# GPT-5.6 Terra vs GPT-5.5

> Markdown mirror of https://router.one/models/compare/gpt-5-6-terra-vs-gpt-5-5 for AI assistants and crawlers. Router One is a unified, OpenAI-compatible LLM API gateway.

GPT-5.6 Terra is the lower-priced of the two on Router One at base-tier rates (GPT-5.6 Terra: request input ≤ 272,000 tokens) — about 36% less on a 1M-input + 1M-output mix. GPT-5.6 Terra's lower 1M-input + 1M-output total holds only for requests of up to 272,000 input tokens; above that both come to $2.75. Both carry a 1.05M context window. Both answer on /v1/chat/completions and /v1/responses (Codex CLI). GPT-5.6 Terra counts against the Mid-tier models allowance on Pro, Max and Ultra; GPT-5.5 counts against the Premium models allowance on Pro, Max and Ultra.

GPT-5.6 Terra and GPT-5.5 compared on current per-token rates, context window, and capabilities — both callable through one OpenAI-compatible endpoint with per-request cost traces.

## GPT-5.6 Terra vs GPT-5.5: rates, context window, and capabilities

| Spec | GPT-5.6 Terra | GPT-5.5 |
| --- | --- | --- |
| Input / 1M tokens | $0.25 | $0.50 |
| Output / 1M tokens | $1.50 | $2.25 |
| Cached input / 1M tokens | $0.125 | $0.125 |
| Context window | 1.05M | 1.05M |
| Capabilities | Chat, Streaming, Tool calling, Vision | Chat, Streaming, Tool calling, Vision |
| Subscription plans | Mid-tier models — Pro, Max, Ultra | Premium models — Pro, Max, Ultra |
| Detail page | [GPT-5.6 Terra](https://router.one/models/gpt-5-6-terra) | [GPT-5.5](https://router.one/models/gpt-5-5) |

GPT-5.6 Terra: request input ≤ 272,000 tokens: Input $0.25 / 1M tokens, Output $1.50 / 1M tokens, Cache write $0.25 / 1M tokens, Cached input $0.125 / 1M tokens; request input > 272,000 tokens: Input $0.50 / 1M tokens, Output $2.25 / 1M tokens, Cache write $0.50 / 1M tokens, Cached input $0.25 / 1M tokens. The total input tokens in each request select the tier; its rates apply to the whole request, not only tokens above the threshold.

## What does 1M tokens cost on GPT-5.6 Terra vs GPT-5.5?

Base-tier rates: For a workload of 1M input plus 1M output tokens at current rates: GPT-5.6 Terra comes to $1.75, GPT-5.5 comes to $2.75 — GPT-5.6 Terra is about 36% cheaper on this mix. Real workloads skew heavily toward input tokens, so weigh the input rate by your own ratio; the cached-input row above is the posted catalog rate for that model.

## Switch between GPT-5.6 Terra and GPT-5.5 without changing code

Both models are behind the same OpenAI-compatible endpoint, so an A/B test is a one-string change — same key, same code, and every request traced with tokens, cost, and latency in the dashboard:

`compare.sh`

```bash
curl https://api.router.one/v1/chat/completions \
  -H "Authorization: Bearer sk-your-router-one-key" \
  -H "Content-Type: application/json" \
  -d '{"model": "openai/gpt-5.6-terra", "messages": [{"role": "user", "content": "Hello"}]}'

# Same request, other model — change one string:
#   "model": "openai/gpt-5.5"
```

## FAQ

### Is GPT-5.6 Terra cheaper than GPT-5.5?

Compared at base-tier rates (GPT-5.6 Terra: request input ≤ 272,000 tokens). Input: GPT-5.6 Terra $0.25 vs GPT-5.5 $0.50 / 1M tokens; GPT-5.6 Terra has the lower rate. Output: GPT-5.6 Terra $1.50 vs GPT-5.5 $2.25 / 1M tokens; GPT-5.6 Terra has the lower rate. GPT-5.6 Terra's lower 1M-input + 1M-output total holds only for requests of up to 272,000 input tokens; above that both come to $2.75. Total cost depends on the workload's input, output and cache usage. GPT-5.6 Terra: request input ≤ 272,000 tokens: Input $0.25 / 1M tokens, Output $1.50 / 1M tokens, Cache write $0.25 / 1M tokens, Cached input $0.125 / 1M tokens; request input > 272,000 tokens: Input $0.50 / 1M tokens, Output $2.25 / 1M tokens, Cache write $0.50 / 1M tokens, Cached input $0.25 / 1M tokens. The total input tokens in each request select the tier; its rates apply to the whole request, not only tokens above the threshold. Rates change; the /models page is the live source of truth.

### Is GPT-5.6 Terra or GPT-5.5 included in a Router One subscription?

GPT-5.6 Terra counts against the Mid-tier models allowance on Pro, Max and Ultra: Pro 1,200, Max 4,500 and Ultra 15,000 requests per 30-day cycle, shared by every model in that tier. GPT-5.5 counts against the Premium models allowance on Pro, Max and Ultra: Pro 300, Max 1,000 and Ultra 5,000 requests per 30-day cycle, shared by every model in that tier. Requests to GPT-5.6 Terra or GPT-5.5 above the model's long-context threshold count as more than one quota request. Requests beyond a plan's allowance bill the wallet per token.

### Can I switch between GPT-5.6 Terra and GPT-5.5 without changing code?

Yes. Both are served through the same OpenAI-compatible endpoint, so switching is changing the model string in the request — the key, base URL, and request shape stay identical.

### Where do these numbers come from?

Specs and prices on this page render from the live Router One catalog — the same data as the /models page — and refresh with it. Pricing methodology is documented on /pricing-methodology. Rates on this page were read from the live catalog on 2026-09-30 (UTC) and refresh within the hour.

## More comparisons

- [Gemini 3.8 Flash vs GPT-5.5](https://router.one/models/compare/gemini-3-8-flash-vs-gpt-5-5)
- [GPT-5.6 Terra vs Claude Sonnet 5](https://router.one/models/compare/gpt-5-6-terra-vs-claude-sonnet-5)
- [Grok 4.7 vs GPT-5.5](https://router.one/models/compare/grok-4-7-vs-gpt-5-5)
- [GPT-5.6 Sol (Azure) vs GPT-5.6 Sol](https://router.one/models/compare/azure-gpt-5-6-sol-vs-gpt-5-6-sol)

## See also

- Canonical page: https://router.one/models/compare/gpt-5-6-terra-vs-gpt-5-5
- All model comparisons: https://router.one/models/compare
- All models & prices: https://router.one/models (markdown: https://router.one/models.md)
- Pricing: https://router.one/pricing
- GPT API access: https://router.one/cheap-gpt-api
- Cost calculator: https://router.one/llm-cost-calculator
- Pricing methodology: https://router.one/pricing-methodology