GPT-4 and GPT-4o
GPT-4 (2023) was OpenAI's breakthrough large multimodal model that could accept images as well as text, and GPT-4o (2024) made it faster, cheaper, and natively able to handle audio, vision, and text in a single model.
Overview
Together they defined the modern era of ChatGPT.
Deep Dive
GPT-4, released in March 2023, was a major leap over GPT-3.5: it scored in the top percentiles on exams like the bar and AP tests, handled far longer prompts, and could reason about images. GPT-4 Turbo later added a 128k-token context window and cheaper pricing. In May 2024, OpenAI introduced GPT-4o, where the 'o' stands for 'omni', a single model trained end-to-end across text, audio, and vision. Earlier voice mode chained three separate models (speech-to-text, then GPT, then text-to-speech), adding lag; GPT-4o processes audio directly, enabling near-real-time spoken conversation with emotional tone and the ability to be interrupted. It is also roughly twice as fast and half the cost of GPT-4 Turbo via the API, and OpenAI made it available to free ChatGPT users, broadening access dramatically.
Technical Insight
Both are decoder-only Transformer models trained to predict the next token, then refined with reinforcement learning from human feedback (RLHF) to follow instructions and behave safely. The crucial advance in GPT-4o is end-to-end multimodality: instead of routing speech through separate transcription and synthesis models, one network ingests and emits audio tokens directly, preserving tone, timing, and non-verbal cues while slashing latency to roughly conversational speed (a few hundred milliseconds).
Strategic Impact
Vendor strategy
Vendor roadmaps influence what features your team can build next.
Cost and budget
Commercial terms and deployment options affect long-term cost and risk.
Risk and safety
Company incentives shape product defaults, safety posture, and openness.
The Future of GPT-4 and GPT-4o
GPT-4o set the template for fluid, real-time multimodal assistants, and OpenAI's successors are pushing further into reasoning (the o-series 'thinking' models that deliberate before answering), longer context, and agentic tool use. Expect lower costs, richer real-time voice and video interaction, tighter app and device integration, and models that fluidly switch between fast responses and slow, careful reasoning depending on task difficulty. Multimodal generation, producing images and audio natively, will keep expanding.
Real-World Implementation
Having a near-real-time spoken conversation with ChatGPT's Advanced Voice Mode, including interrupting it mid-sentence
Uploading a photo of a refrigerator's contents and asking GPT-4o to suggest recipes
Pasting a long legal contract into the 128k-token context window for summarization and risk-spotting
Using the vision capability to read and explain a chart, handwritten note, or screenshot of an error message
Risks & Guardrails
Launch announcements may outpace stability in real production workflows.
API pricing or policy shifts can break assumptions overnight.
Single-vendor dependency increases lock-in and migration costs.
Implementation Roadmap
Evaluate providers using your own tasks and datasets.
Review privacy, security, and legal terms before integration.
Maintain a fallback plan across models or vendors.
Monitor release notes so roadmap changes do not surprise teams.
Keep Exploring
Free newsletter
Keep up with AI in 3 minutes a day
One short email each weekday with the three AI stories that actually matter. Free forever, no ads.
One email each weekday. Unsubscribe in one click. We never sell or share your address.
Test yourself
Take the GPT-4 and GPT-4o quiz
Instant feedback on every answer, and a shareable certificate with a verifiable ID once you pass a course.
Support free AI education. AI Understanding is a 501(c)(3) nonprofit — no ads, no paywall, ever. Make a donation
Next guide
OpenAI GPT-4.5 and GPT-5
Frequently asked questions
What is GPT-4 and GPT-4o?
GPT-4 (2023) was OpenAI's breakthrough large multimodal model that could accept images as well as text, and GPT-4o (2024) made it faster, cheaper, and natively able to handle audio, vision, and text in a single model. Together they defined the modern era of ChatGPT.
What does the 'o' in GPT-4o stand for?
The 'o' stands for 'omni,' reflecting that GPT-4o is a single model handling text, audio, and vision together.
Why is GPT-4o's voice mode faster than GPT-4's earlier voice feature?
Earlier voice mode chained three separate models, adding lag. GPT-4o handles audio end-to-end in a single network, cutting latency to near-conversational speed.
What major new input type did GPT-4 introduce over GPT-3.5 at launch?
GPT-4 was a large multimodal model that could accept image inputs in addition to text, a capability GPT-3.5 lacked.
What context window size did GPT-4 Turbo offer?
GPT-4 Turbo expanded the context window to 128k tokens, allowing much longer documents and conversations.
Which training technique is used to make GPT-4 and GPT-4o follow instructions and behave safely?
After next-token pretraining, the models are refined with RLHF, using human preferences to shape helpful, safe instruction-following behavior.