GPT-5 vs. GPT-5.6 Terra: API Cost Comparison
On this API, GPT-5 costs $0.4375 / $3.5 per 1M tokens (in/out) and GPT-5.6 Terra costs $0.7 / $4.2. GPT-5 is the cheaper option, and both run on the same key — switching is a one-line model parameter change.
Per-token pricing
| GPT-5 | GPT-5.6 Terra | |
|---|---|---|
| Vendor | OpenAI | OpenAI |
| Input · per 1M tokens · Official list | $1.25 | $2 |
| Input · per 1M tokens · Your price | $0.4375 | $0.7 |
| Output · per 1M tokens · Official list | $10 | $12 |
| Output · per 1M tokens · Your price | $3.5 | $4.2 |
| Discount vs. list | -65% | -65% |
| Context window | 400K tokens | 400K tokens |
| Max output tokens | 128K tokens | 128K tokens |
All prices in USD per 1M tokens.
What a real workload costs
Same request stream priced on both models — 10M input + 2M output tokens per month, a typical coding-agent load:
GPT-5
- At official list
- $32.5 per month
- On this API
- $11.38 per month
GPT-5.6 Terra
- At official list
- $44 per month
- On this API
- $15.4 per month
Switching between them
Both models answer on the same endpoint. Keep your base URL and key; change only the model parameter to reroute a request:
curl https://kktt.net/v1/chat/completions \
-H "Authorization: Bearer $API_KEY" \
-d '{"model": "gpt-5", "messages": [...]}'curl https://kktt.net/v1/chat/completions \
-H "Authorization: Bearer $API_KEY" \
-d '{"model": "gpt-5.6-terra", "messages": [...]}'FAQ
Which is cheaper, GPT-5 or GPT-5.6 Terra?
On this API, GPT-5 is cheaper: $0.4375 in / $3.5 out per 1M tokens, versus $0.7 in / $4.2 out for GPT-5.6 Terra.
Can I use GPT-5 and GPT-5.6 Terra with the same API key?
Yes. Both are callable with one key on the same base URL — switching between them is a one-line change of the model parameter, which makes A/B testing or fallback routing trivial.
Do GPT-5 and GPT-5.6 Terra differ in context window?
GPT-5 supports 400K of context with 128K max output; GPT-5.6 Terra supports 400K with 128K max output.