Which is cheaper, Claude Opus 5.5 and GPT-6.1 Terra?

GPT-6.1 Terra has the lowest input price. Per 1M input tokens: Claude Opus 5.5 from $4.00 and GPT-6.1 Terra from $1.00.

Which has the larger context window, Claude Opus 5.5 and GPT-6.1 Terra?

GPT-6.1 Terra has the largest context window: Claude Opus 5.5 1,000,000 tokens and GPT-6.1 Terra 1,050,000 tokens.

Which is smarter, Claude Opus 5.5 and GPT-6.1 Terra?

Claude Opus 5.5 scores highest on the Artificial Analysis Intelligence Index: Claude Opus 5.5 58.4 and GPT-6.1 Terra 51.0.

Can I switch between Claude Opus 5.5 and GPT-6.1 Terra without changing my code?

Yes. All of them are served through FastRouter's OpenAI-compatible API, so switching is a change of the model parameter (anthropic/claude-opus-5.5, openai/gpt-6.1-terra).

Claude Opus 5.5 vs GPT-6.1 Terra

Side-by-side pricing per provider, context window, benchmark scores and speed, all on one OpenAI-compatible API.

Estimate monthly cost for these models

Claude Opus 5.5 Anthropicanthropic/claude-opus-5.5

GPT-6.1 Terra OpenAIopenai/gpt-6.1-terra

Creator

Anthropic

OpenAI

Released

Sep 22, 2026

Oct 26, 2026

Context window

1.05M

Max output

128K

Input / 1MLowest provider price

$4.00

$1.00

Output / 1MLowest provider price

$20.00

$5.00

Providers

IntelligenceArtificial Analysis index

58.4

51.0

Accepts

Text, Image, Files

Produces

Text

Tool calling

Yes

Structured output

Yes

Reasoning

Yes

Claude Opus 5.5 vs GPT-6.1 Terra: summary

Claude Opus 5.5 and GPT-6.1 Terra are both available through FastRouter's OpenAI-compatible API, so switching between them is a change of model id, not a new integration.

Claude Opus 5.5, from Anthropic, has a 1,000,000-token context window, costs from $4.00/1M input and $20.00/1M output tokens across 3 providers and scores 58.4 on the Artificial Analysis Intelligence Index.

GPT-6.1 Terra, from OpenAI, has a 1,050,000-token context window, costs $1.00/1M input and $5.00/1M output tokens and scores 51.0 on the Artificial Analysis Intelligence Index.

GPT-6.1 Terra is the cheapest on input, 4× cheaper than the next model, GPT-6.1 Terra has the largest context window and Claude Opus 5.5 scores highest for intelligence.

Switch with one line

client = OpenAI(base_url="https://api.fastrouter.ai/api/v1", api_key="<FASTROUTER_API_KEY>") client.chat.completions.create(model="anthropic/claude-opus-5.5", messages=[...]) # or client.chat.completions.create(model="openai/gpt-6.1-terra", messages=[...])

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Benchmark scores sourced from ArtificialAnalysis