Nex-N2.5 Pro vs GPT-5.6 Sol: The Newcomer's Vendor Number Trails the Incumbent's Independent One

Put the one benchmark where both have a number side by side and the order of operations is wrong for a launch. Nex-AGI's card gives Nex-N2.5 Pro a 56.4 on OSWorld-2, measured on the alliance's own NexCUA harness, which the public has not seen. BenchLM's OSWorld 2.0 leaderboard, updated August 29, puts GPT-5.6 Sol at 62.6 — an independent number that beats the newcomer's vendor number outright. On the day-old model's home turf — screen-reading computer use, the one thing it is purpose-built for — the mature generalist it is being compared with does not even need an asterisk to come out ahead. Nex-N2.5 Pro vs GPT-5.6 Sol is not a close contest on any dimension that has been measured by someone other than the newcomer's maker. It is a case study in what a production record is worth, and it is worth reading for that reason alone.

The two models are barely rivals in intent. Nex-N2.5 Pro, announced September 8, 2026, is a 397-billion-parameter sparse mixture-of-experts model with roughly 17 billion active parameters, multimodal (text and image in, text out), post-trained from Qwen3.5 lineage, and built to operate computers and browsers through a visual feedback loop. Its Apache-2.0 weights are still marked "coming soon" on Hugging Face, and its only live builds are free hosted endpoints Nex-AGI links from its card. GPT-5.6 Sol is OpenAI's flagship for "the hardest work" — deep multi-step reasoning, large-scale software engineering, and long-horizon agentic workflows — in the API since July 9, closed-weights, and now carrying the weight of having been the frontier reference point until OpenAI shipped GPT-6 Astra on September 3. Where Nex-N2.5 Pro is a specialist that has not shipped its own weights, GPT-5.6 Sol is a proven generalist that has shipped for two months to the most demanding production traffic in the industry.

GPT-5.6 Sol is the model with a file

Start with what Sol has that Nex-N2.5 Pro does not: a record. Since July 9, GPT-5.6 Sol has been run through independent harnesses, hammered by security researchers, and absorbed into agent frameworks and Codex workflows. Its independent measurements are deep and public: 61 on the Artificial Analysis Intelligence Index at max reasoning, 88.0 on Terminal-Bench 2.1 and 73.0 on DeepSWE measured by the same independent harness, and a measured output speed around 71 tokens per second with a cost of roughly $0.95 per Intelligence Index task. None of that makes it unbeatable — OpenAI has since positioned GPT-6 Astra above it — but every one of those numbers is a measurement someone other than OpenAI produced. Nex-N2.5 Pro has no independent entry anywhere, for a structural reason: no one outside the alliance can run it.

The one benchmark where both have a number

The OSWorld comparison is the cleanest read available, so it deserves its caveats stated before it is used. Nex-N2.5 Pro's 56.4 is Nex-AGI's own measurement on OSWorld-2 through its NexCUA harness. GPT-5.6 Sol's 62.6 comes from BenchLM's OSWorld 2.0 leaderboard, a third-party snapshot dated August 29, 2026, which lists fifteen models and places Claude Opus 5 first at 70.6 with GPT-5.6 Sol second at 62.6 and GPT-5.6 Terra third at 50.2. "OSWorld-2" and "OSWorld 2.0" are close kin but not proven identical, so the exact four-to-six-point gap should be read as directional rather than precise. What survives the caveats is the ordering: by the best number each side can produce, an independent Sol figure beats a vendor Nex figure on the benchmark Nex chose to publish. A newcomer whose own number is lower than the incumbent's independent number has not made a compelling case for switching.

Spec envelopes

The rest of the spec sheet runs in the same direction:

• Released — Nex-N2.5 Pro: September 8, 2026 (hosted endpoints live, weights pending). GPT-5.6 Sol: July 9, 2026, generally available.

• Scale — Nex-N2.5 Pro: 397B total / ~17B active MoE. GPT-5.6 Sol: parameter count undisclosed.

• Modality — Nex-N2.5 Pro: text and image in, text out, computer-use vision loop. GPT-5.6 Sol: text, image and file input, text output, with tool calling and JSON mode.

• Context / output — Nex-N2.5 Pro: 262,144-token context. GPT-5.6 Sol: ~1.05M-token context, 128K output ceiling.

• Reasoning control — Nex-N2.5 Pro: none / medium (adaptive, default) / high. GPT-5.6 Sol: reasoning effort up to max, plus a separate fast processing tier.

• Weights — Nex-N2.5 Pro: Apache-2.0, coming soon. GPT-5.6 Sol: closed.

• Price per 1M tokens — Nex-N2.5 Pro: free hosted tier, no list price. GPT-5.6 Sol: $4.00 / $20.00 promotional list since August 21, $0.40 cached input, re-tiering to $8.00 / $30.00 above 272K input tokens.

Sol's ~1.05M-token context and 128K output ceiling dwarf Nex-N2.5 Pro's 262K window for long-horizon work, and Sol's price, while far from cheap, is a settled number a budget can model. Nex-N2.5 Pro's free tier is the only number on its side, and it is not a price.

What a day-old score is worth

Every benchmark claim attached to Nex-N2.5 Pro — OSWorld-2 at 56.4, Terminal-Bench 2.1 at 82.7, SWE-Bench Pro at 61.2, BrowseComp at 89.7 — shares one property: Nex-AGI produced it, through a harness the alliance says it will open-source but has not yet. None of those figures has been independently reproduced, because none can be: the weights are not downloadable, and no date is attached to the "coming soon" banner. That matters more in this matchup than in most, because the model Nex-N2.5 Pro is being compared with has the longest independent record in the industry. When the challenger's entire evidence base is self-reported and the incumbent's is not, the burden of proof sits entirely on the challenger, and a free endpoint does not discharge it. The moment the shards land and an independent lab runs Nex-N2.5 Pro, this article's numbers become checkable and the comparison becomes real. Until then, "day-old score" is the accurate phrase — a score that cannot be inspected on a model that cannot be run.

Price, route, and the shape of the decision

Cost is where the two sides are least comparable, because only one side has a cost. GPT-5.6 Sol's $4.00 / $20.00 rate is OpenAI's promotional list price in effect since August 21 and stated to run at least through November 21, down from $5.00 / $30.00 — a cut that made the flagship dramatically more affordable for high-volume agentic work, and one that a pass-through router reflects the same day OpenAI makes it. Sol is on OrcaRouter at that list price, no markup, with the batch tier and fast tier available behind the same API key as 200+ other models, so a team can route the requests that need OpenAI's depth to Sol and cheaper models to everything else. Nex-N2.5 Pro has no list price, only its free hosted endpoints — which is a fine way to evaluate a model and a poor basis for a production budget. You cannot plan a spend around a number that does not exist, and you cannot plan an architecture around weights that have not been released.

The decision this matchup actually forces is about risk, not capability. If you need a model that will still be there next quarter, with a known price, a known failure profile, and months of adversarial testing behind it, GPT-5.6 Sol is the rational choice — and OpenAI's launch of GPT-6 Astra above it only strengthens the case, because Sol is now the proven workhorse with the price cut aimed squarely at production volume. If you are building computer-use agents on open weights and can afford to wait for something verifiable, Nex-N2.5 Pro is worth watching — a 17B-active multimodal specialist is exactly the shape of model that has repeatedly undercut the closed frontier on cost. But watching is the operative word. On every dimension measured by anyone other than its maker, Nex-N2.5 Pro trails the model with the file, and until the weights drop, that is where the comparison ends.