Claude Sonnet 4.5 vs InternLM 2.5 20B

Compare Claude Sonnet 4.5 and InternLM 2.5 20B: 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 Claude Sonnet 4.5 InternLM 2.5 20B
CategoryFrontierOpen Source
Parameters~600B20B
Context Window200K256K
Input Price$0.03/1M tokens$0.02/1M tokens
Output Price$0.15/1M tokens$0.04/1M tokens
Latency~350ms~180ms

Choose Claude Sonnet 4.5 when:

  • ✓ Code generation
  • ✓ Structured output
  • ✓ Automation
Key Strengths:

Strong coding, Better instruction following, Reliable

Choose InternLM 2.5 20B when:

  • ✓ Long context tasks
  • ✓ Research
  • ✓ Multilingual
Key Strengths:

256K context, Strong reasoning, Good multilingual

Verdict: Claude Sonnet 4.5 vs InternLM 2.5 20B

For cost efficiency, InternLM 2.5 20B wins at $0.02/1M input tokens. For speed, InternLM 2.5 20B is faster at ~180ms. Claude Sonnet 4.5 excels at Code generation while InternLM 2.5 20B is better for Long context tasks. Both are available on XALEN through a single API — try them in the Playground to see which fits your workload.

Detailed Analysis

Pricing Comparison

Claude Sonnet 4.5 costs $0.03/1M input tokens and $0.15/1M output tokens. InternLM 2.5 20B costs $0.02 input and $0.04 output. InternLM 2.5 20B is 1.5x cheaper on input tokens. XALEN offers batch processing at 50% discount on both models.

Performance & Context

Claude Sonnet 4.5 has a 200K context window with ~350ms latency. InternLM 2.5 20B offers 256K context at ~180ms. InternLM 2.5 20B has the larger context window.

Best For

Claude Sonnet 4.5 (Frontier) is optimized for: Code generation, Structured output, Automation. InternLM 2.5 20B (Open Source) works best for: Long context tasks, Research, Multilingual.

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 Claude Sonnet 4.5
response_a = client.chat.completions.create(
    model="claude-sonnet-4-5",
    messages=[{"role": "user", "content": "Your question here"}]
)

# Use InternLM 2.5 20B
response_b = client.chat.completions.create(
    model="internlm-2-5-20b",
    messages=[{"role": "user", "content": "Your question here"}]
)

Start Building with XALEN

200+ AI models. One API. Pay-as-you-go.

Get API Key Try in Playground

Frequently Asked Questions

Which is better, Claude Sonnet 4.5 or InternLM 2.5 20B?

Claude Sonnet 4.5 (Frontier, ~600B) offers Strong coding. InternLM 2.5 20B (Open Source, 20B) offers 256K context. Choose Claude Sonnet 4.5 for Code generation or InternLM 2.5 20B for Long context tasks.

How much does Claude Sonnet 4.5 cost vs InternLM 2.5 20B?

Claude Sonnet 4.5: $0.03/1M input, $0.15/1M output. InternLM 2.5 20B: $0.02/1M input, $0.04/1M 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 Claude Sonnet 4.5 and InternLM 2.5 20B 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.