GPT-5 is OpenAI's flagship language model, generally available since August 2025. It runs as the default ChatGPT model across all plans and ships in four API variants: gpt-5, gpt-5-mini, gpt-5-pro, and a 'thinking' mode picked automatically by a router. Per OpenAI's GPT-5 system card, the model hallucinates roughly 80% less than GPT-4o and scores 74.9% on SWE-bench Verified, the highest result of any major foundation model in 2026. ## May 2026 Update GPT-5 has been generally available since August 2025 and is now nine months into production. ChatGPT users got a smarter default model. Developers got three API tiers (mini, standard, pro) plus a router that picks 'thinking mode' automatically when a question is hard. Runbear now runs on GPT-5 via the OpenAI API, powering context assembly and automated actions across 2,000+ connected tools in Slack. The improvement in instruction following (GPT-5 scored 99% on COLLIE vs earlier baselines) shows up directly in how precisely Runbear agents route requests, draft responses, and take action. [See the Aloware case study](/content/posts/aloware-zoom-transcript-agent-case-study/index.html) for a real example: a Zoom transcript agent that logs CRM deals with a single emoji, built on this model layer. The rest of this post covers everything you need to know: what GPT-5 is, how it compares to prior models, availability, pricing, and what it means for ops teams using AI in Slack. ## What Is GPT-5? GPT-5 is OpenAI's most advanced language model yet—built to be more robust, reliable, and helpful than any of its predecessors. It delivers state-of-the-art accuracy on real-world tasks while significantly reducing hallucinations and deceptive responses. Designed with real workflows in mind, it powers real-time AI agents, developer tools, and enterprise copilots across platforms like Slack, HubSpot, and Microsoft Teams. ## Key Improvements in GPT-5 - State-of-the-art performance on leading AI benchmarks: - **Fewer hallucinations**: GPT-5 responses are up to **80%** more factual than previous models like GPT-4o or o3. - **Safer and more honest**: Reduced deceptive behavior in edge cases or underspecified prompts. - **Improved instruction following**: More reliable for agents, workflows, and multi-step tasks. - **Multimodal reasoning**: Enhanced capabilities across **text, image, video, and charts**. ## What makes GPT-5 different? Rather than a single monolithic model, GPT-5 introduces a router-based model architecture: - **GPT-5**: Fast, general-purpose response generation - **GPT-5 Thinking**: Deep reasoning for complex tasks - **GPT-5 Pro**: Long-context, high-precision model tuned for advanced applications These models are deployed intelligently behind the scenes, depending on query difficulty, user intent, and context. This allows GPT-5 to feel both fast and deeply capable—delivering expert-level answers where needed, while still handling everyday queries with speed and grace. ## Evaluations: How Smart Is GPT-5? ### Math Mastery GPT-5 dominates math evaluations: - **AIME 2025**: 94.6% (no tools) — new state-of-the-art. - **HMMT**: 96.7% (no tools), 100% (with tools). - **FrontierMath**: 26.3% → 32.1% with tool support. - **GPQA (PhD-level)**: 88.4% (no tools) → 89.4% (with thinking). ### Real-World Coding On practical software engineering and code editing benchmarks: - **SWE-bench Verified**: 74.9% accuracy (GPT-5) vs 69.1% (OpenAI o3) and 30.8% (GPT-4o). - **Aider Polyglot**: 88% accuracy (GPT-5), far ahead of all previous models. ### Instruction Following & Tool Use GPT-5 is vastly better at multi-step reasoning and agentic behaviors: - **Scale MultiChallenge (multi-turn)**: 69.6% vs GPT-4o's 40.3%. - **BrowseComp (search + browsing)**: 54.9% vs 49.7%. - **COLLIE (freeform following)**: 99.0% accuracy. ### Multimodal Understanding GPT-5 outperforms on visual, video, and diagram-based tasks: - **MMMU**: 84.2% vs GPT-4o's 72.2%. - **ERQA**: 65.7% vs 35.2% (GPT-4o). ### Health Conversations GPT-5 is the most accurate and least hallucinatory model for medical applications: - **HealthBench**: 67.2% vs GPT-4o's 32.0%. - **Hallucination Rate**: 1.6% (with thinking), down from GPT-4o's 15.8%. ### Economically Valuable Tasks GPT-5 beats both o3 and ChatGPT Agent on complex, real-world professional tasks: - Achieves **47.1%** wins over industry experts in internal benchmarks. ### Faster, More Efficient Thinking GPT-5 achieves better performance with fewer output tokens than OpenAI o3: - **50–80%** fewer tokens across reasoning, coding, and scientific benchmarks. ### Detailed Benchmarks ## Who is GPT-5 for? - **Business leaders & teams**: Analyze documents, monitor operations, and plan strategy with better context awareness and safer outputs. - **Developers**: Use GPT-5 to generate production-quality frontends, debug codebases, and automate software tasks. - **Healthcare professionals & patients**: Understand diagnoses and treatment options with greater clarity and proactive reasoning. - **Knowledge workers & writers**: Get help crafting thoughtful reports, articles, or even poetry—with deeper structure and emotional impact. ## Final Thoughts GPT-5 sets a new standard in reasoning, reliability, and real-world AI performance. With better benchmarks and lower hallucination rates, it's shaping up to be the most capable foundation model to date. Runbear agents are powered by GPT-5 via the OpenAI API. That means every context assembly, Slack response, and automated action your team runs through Runbear benefits from GPT-5's improved reasoning and lower hallucination rates.