Llama 3.1 405B vs o3 Pro

Compare Llama 3.1 405B and o3 Pro: pricing, performance, context window, latency, and best use cases. Side-by-side comparison on XALEN.

Updated 2026-05-21 · By Abhishek Raj · Our methodology

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Feature Llama 3.1 405B o3 Pro
CategoryOpen SourceReasoning
Parameters405B~1T
Context Window128K200K
Input Price$0.08/1M tokens$0.15/1M tokens
Output Price$0.14/1M tokens$0.60/1M tokens
Latency~600ms~5000ms

Choose Llama 3.1 405B when:

  • ✓ Premium tasks
  • ✓ Research
  • ✓ Fine-tuning base
Key Strengths:

Largest open model, Highest open-source quality

Choose o3 Pro when:

  • ✓ Research-grade reasoning
  • ✓ Mathematical proofs
  • ✓ Hardest problems
Key Strengths:

Deepest reasoning, Best for hard problems, Highest accuracy

Verdict: Llama 3.1 405B vs o3 Pro

For cost efficiency, Llama 3.1 405B wins at $0.08/1M input tokens. For speed, o3 Pro is faster at ~5000ms. Llama 3.1 405B excels at Premium tasks while o3 Pro is better for Research-grade reasoning. Both are available on XALEN through a single API — try them in the Playground to see which fits your workload.

Detailed Analysis

Pricing Comparison

Llama 3.1 405B costs $0.08/1M input tokens and $0.14/1M output tokens. o3 Pro costs $0.15 input and $0.60 output. Llama 3.1 405B is 1.9x cheaper on input tokens. XALEN offers batch processing at 50% discount on both models.

Performance & Context

Llama 3.1 405B has a 128K context window with ~600ms latency. o3 Pro offers 200K context at ~5000ms. o3 Pro has the larger context window.

Best For

Llama 3.1 405B (Open Source) is optimized for: Premium tasks, Research, Fine-tuning base. o3 Pro (Reasoning) works best for: Research-grade reasoning, Mathematical proofs, Hardest problems.

Try Both on XALEN

Both models are available through XALEN's OpenAI-compatible API. Switch between them by changing the model parameter:

from xalen import XALEN

client = XALEN(api_key="xln_test_YOUR_KEY")

# Use Llama 3.1 405B
response_a = client.chat.completions.create(
    model="llama-3-1-405b",
    messages=[{"role": "user", "content": "Your question here"}]
)

# Use o3 Pro
response_b = client.chat.completions.create(
    model="o3-pro",
    messages=[{"role": "user", "content": "Your question here"}]
)

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Frequently Asked Questions

Which is better, Llama 3.1 405B or o3 Pro?

Llama 3.1 405B (Open Source, 405B) offers Largest open model. o3 Pro (Reasoning, ~1T) offers Deepest reasoning. Choose Llama 3.1 405B for Premium tasks or o3 Pro for Research-grade reasoning.

How much does Llama 3.1 405B cost vs o3 Pro?

Llama 3.1 405B: $0.08/1M input, $0.14/1M output. o3 Pro: $0.15/1M input, $0.60/1M output. Both available on XALEN with batch processing at 50% discount.

Can I use both models on XALEN?

Yes. XALEN provides 200+ models through a single OpenAI-compatible API. Switch between Llama 3.1 405B and o3 Pro by changing the model parameter. No code changes needed.

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Last updated: 2026-05-21. Pricing and specifications may change. Check pricing page for latest rates.