Nex AGI: Nex-N2.5-Pro (free) vs OpenAI: GPT-5.1-Codex-Mini
Neither wins outright: Nex AGI: Nex-N2.5-Pro (free) is the pick when cost matters at scale, OpenAI: GPT-5.1-Codex-Mini when you need to fit long inputs in one request.
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)
Nex AGI: Nex-N2.5-Pro (free)
OpenAI: GPT-5.1-Codex-Mini
Difference
Customer-support chatbot
50,000 conversations — each a 6-turn conversation (1,500 in / 400 out tokens)
$0
$58.75
Nex AGI: Nex-N2.5-Pro (free) saves $58.75
RAG search over documents
20,000 questions — each a question answered from ~8 retrieved passages (6,000 in / 500 out tokens)
$0
$50.00
Nex AGI: Nex-N2.5-Pro (free) saves $50.00
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)
$0
$54.00
Nex AGI: Nex-N2.5-Pro (free) saves $54.00
Batch summarisation
10,000 documents — each a 6,000-word report summarised to a page (8,000 in / 600 out tokens)
$0
$32.00
Nex AGI: Nex-N2.5-Pro (free) saves $32.00
Long-document analysis
500 documents — each a 150-page contract or codebase read in one pass (100,000 in / 2,000 out tokens)
$0
$14.50
Nex AGI: Nex-N2.5-Pro (free) saves $14.50
Capabilities side by side
Capability
Nex AGI: Nex-N2.5-Pro (free)
OpenAI: GPT-5.1-Codex-Mini
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
✓ Yes
read screenshots, charts and scanned pages
Audio input
—
—
take speech or audio directly
File / PDF input
—
—
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
✓ Yes
—
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
Nex AGI: Nex-N2.5-Pro (free): price unchanged since we started tracking it on 2026-09-09.
OpenAI: GPT-5.1-Codex-Mini: price unchanged since we started tracking it on 2026-03-10.
Which should you choose?
Choose Nex AGI: Nex-N2.5-Pro (free) if…
cost matters at scale — it is 100% cheaper on a typical 3:1 input/output mix ($0 vs $58.75 a month for 50,000 support chats)
you need log-probabilities — to read token confidence for classification and scoring; OpenAI: GPT-5.1-Codex-Mini does not advertise it
you generate long outputs in one go — up to 236K tokens (about 176,900 words) per response
you want to prototype at zero cost — a free variant is listed
you want the newer model — released 2026-09-08, 10 months after the other
Choose OpenAI: GPT-5.1-Codex-Mini if…
you need to fit long inputs in one request — 400K tokens is roughly 600 pages, against 393
you need built-in web search — to answer from live web results; Nex AGI: Nex-N2.5-Pro (free) does not advertise it
you need seed (reproducible sampling) — to repeat a generation for tests and evals; Nex AGI: Nex-N2.5-Pro (free) does not advertise it
Frequently asked questions
Is Nex AGI: Nex-N2.5-Pro (free) better than OpenAI: GPT-5.1-Codex-Mini?
Neither wins outright: Nex AGI: Nex-N2.5-Pro (free) is the pick when cost matters at scale, OpenAI: GPT-5.1-Codex-Mini when you need to fit long inputs in one request. In short: Nex AGI: Nex-N2.5-Pro (free) when cost matters at scale, you need log-probabilities, you generate long outputs in one go, you want to prototype at zero cost, you want the newer model; OpenAI: GPT-5.1-Codex-Mini when you need to fit long inputs in one request, you need built-in web search, you need seed (reproducible sampling).
Which is cheaper, Nex AGI: Nex-N2.5-Pro (free) or OpenAI: GPT-5.1-Codex-Mini?
Nex AGI: Nex-N2.5-Pro (free) is cheaper: $0 vs $0.69 per 1M tokens at a typical 3:1 input/output mix, 100% less. For 50,000 support conversations a month that is $0 against $58.75.
How much do Nex AGI: Nex-N2.5-Pro (free) and OpenAI: GPT-5.1-Codex-Mini cost per million tokens?
Nex AGI: Nex-N2.5-Pro (free) costs $0 per 1M input tokens and $0 per 1M output tokens; OpenAI: GPT-5.1-Codex-Mini costs $0.25 input and $2.00 output. Output tokens are billed separately, so long answers shift the gap.
Which has the bigger context window, Nex AGI: Nex-N2.5-Pro (free) or OpenAI: GPT-5.1-Codex-Mini?
OpenAI: GPT-5.1-Codex-Mini: 400K tokens, about 600 pages, against 262K (about 393 pages) for Nex AGI: Nex-N2.5-Pro (free).
Do Nex AGI: Nex-N2.5-Pro (free) and OpenAI: GPT-5.1-Codex-Mini support function calling and JSON output?
Can Nex AGI: Nex-N2.5-Pro (free) or OpenAI: GPT-5.1-Codex-Mini read images?
Yes, both accept image input.
Is Nex AGI: Nex-N2.5-Pro (free) or OpenAI: GPT-5.1-Codex-Mini free to use?
Nex AGI: Nex-N2.5-Pro (free) has a free variant (nex-agi/nex-n2.5-pro:free). Free variants usually carry tighter rate limits.
What is the maximum output length of Nex AGI: Nex-N2.5-Pro (free) and OpenAI: GPT-5.1-Codex-Mini?
Nex AGI: Nex-N2.5-Pro (free) can write up to 236K tokens (about 176,900 words) per response; OpenAI: GPT-5.1-Codex-Mini up to 128K (about 96,000 words).
When were Nex AGI: Nex-N2.5-Pro (free) and OpenAI: GPT-5.1-Codex-Mini released?
Nex AGI: Nex-N2.5-Pro (free) was listed on 2026-09-08; OpenAI: GPT-5.1-Codex-Mini on 2025-11-13.
Nex-N2.5 is an agentic model built to turn goals into working, verified outcomes. Its core strength is agentic coding within a visual feedback loop: it can explore codebases, implement multi-file...