AI Models
VibeRails supports multiple AI models across two CLI backends. Choose the right model for your review based on depth, speed, and cost requirements.
Overview
VibeRails does not call AI APIs directly. Instead, it orchestrates local CLI tools — Claude Code and Codex CLI — which handle authentication and model access. You select a CLI backend and model in the review wizard (step 2) or fix session wizard (step 3).
Claude Code Models
When you select Claude Code as the CLI backend, the following models are available:
| Model | Strengths | Speed | Extended Thinking |
|---|---|---|---|
| Opus 4.5 | Deepest analysis, best at finding subtle bugs and security issues. Strongest reasoning across all categories. | Slowest | Available |
| Sonnet 4 | Excellent balance of quality and speed. The recommended default for most reviews. | Fast | Available |
| Haiku | Fastest and most cost-effective. Good for quick scans and initial passes on large codebases. | Fastest | Not available |
Extended Thinking
Opus 4.5 and Sonnet 4 support Extended Thinking, which gives the model additional time to reason through complex problems before responding. When enabled, the model produces more thorough analysis at the cost of longer review times.
Extended Thinking is especially valuable for:
- Security audits where subtle vulnerabilities require multi-step reasoning
- Complex concurrency or state-management code
- Large files with interrelated logic across many functions
Codex CLI Models
When you select Codex CLI as the backend, the following OpenAI models are available:
| Model | Strengths | Speed | Reasoning Level |
|---|---|---|---|
| O3 | Most capable OpenAI reasoning model. Excels at complex logic, mathematical reasoning, and nuanced code analysis. | Slowest | Low / Medium / High |
| O3-mini | Balanced reasoning model. Good quality with faster throughput than full O3. | Medium | Low / Medium / High |
| O4-mini | Latest compact reasoning model. Fast and cost-effective with strong code understanding. | Fast | Low / Medium / High |
Reasoning Levels
All Codex CLI models support configurable Reasoning Levels that control how much compute the model spends thinking before responding:
| Level | Behaviour | Best For |
|---|---|---|
| Low | Minimal reasoning. Fast responses with basic analysis. | Quick scans, style checks, obvious bugs. |
| Medium | Moderate reasoning. Balanced depth and speed. | General-purpose reviews. The recommended default. |
| High | Maximum reasoning. Deepest analysis with longest response time. | Security audits, complex algorithm review, critical-path code. |
When to Use Which Model
The right model depends on your priorities. Here is a decision guide:
| Scenario | Recommended Model | Settings |
|---|---|---|
| Everyday code review | Sonnet 4 | No extended thinking |
| Quick scan of a large codebase | Haiku or O4-mini | Low reasoning |
| Security audit | Opus 4.5 or O3 | Extended thinking / High reasoning |
| Pre-release review | Sonnet 4 or O3-mini | Extended thinking / Medium reasoning |
| Fix session (generating patches) | Sonnet 4 or O4-mini | Default settings |
| Cost-sensitive / high-volume | Haiku or O4-mini | Low reasoning |
Configuration in Wizards
You select the AI model at two points in the VibeRails workflow:
Review Wizard (Step 2)
When creating a new code review, step 2 of the wizard lets you pick the CLI backend, model, and thinking/reasoning options. Your selection is saved with the review so you can compare results across different models.
Fix Session Wizard (Step 3)
Fix sessions also let you choose a model. You may want a different model for fixes than for reviews — for example, using Sonnet 4 for review but Haiku for generating quick patches.