GPT-5.1 is here: how it compares to GPT-5

Try GPT-5.1 out here: GPT-5.1 with tools and coding canvas and Powered by OpenAI GPT-5.1 .

As of November 13, 2025, GPT-5.1 is rolling out inside ChatGPT for paying users and gradually for free accounts. API access via the `gpt-5.1-chat-latest` (Instant) and `gpt-5.1` (Thinking) endpoints is slated for this week, but many developers still won’t see it in their dashboards yet. The context window clocks in at 128K tokens for GPT-5.1 Instant and 196K for GPT-5.1 Thinking on supported paid plans.

A Soft Reboot After GPT-5’s Awkward Debut

GPT-5.1 isn’t a new generation; it’s a do-over. GPT-5 launched in August with great expectations and a weird hangover: some power users felt it was colder than GPT-4o and occasionally less reliable on math and code, prompting a surprising wave of “can I get 4o back?” nostalgia.

OpenAI’s answer is GPT-5.1: two refreshed variants, Instant and Thinking, wrapped in a new “GPT-5.1 Auto” router that decides which one to run per request. The public story is clear: make ChatGPT smarter, but also make it feel less like a committee of lawyers and more like a human being you actually want to talk to.

On paper, GPT-5.1 is still GPT-5’s architecture, data and safety stack. In practice, the 5.1 tag hides a lot of engineering: adaptive reasoning, better instruction-following, expanded tone controls, and a routing layer that tries to spend compute where it matters instead of spraying FLOPs at every prompt.

Adaptive Reasoning: A Thinking Budget, Not a Fixed Timer

The headline change is adaptive reasoning. GPT-5.1 doesn’t think for a fixed amount of time anymore; it dynamically decides how much “inner monologue” to allocate before answering. Ask it to name three dog breeds and it fires back almost instantly. Hand it a messy algorithm design problem or an AIME-style math puzzle and it quietly spins up extra reasoning steps before committing to an answer.

OpenAI says this shows up clearly on hard benchmarks like AIME 2025 and Codeforces problem sets, where GPT-5.1 scores noticeably higher than GPT-5 without becoming glacial. Independent write-ups echo that story: reviewers describe fewer “off-by-one” style math blunders and more coherent chains of reasoning on competition-style tasks, particularly when using the Thinking mode.

Under the hood, GPT-5.1 Thinking exposes gradations of effort — “Light”, “Standard”, “Extended”, “Heavy” — giving power users an actual dial instead of a mystery box. Most people stick to Standard; agent frameworks and researchers are already cranking it up for difficult proofs, data analysis, and long-horizon planning where extra seconds pay off.

The net effect is surprisingly human: GPT-5.1 behaves like someone who answers small talk instantly but pauses and thinks when you throw them a PhD qualifier question, instead of blurting out the first plausible-sounding thing.

Coding and Math: Less Vibes, More Results

If GPT-5 sometimes felt like it was “vibe-coding” its way through problems, GPT-5.1 is closer to a meticulous senior dev. Early testers hammering it with LeetCode-plus-Codeforces style suites report:

  • Fewer silent logic errors in otherwise clean-looking code
  • Better handling of edge cases and tricky input distributions
  • More willingness to refactor and optimize, not just patch a bug in place

Multiple independent blogs and newsletters describe GPT-5.1 as a return to form compared with GPT-5 for programming help, especially in long sessions where earlier models would drift or forget constraints halfway through a refactor. Researchers probing it with research-level math problems report crisper step-by-step derivations and fewer “hand-wavy” leaps over the hard bits, particularly in the Thinking mode.

Is it now unambiguously top of the heap? Not quite; some showdown posts still see Anthropic’s and Google’s latest models edging ahead on certain long-horizon reasoning tests, and open-source challengers continue to nibble at the low-latency coding niche. But where GPT-5 occasionally left power users longing for GPT-4-era reliability, GPT-5.1 largely plugs those gaps — and does so without turning everyday chats into a slog.

From Chatbot to Presence: Eight Personalities and Fine-Grained Tone

The other half of the upgrade is emotional, not mathematical. GPT-5.1 simply sounds different.

GPT-5 had a tendency to come off clipped, cautious and a little distant. GPT-5.1 Instant, by contrast, starts from a warmer baseline: slightly more playful wording, a bit more empathy, less pseudo-corporate stiffness. Ask it about burnout and it’s more likely to respond with something like “You’re not alone in feeling this — let’s unpack what’s going on,” instead of dropping a sterile bullet list of coping techniques.

This isn’t just vague “tone tuning.” ChatGPT now ships with eight built-in personality presets — Default, Professional, Friendly, Candid, Quirky, Efficient, Nerdy, and Cynical — replacing the earlier, simpler style toggles. You pick the vibe; the underlying IQ stays the same. Want a polished corporate assistant? Flip to Professional. Prefer a nerdy explainer that happily dives into side-quests and references papers? Nerdy it is.

On top of those presets, OpenAI is quietly testing sliders for how warm, concise, or emoji-heavy you want replies to be, alongside better adherence to custom instructions. The goal is obvious: reduce the amount of prompt-engineering gymnastics needed to get the model to “sound right,” whether you’re building a customer-support bot or a tutoring companion.

GPT-5.1 Auto: One Button, Two Brains

Underneath the ChatGPT UI, GPT-5.1 really comes as a trio:

  • GPT-5.1 Instant – fast, chatty default with light adaptive reasoning.
  • GPT-5.1 Thinking – deeper, more expensive reasoning for hard tasks.
  • GPT-5.1 Auto – a router that decides which of the two should answer.

Select GPT-5.1 in ChatGPT and you’re effectively talking to Auto. It watches your prompts, past turns and historical patterns of what users pick manually, then chooses Instant or Thinking for you. When it does spin up the reasoning mode, you get a slimmed-down preview of its thought process and a “Answer now” button if you’d rather trade quality for speed.

For heavy users, the context story is straightforward but important:

  • GPT-5.1 Instant: up to 128K tokens
  • GPT-5.1 Thinking: up to 196K tokens

Both are a step up from the early GPT-4 era, but still shy of the 256K context many testers observed on the mysterious Polaris Alpha model that appeared on OpenRouter shortly before this launch.

API Story: `gpt-5.1-chat-latest`, `gpt-5.1` and What’s Next

For now, GPT-5.1 is a ChatGPT-first release. Paid users on Plus, Pro, Go, Business, Enterprise and Edu plans are getting it first, with free and logged-out users following as rollout stabilizes. Free tier accounts get a metered number of GPT-5.1 messages before falling back to a lighter model.

OpenAI says both variants are coming to the API “later this week” as:

  • `gpt-5.1-chat-latest` – the Instant model
  • `gpt-5.1` – the Thinking model, with adaptive reasoning enabled

Those model IDs now show up in documentation and early ecosystem guides, but availability is still in the middle of a staggered rollout — some developers can already hit them; others just see the names in docs and marketing. If you’re migrating from GPT-5, the intent is mostly drop-in replacement: same generation, better behavior, with GPT-5 remaining under a Legacy dropdown for roughly three months.

From a builder’s perspective, the big win isn’t a new maximum context or a radically different API; it’s the combination of:

  • Adaptive reasoning that cuts “hallucinated” answers on hard tasks
  • Stronger instruction-following, especially with constrained formats
  • Personality control that can be wired directly into app settings or user profiles

Polaris Alpha: The Shadow That Arrived First

Weeks before the official GPT-5.1 blog post, a stealth model called Polaris Alpha quietly appeared on OpenRouter with a 256K context window and startlingly strong reasoning benchmarks. It behaved suspiciously like an upgraded GPT-5: similar style, noticeably better performance, very high rate limits. Cue the speculation.

Independent analysts, Medium posts and podcasts quickly converged on the same theory: Polaris Alpha was GPT-5.1 Thinking in disguise, used to soak up real-world traffic before the public announcement. The pattern would fit OpenAI’s earlier codenames (Horizon Alpha/Beta preceding GPT-5) and matches anecdotal benchmark traces that put Polaris squarely between GPT-5 and the new 5.1 release. OpenAI, predictably, isn’t confirming any of this — but the timeline is hard to ignore.

If that narrative is right, you’ve already seen GPT-5.1 in the wild: it just shipped under someone else’s starry codename first.

Tools, Agents and “Software Inside the Conversation”

GPT-5.1 doesn’t land in a vacuum. It arrives alongside OpenAI’s push to turn ChatGPT into a full agentic workspace: Apps SDK, AgentKit, function calling, browser tools, Python sandboxes — all the scaffolding needed for “software that lives in the chat box.”

The new models are tuned to lean into that world. They’re better at deciding when to call tools, more robust when juggling multi-step workflows (e.g., run code → inspect output → patch → re-run), and less likely to hallucinate external facts instead of just asking the browser. Practically, that means fewer broken chains when you ask an assistant to:

  • Debug a failing test suite end-to-end
  • Pull live pricing, then build a comparison table
  • Run basic data analysis in a notebook-style loop

Agent builders are already reporting smoother runs and fewer “forgot to call the tool” failures compared to early GPT-5 setups.

Safety, Tone and the Tightrope Walk

There is a catch. GPT-5.1’s system card addendum quietly notes some small regressions in specific safety evaluations, particularly around sensitive topics like violence and mental health when using the deeper reasoning mode. Outside reviewers have also noticed that 5.1 can feel marginally more blunt or “unfiltered” in certain edge cases — a side-effect, perhaps, of dialing back the over-cautious guardrails that frustrated many GPT-5 users.

OpenAI’s pitch is that this is a conscious trade-off: models that are less annoying and more candid, while still staying within their overall safety envelope. The company says it is iterating on mitigations without rolling back the warmth and directness people clearly prefer. For the vast majority of everyday usage — coding, math, writing, research — GPT-5.1 simply feels more capable and less constrained than GPT-5, without obviously veering into unsafe territory.

The Competitive Backdrop: Claude, Gemini, Grok & the Rest

If GPT-4 defined an era where OpenAI felt comfortably ahead, GPT-5.1 lands in a very different landscape. Anthropic’s Claude 4/4.5 family, Google’s upcoming Gemini 3, xAI’s Grok and a growing wave of Chinese and open-source models are all pushing hard on reasoning, coding and long-context use cases.

Notably, OpenAI has not published a big flashy benchmark table this time. Instead, the message from both official materials and independent coverage is pragmatic: GPT-5.1 is an iterative but meaningful improvement designed to fix GPT-5’s missteps, tighten the perceived gap with Claude and Gemini in coding and math, and keep ChatGPT in pole position as the assistant people actually reach for every day.

In other words, GPT-5.1 isn’t trying to “win the internet” with a single knockout chart. It’s trying to make sure you don’t feel tempted to switch tabs.

Verdict: Not a New Era, But a Much Better Everyday Companion

GPT-5.1 delivers what GPT-5 promised but only partially delivered:

  • Smarter reasoning that scales up effort on hard tasks instead of guessing confidently.
  • More dependable coding and math, especially in the Thinking mode.
  • A warmer, more steerable personality, backed by eight presets and finer tone controls.
  • A cleaner developer story, with clear model IDs, adaptive reasoning and better instruction-following for structured outputs.

It’s not a paradigm shift, and OpenAI isn’t pretending it is. GPT-5.1 is a carefully targeted refinement of the GPT-5 generation that restores confidence for power users while making the default ChatGPT experience feel more human and less brittle. For anyone who lives in code, math, long research chats or agentic workflows, that’s exactly the kind of upgrade that matters.

The AI race will move on - Gemini 3, future Claude releases and whatever comes after Polaris are already looming. But right now, GPT-5.1 redraws the line for what a general-purpose assistant should feel like: a system that can reason hard, follow instructions, adapt its tone to you, and still answer in a fraction of a second when all you wanted was the name of that actor from that movie you half-remember.

For the first time since GPT-5 launched, it feels like the flagship model and the flagship experience are finally in sync.

For more information, visit GPT-5.1 Official Page and OpenAI's GPT-5.1.