GPT-5.6 Terra Pro is $8 cheaper per 1M input tokens (80% lower; 5x difference).
API cost decision in 10 seconds
NewGPT-6 Astra vs GPT-5.6 Terra Pro
Pick GPT-5.6 Terra Pro when budget is the priority.
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Data confirmed:
Prices normalized to USD per 1M tokens
Sample workload: 1M input + 500K output
Budget verdict
Pick GPT-5.6 Terra Pro when budget is the priority.
On the standard 1M input plus 500K output workload, GPT-5.6 Terra Pro is estimated at $8 vs $35 for GPT-6 Astra, saving $27 (77.1% lower).
Cost-first pickGPT-5.6 Terra Pro
Context-first pickBoth models
Sample savings$2777.1%
10x traffic gap$270
The reported context window is tied, so cost and provider fit carry more weight. At 10x that traffic, the same price gap is about $270. Use the calculator below to replace the sample workload with your own token volume.
Cost sensitivity
Workload Sensitivity
GPT-5.6 Terra Pro stays cheaper across input-heavy, balanced, and output-heavy sample workloads.
| Workload shape | Token mix | Better pick | GPT-6 Astra | GPT-5.6 Terra Pro |
|---|---|---|---|---|
| Input-heavy / RAG | 5M input + 500K output | GPT-5.6 Terra Pro | $75 | $16 |
| Balanced workload | 1M input + 1M output | GPT-5.6 Terra Pro | $60 | $14 |
| Output-heavy chatbot | 1M input + 5M output | GPT-5.6 Terra Pro | $260 | $62 |
GPT-5.6 Terra Pro is $38 cheaper per 1M output tokens (76% lower; 4.17x difference).
Both models report the same context window at 1.05M tokens.
GPT-5.6 Terra Pro is $27 cheaper on the standard workload (77.1% lower).
Estimate your workload cost
Your Workload Cost
This estimate uses normalized public API pricing per 1M tokens. It is a planning aid, not a billing quote. Verify provider pricing, limits, and terms before production use.
Quick Decision
GPT-5.6 Terra Pro has the lower input price; GPT-5.6 Terra Pro has the lower output price; both models report the same context window. For the 1M input plus 500K output sample, GPT-5.6 Terra Pro is cheaper for the standard workload.
For a 1M input token plus 500K output token workload, the estimated API cost is $35 for GPT-6 Astra and $8 for GPT-5.6 Terra Pro.
Choose GPT-6 Astra when its provider, model quality, latency, or availability is more important than the numeric price/context winner.
Choose GPT-5.6 Terra Pro when you care most about lower input-token price, and lower output-token price.
- On the standard 1M input plus 500K output workload, GPT-5.6 Terra Pro is estimated at $8 vs $35 for GPT-6 Astra, saving $27 (77.1% lower).
- GPT-5.6 Terra Pro is $27 cheaper on the standard workload (77.1% lower).
- GPT-5.6 Terra Pro is $8 cheaper per 1M input tokens (80% lower; 5x difference).
- GPT-5.6 Terra Pro is $38 cheaper per 1M output tokens (76% lower; 4.17x difference).
- Both models report the same context window at 1.05M tokens.
| Feature | NewGPT-6 Astra (OpenAI) | GPT-5.6 Terra Pro (OpenAI) |
|---|---|---|
| Input Price prompt tokens per 1M | $10 | $2 |
| Completion Price per 1M tokens | $50 | $12 |
| Sample Workload Cost 1M input + 500K output | $35 | $8 |
| Context Window | 1.05M | 1.05M |
| Release Date |
Use-Case Decision Matrix
| Use case | Better pick | Why |
|---|---|---|
| Budget-constrained production | GPT-5.6 Terra Pro | On the standard 1M input plus 500K output workload, GPT-5.6 Terra Pro is estimated at $8 vs $35 for GPT-6 Astra, saving $27 (77.1% lower). |
| High-volume input processing | GPT-5.6 Terra Pro | Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill. |
| Long responses and chatbots | GPT-5.6 Terra Pro | Lower output-token price matters most when assistants generate many completion tokens. |
| RAG or long-document work | Tie | A larger context window leaves more room for retrieved passages, conversation history, or source files. |
Related Alternatives
- gpt-oss-120b (free) can replace GPT-6 Astra when lower sample workload cost matters most: $0.
- gpt-oss-20b (free) can replace GPT-6 Astra when lower sample workload cost matters most: $0.
- gpt-oss-20b can replace GPT-6 Astra when lower sample workload cost matters most: $0.1.
- gpt-oss-120b can replace GPT-6 Astra when lower sample workload cost matters most: $0.12.
- Grok 4.20 Multi-Agent offers 2M context with $2.5 sample workload cost.
- Grok 4.20 offers 2M context with $2.5 sample workload cost.
- GLM 5.3 Flash offers 1.31M context with $0.2 sample workload cost.
- DeepSeek V4 Flash 0731 offers 1.31M context with $0.15 sample workload cost.
- GLM 5.3 Flash · Z.ai · #1
- GPT-5.6 Luna · OpenAI · #2
- DeepSeek V4 Flash 0731 · DeepSeek · #3
- Hy4 preview · Tencent · #4
Cheaper alternatives
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Review all tracked OpenAI models before deciding whether this matchup is the right shortlist.
Open OpenAI modelsGPT-6 Astra is OpenAI's flagship model for demanding end-to-end work. It is suited for advanced analysis, software engineering, deep research, scientific work, and document creation, with particular strengths in long-horizon...
GPT-5.6 Terra Pro is the same underlying model as [GPT-5.6 Terra](https://openrouter.ai/openai/gpt-5.6-terra), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. Learn more in OpenAI's docs: https://developers.openai.com/api/docs/guides/reasoning#reasoning-mode