xAI releases Grok 4.20 with 2M context window and native reasoning capabilities

xAI Releases Grok 4.20 With 2M Context and Reasoning Mode

xAI released Grok 4.20 on March 31, 2026. The model features a 2 million token context window, priced at $2 per million input tokens and $6 per million output tokens. Web search functionality costs $5 per 1,000 queries. Knowledge cutoff is September 1, 2025.

Key Specifications

Context and Pricing:

• Context window: 2,000,000 tokens
• Input pricing: $2/M tokens
• Output pricing: $6/M tokens
• Web search: $5 per 1,000 queries

Capabilities: Grok 4.20 includes native agentic tool-calling abilities and an optional reasoning mode that can be enabled or disabled via API parameter. When enabled, the model exposes its step-by-step reasoning process through a reasoning_details array in the response. Users can preserve reasoning context across multi-turn conversations by passing the complete reasoning details back in subsequent requests.

Performance Claims

xAI claims Grok 4.20 delivers "industry-leading speed" combined with low hallucination rates and "strict prompt adherence." The company positions the model as producing "consistently precise and truthful responses," though specific benchmark scores against competing models have not been disclosed.

Technical Details

The model is accessible through OpenRouter, which normalizes API requests and responses across multiple providers and includes fallback routing to maximize uptime. OpenRouter's documentation indicates support for reasoning-enabled models with access to internal step-by-step thinking before final outputs.

API integration follows standard patterns with optional OpenRouter-specific headers for leaderboard attribution. Third-party SDK support is available through OpenRouter's framework documentation.

What This Means

Grok 4.20 enters a competitive market where context window size has become a commodity feature—Claude 3.5 Sonnet and other models already offer 200K context, and some specialty models exceed 1M. The 2M window is a notable advantage but not unprecedented. The model's value proposition rests on claimed speed advantages and agentic capabilities rather than raw context size alone. The optional reasoning mode, similar to features in newer OpenAI and Anthropic models, allows developers to choose between faster inference and detailed reasoning transparency based on use case requirements. Pricing at $2/$6 positions it at the premium end of the market—significantly higher than open-source alternatives but within range of other flagship models. The lack of disclosed benchmark scores leaves performance claims unverified; independent evaluation will be necessary to validate xAI's claims about hallucination rates and prompt adherence relative to competitors.