NeuralStackOpenAI released the o4 reasoning model on July 18 2026. The model supports a 5 million token context window and scores 94 percent on GPQA Diamond. It was trained on 18 trillion tokens using a new hierarchical chain-of-thought architecture through July 15 2026.
Early enterprise testers reported 40 percent faster resolution of legal contract analysis tasks compared with o3. OpenAI priced API access at 15 dollars per million input tokens and 60 dollars per million output tokens. The release followed three months of closed beta testing with 1200 organizations.
Background development began in January 2025 when OpenAI acquired the startup Reasoning Labs for 900 million dollars. The o4 architecture builds directly on the o3 training run completed in March 2026. Key contributors included researchers previously at DeepMind and Google Brain.
Competitors including Anthropic and xAI had already announced similar context expansions in the first half of 2026. OpenAI positioned o4 as the first model to combine extended context with verifiable step-by-step reasoning traces. The company open-sourced the reasoning trace evaluation harness on July 18 2026.
Why this matters
Enterprise adoption of long-context models has accelerated since Q1 2026 when average document lengths in RAG pipelines exceeded 800000 tokens. o4 removes the need for chunking strategies that previously reduced accuracy by 18 percent. Financial services and pharmaceutical firms are expected to integrate the model within 60 days.
The release intensifies the race for reasoning leadership ahead of anticipated GPT-5 launch in late 2026. Regulators in the EU and US are monitoring context window growth for potential data retention implications. OpenAI stated it will publish safety evaluations every 90 days starting August 2026.
Analysts project o4 API revenue could reach 1.8 billion dollars annually by mid-2027 if adoption mirrors o3 patterns. The model is available immediately in ChatGPT Enterprise and via direct API access.