GPT-5.5 Pro vs Llama 3.1 405B
How do these models stack up? Below is an expert side-by-side comparison of specifications, context window capacity, live pricing per million tokens, and standardized benchmark scores for GPT-5.5 Pro and Llama 3.1 405B.
GPT-5.5 Pro
GPT-5.5 Pro is OpenAI’s high-capability model optimized for deep reasoning and accuracy on complex, high-stakes workloads. It features a 1M+ token context window (922K input, 128K output) with support for...
Llama 3.1 405B
Llama 3.1 405B is Meta's largest open-weight language model and one of the most capable openly available models in the world. With 405 billion parameters, it achieves performance competitive with GPT-4 and Claude Opus across benchmarks spanning general knowledge, mathematics, coding, and multilingual tasks. Llama 3.1 405B is released under Meta's custom commercial license, supporting broad use cases including deployment via major cloud providers (AWS, GCP, Azure) and self-hosted inference with multi-GPU configurations.
Technical Specifications
| Specification | GPT-5.5 Pro | Llama 3.1 405B |
|---|---|---|
| Provider | OpenAI | Meta |
| Context Window | 1,050,000 tokens | 131,072 tokens |
| Agent Suitability | 98/100 | 90/100 |
| Time to First Token (TTFT) | 450 ms | 550 ms |
| Deployment Model | managed api | self hostable |
| Production Stability | beta | stable |
| API Available | Yes | Yes |
| Released Date | 2026-04-24 | 2024-07-23 |
API Pricing Comparison
Input Price per Million Tokens
GPT-5.5 Pro
$30.00
Llama 3.1 405B
$0.80
Output Price per Million Tokens
GPT-5.5 Pro
$180.00
Llama 3.1 405B
$0.80
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Benchmark Performance Metrics
Scores show the raw performance percentages verified across key evaluation suites. Higher bars indicate superior accuracy and capability in that domain.
GPT-5.5 Pro Quirks & Gotchas
- ▸Best-in-class instruction following for complex agentic chains
- ▸Premium pricing — use GPT-5 for cost-sensitive workloads
Llama 3.1 405B Quirks & Gotchas
- ▸Massive model — requires 8× A100 80GB for FP16 inference
- ▸Available via Together AI, Fireworks, and Bedrock as managed API