v3 vs v4: Choosing a Computer Use Model on the API
You want to automate tasks on real desktops and browsers. You could write brittle selectors for UI elements. Or you could let an agent see the screen and act like a human. Coasty's computer use API gives you two CUA versions to choose from. v3 is synchronous and interactive. v4 is autonomous with a pass/fail verifier. Pick the version that matches your needs and budget.
What CUA versions do
- ●cua_version: specify v3 or v4 when you submit a task run.
- ●v3: synchronous loop. You call /v1/runs and poll status until it finishes.
- ●v4: autonomous with a verifier. The agent drives steps until it passes or fails.
- ●Both versions bill $0.05 per agent step.
- ●v4 is ideal for headless tasks that need a clear success criterion.
v3: Interactive, synchronous mode
- ●v3 is meant for developers who want to inspect behavior.
- ●Submit a task with max_steps and deadline_seconds to control execution.
- ●Use GET /v1/runs/{id}/events to stream events like screenshots and actions.
- ●You can cancel or resume a v3 run at any time.
- ●Great for debugging, demos, and workflows where you need visibility.
v4: Autonomous with pass/fail verification
- ●v4 is autonomous. The agent decides steps until it passes or fails.
- ●Provide a system_prompt and an optional instructions field.
- ●The verifier checks results and returns succeeded or failed.
- ●Use on_awaiting_human to pause, fail, or cancel when the agent asks for input.
- ●Best for end-to-end automation that must reach a goal without manual intervention.
POST /v1/runs with cua_version v4
curl -X POST https://coasty.ai/v1/runs \
-H 'Content-Type: application/json' \
-H 'X-API-Key: $COASTY_API_KEY' \
-H 'Idempotency-Key: run-$(date +%s)' \
-d '{
"machine_id": "your-machine-id",
"task": "Open Chrome, navigate to https://example.com and take a screenshot",
"cua_version": "v4",
"system_prompt": "You are a helpful assistant that automates web tasks.",
"max_steps": 10,
"deadline_seconds": 60,
"on_awaiting_human": "pause"
}'
GET /v1/runs to see status
curl -X GET https://coasty.ai/v1/runs \
-H 'X-API-Key: $COASTY_API_KEY'Set cua_version to v4 for autonomous, verifiable tasks. Set it to v3 when you want explicit control and streaming events.
Why computer use beats brittle automation
Traditional automation relies on selectors and fixed APIs. If a UI changes, your script breaks. Computer use agents see the screen and click buttons, type text, and scroll just like a human. They adapt to layout changes and handle dynamic content. This makes them far more robust for real-world tasks like filling forms, navigating complex dashboards, and handling unexpected states.
Choose v3 for interactive debugging and visibility. Choose v4 for fully autonomous tasks that must pass or fail. Build reliable computer use agents with Coasty's API. Get your API key at https://coasty.ai/developers.