GPT-5 Codex vs Horizon Alpha: side-by-side summary

GPT-5 Codex and Horizon Alpha are available through the OpenRouter API, so switching between them takes a model slug change rather than a new integration.

GPT-5 Codex, from OpenAI, has a 400,000-token context window and is priced by the provider serving it on OpenRouter.

Horizon Alpha, from OpenRouter, has a 256,000-token context window and is priced by the provider serving it on OpenRouter.

Context window

• GPT-5 Codex: 400,000 tokens
• Horizon Alpha: 256,000 tokens

Price

• GPT-5 Codex: Pricing varies by provider
• Horizon Alpha: Pricing varies by provider

Provided by

• GPT-5 Codex: OpenAI
• Horizon Alpha: OpenRouter

• GPT-5 Codex model details, providers and pricing
• Horizon Alpha model details, providers and pricing