What multimodal means and why it matters
A multimodal model takes more than just text as input — typically text plus images, and increasingly audio and video — and reasons over them together in one context. That collapses pipelines that used to need separate tools: instead of OCR-then-LLM or speech-to-text-then-LLM, you hand the model a screenshot, a chart, a scanned invoice, or an audio clip and ask about it directly. A separate capability is output: some models can also generate images or speech, which is distinct from being able to understand them.
Vision and document understanding
For reading images, charts, screenshots, and documents, GPT-4o and Gemini 1.5 Pro are both excellent general-purpose choices. Claude 3.5 Sonnet is particularly strong at dense documents, diagrams, and UI screenshots, and is a favourite for parsing complex PDFs and reasoning about their content. Gemini 1.5 Pro’s standout advantage is its very large context window, which lets it ingest long documents or many pages at once without chunking. In day-to-day vision tasks the three are close enough that you should test them on your actual images rather than rely on a leaderboard.
Audio and video
This is where the gap widens. Gemini 1.5 Pro can natively process long video and audio because its million-token context can hold an entire video’s frames or a lengthy recording — useful for summarising a meeting recording or analysing a long clip end to end. GPT-4o shines at low-latency, real-time voice conversation and fast audio understanding, making it the better choice for interactive voice experiences. For pure transcription accuracy as a standalone task, a dedicated speech model such as Whisper often still beats a general multimodal model.
Image generation vs image understanding
Do not confuse the two. GPT-4o generates images via DALL-E 3 inside ChatGPT, and Gemini integrates Google’s Imagen for generation. Claude 3.5 reads and analyses images but does not generate them. So if your workflow needs both “describe this chart” and “create a new illustration,” confirm each product’s current output capabilities rather than assuming a model that sees images can also draw them.
How to choose for your task
- Reading documents, charts, and screenshots: Claude 3.5 Sonnet or GPT-4o; Gemini if the documents are very long.
- Long video or long audio analysis: Gemini 1.5 Pro, for its context window.
- Real-time voice interaction: GPT-4o.
- High-accuracy transcription only: a dedicated speech model like Whisper.
- Generating images alongside analysis: GPT-4o (DALL-E 3) or Gemini (Imagen).
The frontier moves fast and product features change between model releases, so validate on your own representative inputs before committing a workflow to one model.