Choose Anthropic: Claude Sonnet 5.5 if…
No advantage on the data we track — pick it for provider preference or output quality on your own prompts.
Anthropic: Claude Sonnet 5.5 vs OpenAI: GPT-6.1 Terra
OpenAI: GPT-6.1 Terra comes out ahead on the data we track: 2 advantages and none for Anthropic: Claude Sonnet 5.5.
Key numbers
| Spec | Anthropic: Claude Sonnet 5.5 | OpenAI: GPT-6.1 Terra |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Input price (per 1M tokens) | $2.00 | $1.00 |
| Output price (per 1M tokens) | $10.00 | $5.00 |
| Blended price (3:1 input/output) | $4.00 | $2.00 |
| Cheaper than … of all models we track | 15% | 25% |
| Context window | 1M tokens (~1,500 pages) | 1.1M tokens (~1,575 pages) |
| Larger context than … of all models | 68% | 92% |
| Max output per response | 128K tokens (~96,000 words) | 128K tokens (~96,000 words) |
| Input types | text, image, file | file, image, text |
| Output types | text | text |
| Free variant | No | No |
| Listed since | 2026-09-28 | 2026-10-26 |
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What it costs for real workloads
Monthly cost at list price for five common workloads. Token counts per unit are stated so you can scale them to your own traffic. A workload that does not fit a model's context window is marked rather than priced.
| Workload (per month) | Anthropic: Claude Sonnet 5.5 | OpenAI: GPT-6.1 Terra | Difference |
|---|---|---|---|
| Customer-support chatbot 50,000 conversations — each a 6-turn conversation (1,500 in / 400 out tokens) | $350 | $175 | OpenAI: GPT-6.1 Terra saves $175 |
| RAG search over documents 20,000 questions — each a question answered from ~8 retrieved passages (6,000 in / 500 out tokens) | $340 | $170 | OpenAI: GPT-6.1 Terra saves $170 |
| Coding / tool-using agent 2,000 tasks — each a multi-step task with tool calls and file context (60,000 in / 6,000 out tokens) | $360 | $180 | OpenAI: GPT-6.1 Terra saves $180 |
| Batch summarisation 10,000 documents — each a 6,000-word report summarised to a page (8,000 in / 600 out tokens) | $220 | $110 | OpenAI: GPT-6.1 Terra saves $110 |
| Long-document analysis 500 documents — each a 150-page contract or codebase read in one pass (100,000 in / 2,000 out tokens) | $110 | $55.00 | OpenAI: GPT-6.1 Terra saves $55.00 |
Capabilities side by side
| Capability | Anthropic: Claude Sonnet 5.5 | OpenAI: GPT-6.1 Terra | What it lets you do |
|---|---|---|---|
| Tool / function calling | ✓ Yes | ✓ Yes | call your APIs and run agent loops |
| Structured output (JSON schema) | ✓ Yes | ✓ Yes | return JSON that validates against your schema |
| Reasoning / thinking mode | ✓ Yes | ✓ Yes | spend extra tokens thinking before answering hard problems |
| Image input | ✓ Yes | ✓ Yes | read screenshots, charts and scanned pages |
| Audio input | — | — | take speech or audio directly |
| File / PDF input | ✓ Yes | ✓ Yes | accept documents without your own parsing step |
| Image output | — | — | generate images, not just text |
| Built-in web search | ✓ Yes | ✓ Yes | answer from live web results |
| Seed (reproducible sampling) | — | ✓ Yes | repeat a generation for tests and evals |
| Log-probabilities | — | — | read token confidence for classification and scoring |
From each model's published parameters and input/output types. “—” means not advertised, not proven absent.
Price history
- Anthropic: Claude Sonnet 5.5: price unchanged since we started tracking it on 2026-09-29.
- OpenAI: GPT-6.1 Terra: price unchanged since we started tracking it on 2026-10-27.
Which should you choose?
Choose OpenAI: GPT-6.1 Terra if…
- cost matters at scale — it is 50% cheaper on a typical 3:1 input/output mix ($175 vs $350 a month for 50,000 support chats)
- you need seed (reproducible sampling) — to repeat a generation for tests and evals; Anthropic: Claude Sonnet 5.5 does not advertise it
Frequently asked questions
Is Anthropic: Claude Sonnet 5.5 better than OpenAI: GPT-6.1 Terra?
OpenAI: GPT-6.1 Terra comes out ahead on the data we track: 2 advantages and none for Anthropic: Claude Sonnet 5.5.
Which is cheaper, Anthropic: Claude Sonnet 5.5 or OpenAI: GPT-6.1 Terra?
OpenAI: GPT-6.1 Terra is cheaper: $2.00 vs $4.00 per 1M tokens at a typical 3:1 input/output mix, 50% less. For 50,000 support conversations a month that is $175 against $350.
How much do Anthropic: Claude Sonnet 5.5 and OpenAI: GPT-6.1 Terra cost per million tokens?
Anthropic: Claude Sonnet 5.5 costs $2.00 per 1M input tokens and $10.00 per 1M output tokens; OpenAI: GPT-6.1 Terra costs $1.00 input and $5.00 output. Output tokens are billed separately, so long answers shift the gap.
Which has the bigger context window, Anthropic: Claude Sonnet 5.5 or OpenAI: GPT-6.1 Terra?
OpenAI: GPT-6.1 Terra: 1.1M tokens, about 1,575 pages, against 1M (about 1,500 pages) for Anthropic: Claude Sonnet 5.5.
Do Anthropic: Claude Sonnet 5.5 and OpenAI: GPT-6.1 Terra support function calling and JSON output?
Tool calling — Anthropic: Claude Sonnet 5.5: yes, OpenAI: GPT-6.1 Terra: yes. JSON-schema structured output — Anthropic: Claude Sonnet 5.5: yes, OpenAI: GPT-6.1 Terra: yes.
Can Anthropic: Claude Sonnet 5.5 or OpenAI: GPT-6.1 Terra read images?
Yes, both accept image input.
Is Anthropic: Claude Sonnet 5.5 or OpenAI: GPT-6.1 Terra free to use?
No free variant is listed for either; both are pay-per-token.
What is the maximum output length of Anthropic: Claude Sonnet 5.5 and OpenAI: GPT-6.1 Terra?
Anthropic: Claude Sonnet 5.5 can write up to 128K tokens (about 96,000 words) per response; OpenAI: GPT-6.1 Terra up to 128K (about 96,000 words).
When were Anthropic: Claude Sonnet 5.5 and OpenAI: GPT-6.1 Terra released?
Anthropic: Claude Sonnet 5.5 was listed on 2026-09-28; OpenAI: GPT-6.1 Terra on 2026-10-26.
About the two models
Anthropic: Claude Sonnet 5.5
Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, succeeding Claude Sonnet 5 as a direct upgrade. It is especially strong at building features, fixing bugs, and producing...
Full Anthropic: Claude Sonnet 5.5 specs →OpenAI: GPT-6.1 Terra
GPT-6.1 Terra is the mid-tier model in OpenAI's GPT-6.1 series, priced below GPT-6.1 Sol. It is suited for everyday agentic, coding, and writing work, is particularly strong at understanding screenshots...
Full OpenAI: GPT-6.1 Terra specs →