GPT-4o vs Claude Sonnet 4

GPT-4o and Claude Sonnet 4 are mid-tier frontier models priced for production use. GPT-4o costs $2.50 input / $10.00 output per million tokens with a 128K context window. Claude Sonnet 4 costs $3.00 input / $15.00 output with a 200K context window. Pick GPT-4o for creative tasks and tighter budgets; pick Sonnet 4 when you need the larger context or prefer Anthropic’s safety tuning.

Specification comparison

When to use GPT-4o

Cost-sensitive production workloads. GPT-4o is 16% cheaper on input and 33% cheaper on output. If your prompts fit in 128K tokens and cost matters more than the marginal quality difference, GPT-4o is the better pick.

Creative writing and marketing copy. GPT-4o excels at generating varied, engaging prose. User reports consistently rate it higher for blog posts, ad copy, and narrative content compared to Sonnet 4’s more literal, technical output.

Faster iteration during development. OpenAI’s API tends to have lower latency and higher rate limits by default. If you are prototyping and need tight feedback loops, GPT-4o responds faster.

When to use Claude Sonnet 4

Long-context tasks. Sonnet 4 handles 200K tokens, 56% more than GPT-4o’s 128K. For document analysis, multi-file codebases, or research tasks requiring full-text citation tracking, Sonnet 4 works where GPT-4o would need chunking.

Safety-critical applications. Anthropic tunes Claude models for refusal on harmful requests more aggressively than OpenAI. If your use case involves user-generated prompts and you need strong safety rails, Sonnet 4 is the safer default.

Instruction-following precision. Sonnet 4 scores higher on tasks requiring exact adherence to complex, multi-step instructions (measured by internal evals and user feedback). For structured data extraction or API output generation, Sonnet 4 is more reliable.

Use both through one API

Rhodes routes to both models using the same SDK and key. Switch between them per request by changing the model parameter:

import OpenAI from 'openai';

const client = new OpenAI({
  baseURL: 'https://api.rhodes.ai/v1',
  apiKey: process.env.RHODES_KEY,
});

// GPT-4o for creative task
const creative = await client.chat.completions.create({
  model: 'openai/gpt-4o',
  messages: [{ role: 'user', content: 'Write a product tagline.' }],
});

// Claude Sonnet 4 for long-context task
const analysis = await client.chat.completions.create({
  model: 'anthropic/claude-sonnet-4',
  messages: [{ role: 'user', content: 'Summarize this 150K token document.' }],
});

No separate contracts, no separate keys, no separate balances. One prepaid account, switch models per request based on the task.

FAQ

Which one is “better”?

Neither. They have different strengths. GPT-4o is cheaper and faster for sub-128K tasks. Sonnet 4 is stronger on long-context and safety-critical work. The right choice depends on your specific use case.

Can I use both through the same API key?

Yes. Rhodes routes to both OpenAI and Anthropic through the same endpoint and key. Change the model parameter per request. Your prepaid balance covers both.

Do they support the same features?

Both support streaming, tool use (function calling), and vision. Response formats are OpenAI-compatible, so your SDK code works identically for both models.

How do I decide which to use?

Start with GPT-4o for cost. If you hit the 128K context limit or need stronger instruction-following, switch to Sonnet 4. Use fallbacks to try GPT-4o first and automatically retry with Sonnet 4 if the context is too long.

Related resources

Claude Sonnet 4 Model Page — Full specs, pricing, and code examples.

Model Fallbacks — Set backup models per request with automatic retry.

Getting Started — Make your first request through Rhodes in 5 minutes.

Pricing — Compare all model prices and calculate your costs.