GPT-5.1 Chat

gpt-5.1-chat-latest API, is OpenAI’s GPT-5.1 Instant that is the low-latency variant of the newly released GPT-5.1 family (announced November 12, 2025). It’s designed to deliver the “most-used” ChatGPT experience with faster turn-taking, warmer conversational tone defaults, improved instruction following, and a built-in adaptive-reasoning capability that decides when to reply immediately and when to spend extra compute to “think” through harder queries.

Basic information & features

• Warmer, more conversational default tone and expanded tone/personalization presets to match user preferences (examples: Professional, Friendly, Candid, Quirky, Efficient, Nerdy, Cynical).
• Adaptive reasoning: the model decides when to take extra reasoning steps before answering; Instant aims to be fast on most everyday prompts while still using extra effort when appropriate.
• Improved instruction-following (fewer misunderstandings on multi-step prompts) and generally reduced jargon for better user comprehension (especially in the Thinking variant).
• Designed for real-time UX: streaming responses, low token-roundtrip latency useful for voice assistants, live transcription, and highly interactive conversational apps.

Technical details (developer-facing)

• API model identifiers: OpenAI will expose Instant in the API under the chat-style identifier gpt-5.1-chat-latest (Instant) and gpt-5.1 for Thinking (per OpenAI’s release notes). Use the Responses API endpoint for best efficiency.
• Response API & parameters: The GPT-5 family (including 5.1) is best used via the newer Responses API. Typical options you’ll pass include model name, input/messages, and optional control parameters like verbosity / reasoning (effort) that tune how much internal reasoning the model attempts before responding (assuming the platform follows the same parameter conventions introduced with GPT-5). For highly interactive apps, enable streaming replies.
• Adaptive reasoning behaviour: Instant is tuned to favor quick replies but has light adaptive reasoning—it will allocate slightly more compute on tougher prompts (math, coding, multi-step reasoning) to reduce errors while keeping average latency low. GPT-5.1 Thinking will spend more compute on harder problems and less on trivial ones.

Benchmark & safety performance

GPT-5.1 Instant is tuned to keep responses fast while improving math and coding evals (AIME 2025, Codeforces improvements were specifically noted by OpenAI).

OpenAI published a GPT-5.1 System Card addendum with production benchmark metrics and targeted safety evaluations. Key figures (Production Benchmarks, higher = better, not_unsafe metric):

• Illicit / non-violent (not_unsafe) — gpt-5.1-instant: 0.853.
• Personal data — gpt-5.1-instant: 1.000 (perfect on this benchmark).
• Harassment — gpt-5.1-instant: 0.836.
• Mental health (new eval) — gpt-5.1-instant: 0.883.
• StrongReject (jailbreak robustness, not_unsafe) — gpt-5.1-instant: 0.976 (shows strong robustness to adversarial jailbreaks compared with older instant checkpoints).

Typical and recommended use cases for GPT-5.1 Instant

1. Chatbots & conversational UIs — customer support chat, sales assistants, and product guides where low latency preserves conversation flow.
2. Voice assistants / streaming replies — streaming partial outputs to a UI or TTS engine for sub-second interactions.
3. Summarization, rephrasing, message drafting — quick transformations that benefit from a warmer, user-friendly tone.
4. Light coding help and inline debugging — for quick code snippets and suggestions; use Thinking for deeper bug hunts. (Test on your codebase.)
5. Agent front-ends and retrieval-augmented workflows — where you want fast responses combined with occasional deeper reasoning/tool calls. Use the adaptive-reasoning behavior to balance cost vs. depth.

Comparison with other models

• GPT-5.1 vs GPT-5: GPT-5.1 is a tuned upgrade — warmer default tone, improved instruction following, and adaptive reasoning. OpenAI positions 5.1 as strictly better in the areas they targeted, but retains GPT-5 in a legacy menu for transition/compatibility.
• GPT-5.1 vs GPT-4.1 / GPT-4.5 / GPT-4o: GPT-5 family still targets higher reasoning and coding performance than GPT-4.x series; GPT-4.1 remains relevant for very long contexts or cost-sensitive deployments. Reporters emphasize GPT-5/5.1 lead on hard math/coding benchmarks, but exact per-task advantages depend on the benchmark.
• GPT-5.1 vs Claude / Gemini / other rivals: early commentary frames GPT-5.1 as a response to user feedback (personality + capability). Competitors (Anthropic’s Claude Sonnet series, Google’s Gemini 3 Pro, Baidu’s ERNIE variants) emphasize different tradeoffs (safety-first, multimodality, massive contexts). For technical customers, evaluate across cost, latency, safety behavior on your workloads (prompts + tool calls + domain data).