How to Use Grok 4.3 API

Released on April 30, 2026, Grok 4.3 represents xAI's latest flagship model, now widely available via the xAI API. It delivers industry-leading performance in non-hallucination rates, agentic tool calling, instruction following, and enterprise domains like case law and corporate finance, all at a fraction of competitor costs.

Priced at $1.25 per million input tokens and $2.50 per million output tokens (The price of CometAPI is Input: $1/M, Output: $2/M), Grok 4.3 undercuts many frontier models by 40-60% while achieving strong benchmark results (e.g., 53 on Artificial Analysis Intelligence Index). It supports a massive 1 million token context window, multimodal inputs (text + image), function calling, structured outputs, and reasoning.

For developers building AI applications — from intelligent agents and RAG systems to coding assistants and enterprise tools — Grok 4.3 offers an unbeatable combination of capability, speed, and economics.

What is Grok 4.3? Key Features

Grok 4.3 is xAI's newest pre-trained flagship model, building on Grok 4.20 with architectural improvements and a December 2025 knowledge cutoff. It emphasizes reasoning-first design, low hallucination, and practical agentic performance.

What is new in Grok 4.3?

The biggest change is not just “another model bump.” xAI’s migration guide says several older models are being deprecated on May 15, 2026, and recommends Grok 4.3 as the replacement for older reasoning and coding models such as grok-4-fast-reasoning, grok-4-0709, grok-code-fast-1, and grok-3. That makes Grok 4.3 the center of the current xAI API strategy.

Grok 4.3 vs. predecessors like Grok 4.20):

• Improved agentic performance and lower hallucination rates.
• Better cost-efficiency on benchmarks (e.g., ~20% lower cost to run full Intelligence Index suite).
• Enhanced tool calling and precise responses.
• Availability across regions (us-east-1, eu-west-1) with high rate limits (1,800 RPM, 10M TPM).

It ranks competitively on leaderboards, often topping agentic and enterprise-specific evaluations while maintaining frontier-level intelligence.

Key features of Grok 4.3

1) Agentic reasoning and tool use

Grok 4.3 around agentic reasoning and tool use. The function-calling show the standard agent loop: define a tool, include it in the request, let the model return a tool_call, execute the function locally, then send the result back so the model can continue. That parallel function calling is enabled by default, so the model can request multiple tool calls in a single response.

2) Large context window

Grok 4.3 a 1 million token context window, which is the kind of scale that matters for long documents, long chat histories, codebases, and multi-file workflows. xAI also calls out special pricing behavior above 200K context, which is useful to mention in a production cost section.

) 3Built-in web search and live data workflows

xAI’s web search tool lets Grok search the web in real time, browse pages, and extract relevant information for up-to-date responses. The docs also say web search is available on the Responses API and that the live-search capability on Chat Completions is deprecated, so the Responses API is the safer long-term choice for new work.

4) Reasoning traces and usage visibility

For Grok 4.3, xAI exposes summarized reasoning content and usage data such as reasoning tokens. That matters for debugging, observability, and cost control. In the docs, xAI shows how to stream reasoning summaries and how to inspect response.usage.output_tokens_details.reasoning_tokens.

Getting Started with Grok 4.3 API: Step-by-Step Setup

1. Create an xAI Account: Sign up at console.x.ai.
2. Generate API Key: Go to API Keys section and create one. Store securely (use environment variables).
3. Choose Access Method:

• Direct xAI API (base URL: https://api.x.ai/v1).
• Recommended: CometAPI for unified access, potential discounts (up to 20% off), free credits on signup, and easier multi-model management.

Why Use CometAPI for Grok 4.3?

• Single API key for 500+ models (including all Grok variants).
• Unified OpenAI-compatible interface.
• Cost savings, usage analytics, and reliability features.
• Free starter credits for new users — perfect for testing Grok 4.3 without upfront commitment.

Visit CometAPI.com to get started with Grok models today.

How to use the Grok 4.3 API

xAI says its API is compatible with OpenAI and Anthropic SDKs, so switching is mostly a matter of creating an API key and changing the base URL. In practice, the cheapest integration path is to use the CometAPI API , then add tools, structured outputs, or streaming as needed.

Step 1: Create an API key

Start by creating a CometAPI account and generating an API key in the console.

Step 2: Choose the model

For most text and reasoning tasks, use grok-4.3. Grok 4.3 strongly recommends this model for API callers, and the overview page lists Grok 4.3 as the model that excels at agentic reasoning, knowledge work, and tool use.

Step 3: Send your first request

The API is OpenAI-compatible, so you can use familiar SDKs.

Python Example (OpenAI SDK)

import os
from openai import OpenAI

client = OpenAI(
    api_key=os.getenv("XAI_API_KEY"),  # or COMETAPI_KEY
    base_url="https://api.x.ai/v1"     # or https://api.cometapi.com/v1 for CometAPI
)

response = client.chat.completions.create(
    model="grok-4.3",  # or grok-4.3-latest
    messages=[
        {"role": "system", "content": "You are Grok, a helpful and maximally truthful AI."},
        {"role": "user", "content": "Explain quantum computing in simple terms with an analogy."}
    ],
    temperature=0.7,
    max_tokens=1000
)

print(response.choices[0].message.content)

Using xAI SDK (Native)

from xai_sdk import Client
from xai_sdk.chat import user, system

client = Client(api_key=os.getenv("XAI_API_KEY"))
chat = client.chat.create(model="grok-4.3")
chat.append(system("You are Grok..."))
chat.append(user("Your prompt here"))
response = chat.sample()
print(response.content)

Image Understanding Example (Vision): Include image URLs in messages for multimodal tasks like document analysis or visual QA.

Structured Outputs & Function Calling

Define tools or JSON schemas for reliable, parseable responses — crucial for agents and integrations.

Streaming Responses for better UX in chat apps. If your app shows live generation, enable streaming. Grok 4.3 sets "stream": true in the request, and reasoning models may need a longer timeout to avoid closing the connection too early.

Prompt Caching: Reuse long contexts (e.g., system prompts or documents) to slash costs dramatically (cached input at $0.20/M).

CometAPI Integration Tip: Swap the base URL and use your CometAPI key for seamless switching between Grok 4.3, other xAI models, or competitors without code changes.

Continue conversations with previous_response_id

xAI’s docs support continuing a session by passing previous_response_id. That is useful when you want memory-like behavior without reconstructing the whole conversation state every time.

first = client.responses.create(    model="grok-4.3",    input=[{"role": "user", "content": "List three use cases for Grok 4.3."}],)followup = client.responses.create(    model="grok-4.3",    previous_response_id=first.id,    input=[{"role": "user", "content": "Turn that into a checklist."}],)print(followup)

Grok 4.3 vs GPT-5.5: which one should you choose?

This comparison is best framed as a product decision, not a winner-take-all benchmark race. Grok 4.3 is xAI’s fastest and most intelligent model for general text workloads, while GPT-5.5 is OpenAI’s newest frontier model for the most complex professional work and supports higher-level reasoning controls.

Comparison Table:

Key Takeaway: Grok 4.3 delivers 80-90% of top-tier performance at 10-20% of the cost, making it ideal for high-volume applications, agents, and enterprises. GPT-5.5 may edge out on certain complex reasoning benchmarks but at a premium price that impacts scalability.

Advanced Features and Best Practices

1) Use the smallest prompt that still preserves the contract

OpenAI’s GPT-5.5 guidance is useful here even when you are building with Grok: start with the smallest prompt that preserves the product contract, then tune the system prompt, tool descriptions, and output format against real examples. That advice applies cleanly to Grok 4.3 too.

2) Set the right reasoning depth

Because Grok 4.3 supports low, medium, and high reasoning effort, do not default every request to maximum depth. Use low reasoning for quick user-facing questions, and reserve higher effort for planning, analysis, or multi-step tool workflows. xAI explicitly recommends low effort for less latency-sensitive workloads.

3) Stream for interactive products

For chat interfaces, live copilots, and customer support tools, streaming improves perceived latency and makes the product feel more responsive. Streaming as especially helpful for real-time feedback.

4) Use cached tokens when prompts repeat

xAI cached input tokens at $0.20 per 1M tokens, which is much cheaper than normal input. That makes a real difference for repeated system prompts, templates, policy blocks, and long instructions that do not change between requests.

5) Add timeouts and retry logic

Reasoning models can take longer than fast chat models. xAI’s own examples set a longer timeout for Grok 4.3, and 3,600-second timeouts in examples where deeper reasoning is expected. Production systems should use retry logic, circuit breakers, and observability around tool calls.

6) Test with real tasks, not toy prompts

A model can look great on a demo and still fail on actual workflows. Evaluate Grok 4.3 against your own inputs: customer tickets, business docs, support transcripts, code review tasks, and agent workflows. That is especially important if you plan to compare it directly with GPT-5.5.

Conclusion: Start Building with Grok 4.3 Today

Grok 4.3 democratizes frontier AI with its performance-to-price ratio, massive context, and developer-friendly API. Whether you're prototyping or scaling production systems, it offers tremendous value.

Recommended Next Step: Sign up at CometAPI.com for instant access to Grok 4.3 (and hundreds of other models) with potential savings and free credits. Generate your key, test the examples above, and unlock powerful AI capabilities without vendor lock-in.