Fara1.5-4B

Fara1.5-4B is a multimodal computer use agent (CUA) for web browsers, from Microsoft Research AI Frontiers. It observes the browser through screenshots and acts on the user's behalf by emitting structured tool calls — click, type, scroll, visit URL, web search, and so on — to complete tasks end-to-end.

The model is vision-only at perception time: it sees the browser through screenshots, not the DOM or accessibility tree. Internal reasoning and trajectory history are tracked as text. Given the latest screenshot and prior actions, it predicts the next action with grounded arguments (e.g., pixel coordinates for a click).

Fara1.5-4B is supervised fine-tuned from Qwen3.5-4B on data generated by FaraGen1.5, our multi-agent pipeline that synthesizes web tasks, executes trajectories to solve them, and verifies the results before training.

Please use only with the harness developped in Github/fara CLI or Magentic-Lite.

It's co-designed with MagenticLite, and that's the recommended deployment for both research and production.

Highlights

• End-to-end web task completion. Fills forms, books reservations, applies for jobs, plans trips, runs shopping carts. Not just clicking around — sequencing actions toward a goal.
• Vision-only perception. Operates on screenshots alone, no DOM access required. Matches the input modality available to a human user.
• Coordinate-grounded actions. Predicts pixel-level click and drag targets directly. No separate grounding model needed.
• Critical-points safety design. Trained to stop and ask before personal info entry, payments, submissions, sign-ins, sending messages, or other irreversible actions — even if it could technically continue.
• 262K context. Long enough for multi-screenshot trajectories with full action history.
• On-device viable. 4B parameters means it runs on a single A100/H100/B200 with room for the screenshot history.

Model Details

Recommended Deployment: MagenticLite

The safest way to run Fara1.5-4B is inside MagenticLite, which provides:

• Sandboxing — the browser runs in a Docker container with no access to host files or environment variables
• Allow-lists — restrict navigation to a user-specified set of domains
• Watch-mode — real-time monitoring of every action with full trace logs
• Pause — immediate halt of agent activity at any point

If you integrate Fara1.5-4B directly, you're responsible for these controls. Don't run this model with unrestricted browser access on a machine that has anything sensitive on it.

Quickstart

Requirements

• torch >= 2.11.0
• transformers >= 5.2.0
• vllm >= 0.19.1
• A GPU with enough memory for a 4B model in bf16 (A6000, A100, H100, and B200 have been tested)

Serve with vLLM

vllm serve microsoft/Fara1.5-4B \
  --dtype bfloat16 \
  --max-model-len 262144 \
  --limit-mm-per-prompt image=10

System prompt

Fara1.5-4B is trained against a specific system prompt. Use it verbatim for best results:

You are Fara, a computer use agent (CUA) specialized for web browsers. You are developed by Microsoft AI Frontiers. You assist users with completing and automating tasks that require the use of a web browser.

The model was trained in the timeframe of January - April 2026. You can effectively perform tasks even beyond this range by accessing the web browser and using the latest information on the live web. But your knowledge cutoff is limited to early 2026, so you may not be aware of events or developments that occurred after that time, without explicitly browsing and searching for latest information on the web.

This edition of the model was trained using SFT on top of Qwen3.5-4B, using a synthetic data mixture generated and developed by Microsoft AI Frontiers.

A critical point is a situation where we must pause and request information or confirmation from the user before proceeding. There are three types:

Case 1: Missing User Information — The task requires personal information that the user has not provided (e.g., email, phone number, address, payment details). Never fabricate or assume personal information. Fill in only what the user has explicitly provided, then pause and ask for any missing required fields.

Case 2: Underspecified Task — The task description is ambiguous or missing details needed to make a decision at the current step. Pause and ask for clarification.

Case 3: Irreversible Action — We are about to perform an action that cannot be undone (e.g., submitting a form, completing a purchase, sending a message, deleting data). If the user explicitly authorized the action, proceed. Otherwise, stop and ask for confirmation.

Only stop at a critical point if (1) required information is missing, (2) the task is ambiguous, OR (3) an irreversible action lacks explicit user authorization.

The full system prompt, including the complete computer_use tool schema, ships with the model in MagenticLite.

Tool schema

Fara1.5-4B emits actions as <tool_call>...</tool_call> XML blocks containing a JSON object that calls the computer_use function. Supported actions:

The screen resolution Fara is most commonly trained with is 1440×900. Match this in your sandbox for the most reliable grounding.

Minimal agent loop

Note: We strongly recommend to use only with the harness developped in Github/fara or Magentic-Lite.

# Pseudocode for a single-step interaction. Use vLLM's OpenAI-compatible
# endpoint and pass the screenshot as an image content part.

screenshot_b64 = capture_browser_screenshot()  # base64 PNG

messages = [
    {"role": "system", "content": FARA_SYSTEM_PROMPT},
    {"role": "user", "content": [
        {"type": "text", "text": "Book a table for 2 at a sushi place in Sunnyvale for Friday 7pm."},
        {"type": "image_url", "image_url": {"url": f"data:image/png;base64,{screenshot_b64}"}},
    ]},
]

response = client.chat.completions.create(
    model="microsoft/Fara1.5-4B",
    messages=messages,
    temperature=0.0,
    max_tokens=2048,
)

# Parse the assistant's reply: it will contain chain-of-thought text
# followed by <tool_call>{"name": "computer_use", "arguments": {...}}</tool_call>.
# Execute the action in your sandboxed browser, capture the new screenshot,
# append the assistant turn and a tool/observation turn, and loop until
# the model emits action="terminate". We only keep the most recent 3 screenshots
# in the chat history.

A reference implementation of the full agent loop, including screenshot capture and Docker sandboxing, is in MagenticLite.

Critical Points: Safety by Design

Fara1.5-4B is trained to pause and ask the user at three types of critical points:

1. Missing user information. If the task needs personal data (name, email, phone, address, payment) the user hasn't provided, fill in what's available and stop to ask for the rest. Never fabricate.
2. Underspecified tasks. If the goal is ambiguous at the current decision point (e.g., "book me a flight" with no destination), stop and clarify.
3. Irreversible actions. Submitting forms, completing purchases, sending messages, deleting data — stop unless the user explicitly authorized the action upfront.

Concrete actions Fara is trained to stop on without explicit authorization:

• Entering personal information (name, email, phone)
• Entering credit card or shipping/billing details
• Completing purchases or bookings
• Making phone calls
• Sending emails
• Submitting job applications
• Signing into accounts

If the user grants authorization, the model proceeds. The principle is that costly, irreversible actions require a human in the loop.

Evaluation

We evaluate Fara1.5-4B on end-to-end web agent benchmarks. For WebTailBench, we report outcome success.

Training

Approach

Supervised Fine-Tuning on top of Qwen3.5-4B. Training mix is generated by FaraGen1.5, our multi-agent data pipeline, supplemented with curated public datasets for grounding and UI understanding.

Data sources

• Synthetic trajectories — Tasks seeded from URLs sampled from a large web index and from open-source seed datasets (e.g., Mind2Web). A multi-agent system attempts each task while recording screenshots, thoughts, and actions. A verifier agent then keeps only successful trajectories.
• Grounding — Curated datasets for predicting actions and pixel coordinates from screenshots, with images, text, and bounding boxes.
• UI understanding — Visual question answering, captioning, and OCR over web page screenshots collected by the pipeline.
• Safety and instruction following — Refusal data covering harmful or unsafe tasks the model should decline.

Scale

• Approximately 1 billion text tokens
• Less than 1 billion training images
• Latest data acquisition: March 20, 2026
• Training start: January 2026

The corpus is static. Future updates will ship as separately versioned models with their own model cards.

Intended Use and Limitations

Primary use cases

Automating repetitive web tasks: filling forms, shopping, booking travel, restaurant reservations, information seeking, account workflows. Fara1.5-4B can also serve as a grounding model for other agents that need pixel-accurate action prediction.

Out of scope

• Languages other than English (training data is English-only)
• High-stakes domains (legal, health, financial advice) where inaccurate actions could cause harm
• Allocation decisions affecting legal status, housing, employment, or credit
• Unsandboxed deployments with access to sensitive accounts or files
• Commercial or real-world production use without additional testing and safeguards

Known limitations

• Vision-only perception means the model can be misled by deceptive or low-quality page rendering, prompt injections embedded in page content, or visual ambiguity in UI elements
• Multi-step trajectories accumulate error — a misclick early in a sequence can compound
• Run-to-run variance on multi-turn tasks is non-trivial; benchmark numbers are averaged over multiple runs
• The model can hallucinate page state or misattribute information from earlier screenshots

Responsible AI Considerations

Computer use is a powerful capability. An agent that can click, type, and submit in a real browser can also do those things wrong. We strongly recommend:

• Human-in-the-loop monitoring of Fara's actions on the live web with a fast way to halt execution
• Sandboxed execution — run Fara in an isolated container with no access to host files, environment variables, or sensitive credentials
• Allow-listed or block-listed browsing — restrict the agent's reachable surface to limit exposure to malicious pages
• No credential or PII sharing with the agent unless absolutely required and the user has authorized it
• Output verification — Fara can hallucinate, misattribute sources, or be misled by deceptive content; verify before acting on its outputs

Safety evaluation

Fara1.5-4B was evaluated via automated red-teaming on Azure. Coverage included groundedness, jailbreak resistance, harmful content (hate, violence, self-harm), and copyright violations. Safety post-training includes both refusal data for malicious tasks and the critical-points framework described above.

Known model risks

Like all language models, Fara1.5-4B can produce unfair, unreliable, or offensive outputs. Specific concerns:

• Quality of service varies across English dialects and is worse for non-English content
• Representation harms may persist despite safety post-training due to base-model biases
• Information reliability — generated content may be inaccurate or outdated
• Prompt injection — Fara reads page content, and adversarial content on a page may attempt to redirect its behavior

Developers deploying Fara1.5-4B should apply responsible AI best practices and ensure compliance with applicable laws and regulations. Using safety services like Azure AI Content Safety is recommended.

License

Released under the MIT License.

Contact

For information requests under the EU AI Act and related inquiries: MSFTAIActRequest@microsoft.com

Authorized representative: Microsoft Ireland Operations Limited, 70 Sir John Rogerson's Quay, Dublin 2, D02 R296, Ireland.