Choose AionLabs: Aion 3.5 if…
- cost matters at scale — it is 91% cheaper on a typical 3:1 input/output mix ($345 vs $3,525 a month for 50,000 support chats)
- you want the newer model — released 2026-09-23, 12 months after the other
AionLabs: Aion 3.5 vs OpenAI: GPT-5 Pro
Neither wins outright: AionLabs: Aion 3.5 is the pick when cost matters at scale, OpenAI: GPT-5 Pro when you need to fit long inputs in one request.
Key numbers
| Spec | AionLabs: Aion 3.5 | OpenAI: GPT-5 Pro |
|---|---|---|
| Provider | Aion Labs | OpenAI |
| Input price (per 1M tokens) | $3.00 | $15.00 |
| Output price (per 1M tokens) | $6.00 | $120 |
| Blended price (3:1 input/output) | $3.75 | $41.25 |
| Cheaper than … of all models we track | 17% | 1% |
| Context window | 262K tokens (~393 pages) | 400K tokens (~600 pages) |
| Larger context than … of all models | 47% | 63% |
| Max output per response | 33K tokens (~24,600 words) | 128K tokens (~96,000 words) |
| Input types | text | image, text, file |
| Output types | text | text |
| Free variant | No | No |
| Listed since | 2026-09-23 | 2025-10-06 |
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What it costs for real workloads
Monthly cost at list price for five common workloads. Token counts per unit are stated so you can scale them to your own traffic. A workload that does not fit a model's context window is marked rather than priced.
| Workload (per month) | AionLabs: Aion 3.5 | OpenAI: GPT-5 Pro | Difference |
|---|---|---|---|
| Customer-support chatbot 50,000 conversations — each a 6-turn conversation (1,500 in / 400 out tokens) | $345 | $3,525 | AionLabs: Aion 3.5 saves $3,180 |
| RAG search over documents 20,000 questions — each a question answered from ~8 retrieved passages (6,000 in / 500 out tokens) | $420 | $3,000 | AionLabs: Aion 3.5 saves $2,580 |
| Coding / tool-using agent 2,000 tasks — each a multi-step task with tool calls and file context (60,000 in / 6,000 out tokens) | $432 | $3,240 | AionLabs: Aion 3.5 saves $2,808 |
| Batch summarisation 10,000 documents — each a 6,000-word report summarised to a page (8,000 in / 600 out tokens) | $276 | $1,920 | AionLabs: Aion 3.5 saves $1,644 |
| Long-document analysis 500 documents — each a 150-page contract or codebase read in one pass (100,000 in / 2,000 out tokens) | $156 | $870 | AionLabs: Aion 3.5 saves $714 |
Capabilities side by side
| Capability | AionLabs: Aion 3.5 | OpenAI: GPT-5 Pro | What it lets you do |
|---|---|---|---|
| Tool / function calling | ✓ Yes | ✓ Yes | call your APIs and run agent loops |
| Structured output (JSON schema) | ✓ Yes | ✓ Yes | return JSON that validates against your schema |
| Reasoning / thinking mode | ✓ Yes | ✓ Yes | spend extra tokens thinking before answering hard problems |
| Image input | — | ✓ Yes | read screenshots, charts and scanned pages |
| Audio input | — | — | take speech or audio directly |
| File / PDF input | — | ✓ Yes | accept documents without your own parsing step |
| Image output | — | — | generate images, not just text |
| Built-in web search | — | ✓ Yes | answer from live web results |
| Seed (reproducible sampling) | — | ✓ Yes | repeat a generation for tests and evals |
| Log-probabilities | — | — | read token confidence for classification and scoring |
From each model's published parameters and input/output types. “—” means not advertised, not proven absent.
Price history
- AionLabs: Aion 3.5: price unchanged since we started tracking it on 2026-09-24.
- OpenAI: GPT-5 Pro: price unchanged since we started tracking it on 2026-03-10.
Which should you choose?
Choose OpenAI: GPT-5 Pro if…
- you need to fit long inputs in one request — 400K tokens is roughly 600 pages, against 393
- you need image input — to read screenshots, charts and scanned pages; AionLabs: Aion 3.5 does not advertise it
- you need file / PDF input — to accept documents without your own parsing step; AionLabs: Aion 3.5 does not advertise it
- you need built-in web search — to answer from live web results; AionLabs: Aion 3.5 does not advertise it
- you need seed (reproducible sampling) — to repeat a generation for tests and evals; AionLabs: Aion 3.5 does not advertise it
- you generate long outputs in one go — up to 128K tokens (about 96,000 words) per response
Frequently asked questions
Is AionLabs: Aion 3.5 better than OpenAI: GPT-5 Pro?
Neither wins outright: AionLabs: Aion 3.5 is the pick when cost matters at scale, OpenAI: GPT-5 Pro when you need to fit long inputs in one request. In short: AionLabs: Aion 3.5 when cost matters at scale, you want the newer model; OpenAI: GPT-5 Pro when you need to fit long inputs in one request, you need image input, you need file / PDF input, you need built-in web search, you need seed (reproducible sampling), you generate long outputs in one go.
Which is cheaper, AionLabs: Aion 3.5 or OpenAI: GPT-5 Pro?
AionLabs: Aion 3.5 is cheaper: $3.75 vs $41.25 per 1M tokens at a typical 3:1 input/output mix, 91% less. For 50,000 support conversations a month that is $345 against $3,525.
How much do AionLabs: Aion 3.5 and OpenAI: GPT-5 Pro cost per million tokens?
AionLabs: Aion 3.5 costs $3.00 per 1M input tokens and $6.00 per 1M output tokens; OpenAI: GPT-5 Pro costs $15.00 input and $120 output. Output tokens are billed separately, so long answers shift the gap.
Which has the bigger context window, AionLabs: Aion 3.5 or OpenAI: GPT-5 Pro?
OpenAI: GPT-5 Pro: 400K tokens, about 600 pages, against 262K (about 393 pages) for AionLabs: Aion 3.5.
Do AionLabs: Aion 3.5 and OpenAI: GPT-5 Pro support function calling and JSON output?
Tool calling — AionLabs: Aion 3.5: yes, OpenAI: GPT-5 Pro: yes. JSON-schema structured output — AionLabs: Aion 3.5: yes, OpenAI: GPT-5 Pro: yes.
Can AionLabs: Aion 3.5 or OpenAI: GPT-5 Pro read images?
Only OpenAI: GPT-5 Pro accepts image input; AionLabs: Aion 3.5 is text-only for input.
Is AionLabs: Aion 3.5 or OpenAI: GPT-5 Pro free to use?
No free variant is listed for either; both are pay-per-token.
What is the maximum output length of AionLabs: Aion 3.5 and OpenAI: GPT-5 Pro?
AionLabs: Aion 3.5 can write up to 33K tokens (about 24,600 words) per response; OpenAI: GPT-5 Pro up to 128K (about 96,000 words).
When were AionLabs: Aion 3.5 and OpenAI: GPT-5 Pro released?
AionLabs: Aion 3.5 was listed on 2026-09-23; OpenAI: GPT-5 Pro on 2025-10-06.
About the two models
AionLabs: Aion 3.5
Aion 3.5 is a multi-model roleplaying and storytelling system from AionLabs, built on the GLM family of models. It uses a collaborative generation process in which multiple specialized models each...
Full AionLabs: Aion 3.5 specs →OpenAI: GPT-5 Pro
GPT-5 Pro is OpenAI’s most advanced model, offering major improvements in reasoning, code quality, and user experience. It is optimized for complex tasks that require step-by-step reasoning, instruction following, and...
Full OpenAI: GPT-5 Pro specs →