GPT-5.6 Sol vs GPT-6 Astra: what the API premium buys
GPT-5.6 Sol is the standard Chat model on ChatGPT Plus; GPT-6 Astra is the one OpenAI calls "the most intelligent and aligned model in the world". Here is what the independent numbers say the upgrade buys, and what it costs in price, speed and tools.
The usual choice
Pick one. Pay one subscription. Live inside one vendor's models.
- GPT-5.6 Sol with tool calls
- GPT-6 Astra for chat from Pro, without tools
- Plus 54+ models, one login
Per Artificial Analysis, GPT-6 Astra scores 53 to GPT-5.6 Sol’s 47 on Intelligence Index v4.3, hallucinates far less (51% against 92%) and adds 7 Coding Agent Index points for about 15% more per task. OpenAI lists Astra at $10/$50 per 1M tokens against Sol’s standard $5/$30. Sol answers sooner at max effort and takes tools on TulexAI; Astra does not.
GPT-5.6 Sol vs GPT-6 Astra vs TulexAI
| GPT-5.6 Sol | GPT-6 Astra | TulexAI | |
|---|---|---|---|
| API list price per 1M tokens (input / output) | $5 / $30 ($4 / $20 promotional, at least through Nov 21, 2026) | $10 / $50 | Astra is 25 PT per 750 tokens of prompt plus reply |
| Intelligence Index v4.3 (Artificial Analysis, max effort) | 47, #14 of 200 | 53, #3 of 200 | Astra runs at OpenAI’s default effort |
| Hallucination rate at max effort (lower is better) | 92% | 51% | Both in one chat to cross-check answers |
| Coding Agent Index (Artificial Analysis) | 55 | 62, at ~15% more cost per task | Sol keeps tool calls for agent runs |
| Knowledge-work Elo (AA-Briefcase / GDPval-AA v2) | Baseline | ~90 above Sol / ~45 below Sol | Pick the model per task |
| Output speed and time to first token at max effort | 58.8 tok/s, 131s | 58.1 tok/s, 334s | Not measured on TulexAI |
| Tool use and function calling | Supported on TulexAI | Responses API only, not Chat Completions | Sol takes tools; Astra tool requests are refused |
| ChatGPT access | Standard Chat model on Plus ($20/mo) | Plus: Work and Codex only; Chat on Pro as GPT-6 Pro | Both in one chat; Astra from Pro ($23/mo) |
Which should you pick?
Stay on GPT-5.6 Sol if your work leans on tools or function calls, if you want the first token sooner (Artificial Analysis measured 131 seconds at max effort against Astra’s 334), or if the API bill decides it: Sol lists at a standard $5/$30 per 1M tokens, $4/$20 while its promotion lasts, against Astra’s $10/$50. Move to GPT-6 Astra when a wrong answer is expensive: Artificial Analysis put its hallucination rate at 51% against Sol’s 92% and scored it six points higher on Intelligence Index v4.3 and seven on the Coding Agent Index for about 15% more per task, a far smaller gap than the list prices suggest. It is not a clean sweep, since Sol still scored about 45 Elo higher on GDPval-AA v2. Those runs used max effort and TulexAI serves Astra at OpenAI’s default, so read them as measured, not promised. On TulexAI both sit in the same chat, Astra from the $23 Pro plan at 25 PT per 750 tokens, reasoning included, so the practical move is to keep Sol for agent work and send fact-critical drafts to Astra.
Why choose at all? TulexAI includes both
54+ models in one subscription - here are the ones that cover what GPT-5.6 Sol and GPT-6 Astra each do best.
Text & Chat
- OpenAI GPT-6 AstraPremium
- GPT-5.6 SolPremium
- Claude Fable 5.1Premium
Frequently asked questions
On most of what Artificial Analysis measured, yes: 53 against 47 on Intelligence Index v4.3, 62 against 55 on the Coding Agent Index, and a 51% hallucination rate against 92%, all at max effort. Sol still leads GDPval-AA v2 by about 45 Elo and reaches its first token sooner.
On OpenAI’s API, Astra is $10 input and $50 output per 1M tokens against Sol’s standard $5 and $30: twice the input price and about 1.7 times the output price. Sol is listed at a promotional $4 and $20 at least through November 21, 2026, which makes Astra 2.5 times as much while that lasts. Astra prompts over 272K tokens bill at $20 and $75. Measured per Coding Agent Index task, Artificial Analysis found Astra only about 15% more expensive.
Only in ChatGPT Work and Codex, not regular Chat, on a limited allowance that OpenAI says Astra can use faster than GPT-5.6 Sol. In Chat it needs Pro, where it appears as GPT-6 Pro with its own message limits, or Business or Enterprise. Notebookcheck reports 50 GPT-6 Pro messages a week on the $100 Pro tier and 200 on the $200 tier.
Not on TulexAI. OpenAI supports function calling and computer use for Astra only on its Responses API, and TulexAI uses Chat Completions, so Astra refuses tool requests with a clear error. GPT-5.6 Sol supports tools on TulexAI, which makes it the model for agent runs.
Throughput is nearly identical at max effort, 58.8 tokens a second for Sol against 58.1 for Astra, but Sol reached its first token in 131 seconds against 334, and those times include thinking. At high effort Astra measured 37 seconds to first token and scored 51 on the index.
Pro at $23/month and up, including VIP and Elite, at 25 PT per 750 tokens of prompt plus reply. Replies are capped at 8,192 output tokens, and usage counts against a frontier text allowance shared with Claude Fable 5 and 5.1.
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