The short answer: Terra on API price, Sonnet on app access
Choose GPT-6.1 Terra if API cost per token is the deciding factor, at $1 input and $5 output per million tokens against Sonnet's $2 and $10, or if you already use ChatGPT Work or Codex. Choose Claude Sonnet 5.5 if you want the model in a free chat app, since Claude Free includes it, or you already build on Anthropic's API. Artificial Analysis scored both 42% on FrontierCode 2.0.
Scope and evidence
Task: everyday coding, document and agent work for an individual or small team, through each vendor's API and apps. Prices are in US dollars from OpenAI's Terra page, Anthropic's Sonnet 5.5 overview and Claude pricing page, with FrontierCode 2.0 results from Artificial Analysis, checked on October 28, 2026.
We ran no prompts on either model for this page, and Artificial Analysis did not publish an overall Intelligence Index score for Terra in its v5 announcement.
Compare the same criteria
Every line puts OpenAI's mid-priced model next to Anthropic's, then states what follows from it.
- API price per million tokens. Terra: $1 input and $5 output, with cached input at $0.05. Sonnet 5.5: $2 input, $0.10 cache read, $10 output. What this means: Terra is half the list price.
- Reasoning control. Terra: effort none to max, default medium. Sonnet 5.5: adaptive thinking with default effort high, and a between_tools setting that turns off up-front thinking at high effort or below. What this means: both let you cut reasoning for simple calls.
- Context and output. Terra: 1.05M tokens, 128K output. Sonnet 5.5: 1M tokens, 128K output, up to 300K output on the Batch API in beta. What this means: Sonnet allows longer batch outputs.
- Knowledge cutoff. Terra: June 1, 2026. Sonnet 5.5: June 2026. What this means: about the same.
- Independent coding result. FrontierCode 2.0 at max effort: Terra 42%, Sonnet 5.5 42%, per Artificial Analysis. What this means: no gap on that benchmark.
- App access. Terra: ChatGPT Work and Codex on Plus, Pro, Enterprise and Edu, not regular chats. Sonnet 5.5: Claude Free, Pro and Max. What this means: only Sonnet is free in a chat app.
Which fits your real work?
A startup processing thousands of support screenshots a day through an API. Terra fits on list price and OpenAI's focus on visual reasoning.
A student who wants a capable model in a free chat app. Sonnet 5.5 fits, because Claude Free includes it and Terra needs a paid ChatGPT plan.
A team already running agents on Anthropic's API that needs long batch outputs. Sonnet 5.5 fits with its 300K Batch output beta.
Cost of getting the work done
API: 2 million input and 200,000 output tokens cost $3 on Terra and $6 on Sonnet 5.5 before caching, with 50% off batch on both. Measure tokens per task, since the same job can use different amounts on each model.
Apps, per month: ChatGPT Plus at $20 includes Terra in Work and Codex. Claude Free includes Sonnet at $0, and Claude Pro is $20 billed monthly or $17 a month billed annually.
Try both on the same small task
Suggested check: give both models one screenshot-reading task and one short writing task, the two areas OpenAI highlights for Terra.
- Every toggle in the screenshot appears in the table with the right state.
- The note stays near 120 words and names exactly three settings.
- The privacy reasoning matches what each setting actually does.
- Score each model across three screenshots, not one.
Decision checklist
Use the lines that fit you. Details are in our GPT-6.1 Terra profile and our Claude Sonnet 5.5 profile.
- If API list price matters most, start with Terra.
- If you need it free in a chat app, use Sonnet 5.5 on Claude Free.
- If you already pay for ChatGPT Plus and use Codex, Terra is included there.
- If you need batch outputs above 128K tokens, Sonnet 5.5 offers 300K in beta.
- If coding quality decides it, test both: FrontierCode 2.0 shows them level.
Go to the source
Sources & further reading
Based on the official documentation below. Features and access can change; check the provider before making a decision.
Was this page useful?
Help us make our coverage more useful. This is feedback on the page, not a rating of the tool.
Go a little further