, making it ideal for routine tasks that don’t demand high-level reasoning or deep legal analysis.
Unlike its more powerful siblings—Sonar Pro and Sonar Reasoning Pro—the basic Sonar model is faster and more cost-efficient, designed for everyday use cases (e.g., quick legal summaries or fact-checking) or, capable of web search, but with less depth and nuance in answers
Choose Sonar when you want reliable responses at speed and scale, and don’t need multi-step reasoning or advanced legal insight
Use it when: You want a fast, general-purpose model
Best for: Standard drafting tasks, FAQs, client chatbots
Sonar Reasoning
Sonar Reasoning is Perplexity’s mid-tier model designed for more thoughtful and structured answers than the standard Sonar. It introduces basic chain-of-thought reasoning, enabling the model to break down complex queries into logical steps. This makes it well-suited for legal workflows that involve conditional logic, interpreting layered regulations, or drafting based on context.
Compared to Sonar, it delivers deeper and more accurate responses, especially for multi-layered prompts.
Use it when: The task requires more “thinking” than just answering – such as risk ratings or contract assessments
Mistral AI Models
Mistral OCR
Mistral OCR is a specialized AI model designed to extract text from scanned documents, and PDFs using Optical Character Recognition (OCR) technology. It’s particularly useful for digitizing legal documents, invoices, contracts, or handwritten notes—turning unstructured visual content into searchable, structured data.
Unlike standard language models, Mistral OCR focuses on accurately identifying characters, layouts, and formatting from various document types, even when the quality is suboptimal. It’s ideal for automating data entry, archiving legal records, or feeding extracted text into AI workflows. Mistral OCR adds real value in legal environments that deal with large volumes of physical or scanned content.
Use it when: You upload scanned documents and want the AI to read and extract the text.
Best for: Reading scanned invoices, contracts, or documents with tables
So, Which One Should I Use?
Tip for e! Users
You don’t need to know everything about AI models to start using them effectively. Begin with a simple model for basic tasks, and switch to more powerful options as your needs grow. The key is experimentation—test, tweak, and learn which model fits your workflow best. Whether it’s for summarizing, extracting, or drafting, the right model often depends on the task, not just the specs.
As a user of e!, you don’t have to pick the perfect model from the start. e! makes it easy to test your automation with different models. Start simple. If you need deeper understanding or better formatting, try a more advanced model.
Need help deciding? Reach out to our team or explore sample bots in e! for inspiration.