Comparing Reasoning Models

Choosing the right reasoning model

The xAI catalog as of July 2026 includes several models suitable for reasoning: grok-4.5, the three grok-4.20-0309 variants, grok-4.3, and grok-build-0.1 for code. Your choice depends on your use case, budget, and latency constraints. This lesson provides the criteria to make the right decision.

Full comparison table

Prices are listed per million tokens for context under 200k tokens (rates increase beyond this—see lesson 9).

The non-reasoning variant

The grok-4.20-0309 family comes in three variants. It’s important not to confuse them:

• grok-4.20-0309-reasoning: Deep reflection before answering, for complex problems
• grok-4.20-0309-non-reasoning: Direct response without a chain of thought, for simple tasks and minimal latency
• grok-4.20-multi-agent-0309: Orchestrates multiple agents, for distributed architectures

All three share the same 1M token context and the same pricing. The non-reasoning variant isn’t a “discount” model: it’s the right choice whenever the task doesn’t require reasoning (see lesson 12).

Selection criteria

By budget

Input and output pricing follows a clear hierarchy:

1. grok-build-0.1: $1/$2 per MToken—but reserved for code
2. grok-4.20-0309 (all variants) and grok-4.3: $1.25/$2.50 per MToken
3. grok-4.5: $2/$6 per MToken—output costs 2.4x more than on grok-4.20

In all cases, staying under 200k tokens of context avoids the higher pricing tier.

By task complexity

• Simple questions (classification, extraction, rephrasing): grok-4.20-0309-non-reasoning or grok-4.3
• Intermediate problems (text analysis, structured summarization, moderate reasoning): grok-4.20-0309-reasoning, or grok-4.5 with low reasoning effort
• Complex problems (advanced math, multi-step reasoning, critical decisions): grok-4.5 with high effort
• Code (generation, refactoring, quick debugging): grok-build-0.1, the fastest code model in the catalog

By context size

• Up to 500k tokens: grok-4.5 works
• Beyond 500k tokens (entire codebases, document corpora): grok-4.20-0309 or grok-4.3, the only 1M models
• Code up to 256k: grok-build-0.1

By latency constraints

• Fast response required: grok-4.20-0309-non-reasoning, or grok-build-0.1 for code
• Latency acceptable: grok-4.20-0309-reasoning
• No constraints (batch, background tasks): grok-4.5 with high reasoning effort

Decision tree

1. Is the task pure code? Yes → grok-build-0.1
2. Does the task require multi-step reasoning? No → grok-4.20-0309-non-reasoning
3. Does context exceed 500k tokens? Yes → grok-4.20-0309-reasoning
4. Does maximum quality justify $6/M output? Yes → grok-4.5 (high effort)
5. Otherwise → grok-4.20-0309-reasoning

Recommended combinations

In production, you’ll often use multiple models together:

• Triage + processing: grok-4.20-0309-non-reasoning to classify requests, then grok-4.5 for complex requests
• Draft + validation: grok-4.20-0309-reasoning for a first response, grok-4.5 to validate critical cases
• Development + production: Prototype with grok-4.20-0309-reasoning (cost-effective), switch to grok-4.5 for flows where quality matters most
• Agent architecture: grok-4.20-multi-agent-0309 for orchestration, grok-build-0.1 for code subtasks

Prices as of August 5, 2026—pricing changes regularly. Before budgeting, verify the current rates on the official xAI models and pricing page.

Key takeaways

• grok-4.5 is the most powerful reasoning model (configurable), but also the most expensive ($2/$6 per MToken under 200k)
• The three grok-4.20-0309 variants (reasoning, non-reasoning, multi-agent) share 1M context and identical pricing ($1.25/$2.50)
• The non-reasoning variant is the default choice for tasks without reasoning
• grok-build-0.1 is dedicated to code: the fastest and cheapest ($1/$2, 256k context)
• In production, combine models based on each request’s complexity rather than sending everything to the flagship model