ChatGPT deep review: GPT-5 reasoning, Codex IDE, Sora, Plus vs Pro, and region limits

GPT-5 is not a single model. It is a router in front of a reasoning layer that decides per prompt whether to call the fast path, the deep-reasoning path, or a tool-augmented path. The reasoning layer is what gives GPT-5 its 'thinking' before the answer: chain-of-thought traces, self-critique, and multi-step planning.

From a network perspective, the reasoning layer is a separate endpoint with stricter abuse controls. If your exit IP is on a known datacenter ASN, the router may silently degrade you to the fast path: the answer comes back faster, with no thinking trace, and output quality drops. You see the right model name and never see the downgrade.

Codex is the coding-agent arm of GPT-5. The IDE integration runs as a local agent that talks to OpenAI's backend through the same path your browser uses. If ChatGPT.com works, Codex works. If ChatGPT.com is throttled or routed to a different region, Codex is too.

Two practical implications. First, IPCombo's per-target IP column shows whether openai.com is hitting the right region for you — and that is the same region Codex will use. Second, Codex sessions are billed against your ChatGPT account, so a region mismatch on the account side blocks Codex even when the IP is correct.

Sora is OpenAI's video model, gated behind the same ChatGPT account. The Sora UI lives inside ChatGPT.com, so routing is identical. But Sora has its own quota: Plus gets a small number of generations per day, Pro gets higher limits and priority queue.

The hidden gotcha: Sora pulls thumbnails and generation previews from a separate CDN, and that CDN is region-aware. If your IP is in a region Sora does not serve previews to, the UI loads but previews are blank or 403. The connectivity matrix is the only place this surfaces — ChatGPT itself does not expose it.

ChatGPT Plus is $20/month. ChatGPT Pro is $200/month. The 10x price buys you: unlimited GPT-5 deep reasoning (Plus has a daily cap that resets unpredictably), Sora Pro generation limits (about 10x), priority queue during peak hours, and early access to agentic features (Operator, Codex agent mode).

For most users, Plus is enough. Pro is for people who hit the reasoning cap daily and need Sora for actual production work. The decision is rarely about features — both tiers ship the same model — and almost always about quotas.

GPT-5 reasoning and Sora are restricted in a small set of countries and on a small set of ASNs. The country list is published; the ASN list is not. From what we have observed: full access works from US, JP, KR, SG residential or mobile IPs. Datacenter IPs in those regions get the model but lose reasoning. Other regions see a partial feature set.

How to test: run IPCombo with both ChatGPT.com and the Sora preview CDN as targets. If the per-target IP column shows a residential or mobile exit in US/JP/KR/SG, you are in the green zone. If it shows a datacenter exit, you can use Plus chat but reasoning will be silently throttled. The diagnosis card tells you which class your exit is.