Hands-On with Claude Opus 4.6 vs Gemini 3 Pro vs GPT-5.2

The AI landscape is evolving at a blistering pace. Within months, we've seen Anthropic release Claude Opus 4.6, Google launch Gemini 3 Pro, and OpenAI push out GPT-5.2. Each claims to be the best. But which one actually delivers for engineering workflows?

I put them to the test with a real use case: building a product prototype from scratch using just 3 prompts.

The TL;DR

Before we dive deep, here's the quick summary:

What Makes Opus 4.6 Different?

Claude Opus 4.6 isn't just an incremental update—it's a focused upgrade for long-running knowledge work, agentic coding workflows, and enterprise productivity tasks.

The Benchmarks Don't Lie

Let's look at how these models compare across key areas. I'm using the official benchmarks from Anthropic, Google, and OpenAI's announcements.

Key Benchmark Highlights

Claude Opus 4.6:

• 68.8% on ARC AGI 2 (novel problem-solving)—outperforming GPT-5.2 Pro (54.2%) and Gemini 3 Pro (45.1%)
• 90.2% on BigLaw Bench for legal reasoning
• 1606 Elo on GDPval-AA, beating GPT-5.2 by ~144 Elo points

Gemini 3 Pro:

• 81% on MMMU-Pro for multimodal understanding
• 91.9% on GPQA Diamond for PhD-level reasoning
• 1501 Elo on LMArena Leaderboard

GPT-5.2:

• 100% on AIME 2025 for mathematics
• 93.2% on GPQA Diamond (highest for graduate-level reasoning)
• Perfect accuracy up to 256k tokens on MRCR v2

The Full Comparison Table

Here's the comprehensive benchmark comparison:

My Real-World Test: 3-Prompt Product Prototype

Theory is nice, but I wanted to see how these models perform in a real engineering workflow. I built a minimal product prototype—a simple SaaS dashboard—using exactly 3 prompts with each model.

Using Opus 4.6 Inside Claude Code & VS Code

I tested Opus 4.6 through Claude Code CLI and the Continue extension in VS Code. Here's what I observed:

Claude Code CLI

The new agent teams feature is incredible. I could spin up sub-agents for:

• Backend API scaffolding
• Frontend component generation
• Test writing

All running in parallel. The main agent coordinated results and merged them intelligently. For complex refactoring tasks across multiple files, this is a productivity multiplier.

VS Code Integration

Using Opus 4.6 via the API in VS Code extensions, the model maintained context across my entire project. I could ask questions about files I hadn't opened in hours, and it remembered the architecture decisions we'd made together.

The 1 million token context window means I can feed it my entire monorepo and ask complex cross-cutting questions without summarization hacks.

When to Pick Each Model

Based on my testing and the benchmarks, here's my recommendation:

Choose Claude Opus 4.6 If:

• You work with long documents (contracts, research papers, full codebases)
• You need financial modeling or Excel automation
• You want agentic coding workflows with multiple parallel tasks
• You prioritize minimal follow-ups to get production-ready output
• You work in legal, finance, or enterprise contexts

Choose Gemini 3 Pro If:

• You need multimodal understanding (images, video, audio + text)
• You work on research tasks requiring deep reasoning
• Speed and cost-effectiveness are priorities
• You're building creative applications that mix media types

Choose GPT-5.2 If:

• You need the broadest ecosystem integrations (Microsoft/Office, Copilot)
• You work with vision-enabled agentic pipelines
• You need tool-calling orchestration across many services
• Mathematical reasoning is core to your workflow

The Bottom Line

Claude Opus 4.6 represents a meaningful leap for professional knowledge work and agentic coding. It's not just marginally better—it fundamentally changes how you can structure AI-assisted development workflows.

The agent teams feature in Claude Code is worth the upgrade alone. Combined with the 1M token context and improvements in finance/legal benchmarks, Opus 4.6 is positioned as the go-to model for serious engineering work.

Gemini 3 Pro remains unmatched for multimodal synthesis, and GPT-5.2 offers the most mature ecosystem. But for pure coding productivity? Opus 4.6 takes the crown.

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What's your experience with these models? Drop a comment or clap if this breakdown helped you decide which model to try next!