Compare / Models
Claude Sonnet 4.5 vs GPT-5.5
Price, context window and capabilities side by side — read from the same catalog that meters your calls, not from a press release.
Claude Sonnet 4.5 is 1.7x cheaper on input. Claude Sonnet 4.5 is 2.0x cheaper on output. GPT-5.5 holds 256K tokens against 200K.
At a glance
Side by side
Anthropic
Frontier-quality text and reasoning through one OpenAI-compatible endpoint.
Specifications
Every difference we can measure
| Claude Sonnet 4.5 | GPT-5.5 | |
|---|---|---|
| Input price | $3/M | $5/M |
| Output price | $15/M | $30/M |
| Context window | 200K tokens | 256K tokens |
| Vision | Yes | Yes |
| Tool calling | Yes | Yes |
| Prompt caching | Yes | No |
A row appears only when we hold the fact for both models. Anything the provider has not published is left out rather than guessed, so an empty row is missing data and never a zero.
Verdict
Which to pick
GPT-5.5 wins on raw reasoning benchmarks and cheap input tokens; Sonnet 4.5 wins on tool-calling reliability and sustained code-edit quality. Most teams route the agent loop to Sonnet and heavy one-shot analysis to GPT-5.5, with one key, that split is a config line, not a second vendor contract.
Keep looking
Related comparisons
FAQ
Frequently asked questions
What is the difference between Claude Sonnet 4.5 and GPT-5.5?
Claude Sonnet 4.5 is 1.7x cheaper on input. Claude Sonnet 4.5 is 2.0x cheaper on output. GPT-5.5 holds 256K tokens against 200K. Only Claude Sonnet 4.5 declares prompt caching. Both run on the same endpoint and the same key here, so trying each is a one-line change to the model id.
Which is cheaper, Claude Sonnet 4.5 or GPT-5.5?
Claude Sonnet 4.5 is, on input tokens. Output usually dominates the bill on generative work, so check the output row above against your own ratio of prompt to completion before deciding.
Can I switch between Claude Sonnet 4.5 and GPT-5.5 without changing my code?
Yes. Both are OpenAI-compatible through one CompanyFabric key, so switching is the model string and nothing else — no second SDK, no second contract, one prepaid balance across both.
Do I have to choose?
No. Send companyfabric/auto and we route each request to the cheapest model that can serve it, which is how most people use both without deciding in advance.
One key. Every model. Exact prices.
Run Claude Sonnet 4.5 and GPT-5.5 on the same key and compare them on your own prompts. Free starter credits included, no subscription required.