GPT-6 Astra vs GPT-5.6 Sol: is the 6-series flagship worth 2.5x the price?
GPT-5.6 Sol stays the right default. It's 2.5x cheaper on input, output, and cached input with the same discounts and the same context. Pay the Astra premium only on reasoning Sol demonstrably can't finish.
The new flagship versus the old flagship within OpenAI's lineup - a 2.5x price gap.
GPT-6 Astra is OpenAI's newest flagship reasoning model, replacing GPT-5.6 Sol at the top of the stack. It costs 2.5x Sol's rate on both input and output. Both share the same 90% cache discount, 50% batch discount, and 1.05M context window, so the entire question is whether Astra's newer reasoning depth earns its premium.
By TechCompare · Updated
Cost Comparison
Based on 100,000 input tokens (50% cached), 5,000 output tokens, and 100 requests.Prices are fetched live from OpenRouter and may include temporary promotional discounts not accounted for in our article and comparison figures.
Side-by-side specs
| Spec | GPT-6 Astra | GPT-5.6 Sol |
|---|---|---|
| Input Cost (per M) | $10.00 | $4.00 (better on this spec) |
| Output Cost (per M) | $50.00 | $20.00 (better on this spec) |
| Cached Input (per M) | $1.00 | $0.40 (better on this spec) |
| Batch Discount | 50% | 50% |
| Context Window | 1.05M | 1.05M |
How they differ
GPT-6 Astra is priced at $10.00 per million input tokens and $50.00 per million output tokens, with a 90% caching discount ($1.00 per million) and a 50% batch discount ($5/$25), across a 1.05M context window. GPT-5.6 Sol is priced at $4.00 per million input tokens and $20.00 per million output tokens, also with a 90% caching discount ($0.40 per million) and a 50% batch discount ($2/$10), on the same 1.05M context. For a representative 100K input + 10K output request, Astra costs $1.50 versus Sol's $0.60 - a 2.5x per-call gap. Discounts scale proportionally, so they never close the ratio.
Verdict
Sol wins every priced row: $4.00/M input versus $10.00, $20.00/M output versus $50.00, and $0.40/M cached versus $1.00, while batch (50%) and context (1.05M) tie. The per-call gap is the real story - a 100K input + 10K output request costs $0.60 on Sol against $1.50 on Astra, and at a million calls that's roughly a $900K difference. Because both apply identical 90% cache and 50% batch discounts, the 2.5x ratio holds in every mode; there's no discount lever that makes Astra relatively cheaper. Astra earns its premium only on frontier reasoning that Sol demonstrably stalls on.
Which should you pick?
Choose GPT-6 Astra
Frontier-tier reasoning that Sol demonstrably can't complete: hardest math, deep multi-step agentic planning, novel code synthesis. Treat Astra as the top of a cascade, escalating only the calls Sol retries.
Choose GPT-5.6 Sol
Default production: chat, RAG, content generation, classification, and most reasoning. Sol's $4/$20 with the same 90% cache and 50% batch discounts makes it the right flagship default at a fraction of the price.