AI / Core OpenAI Codex Application Fundamentals Interview Questions
What are reasoning models in the OpenAI API and what is the 'effort' parameter?
Reasoning models (originating with the o1/o3 family and now integrated into the GPT-5.x line) spend additional compute "thinking" through a problem before producing a final answer. This hidden chain-of-thought reasoning dramatically improves performance on complex multi-step tasks like mathematics, coding, and planning.
| Model | Reasoning behaviour |
|---|---|
| gpt-5.5 | Reasoning built-in; effort parameter controls depth |
| gpt-5.4 | Adaptive reasoning - dynamically adjusts thinking time based on task complexity |
| gpt-5.3-codex | Combined frontier coding + strong reasoning in one model |
| gpt-5.4-mini | Faster, lighter reasoning for cost-sensitive tasks |
from openai import OpenAI client = OpenAI() # Responses API with reasoning effort result = client.responses.create( model="gpt-5.5", input="Design a thread-safe cache with LRU eviction in Python.", reasoning={"effort": "high"}, # "low" | "medium" | "high" ) print(result.output_text) # "low" - faster, cheaper; suitable for simple code Q&A # "medium" - balanced; good default for most coding tasks # "high" - maximum reasoning; for complex architecture, hard bugs # Encrypted reasoning (reasoning without exposing thinking tokens): result = client.responses.create( model="gpt-5.5", input="Find all race conditions in this concurrent code: ...", reasoning={"effort": "high", "summary": "auto"}, # get reasoning summary )
Adaptive reasoning in gpt-5.4: this model dynamically adjusts reasoning depth per task. On simple requests it responds quickly (using far fewer tokens); on complex tasks it automatically uses more compute. Testing showed gpt-5.4 uses 93.7% fewer tokens than gpt-5.5 for the bottom 10% of simple user turns, while maintaining full capability on hard tasks.
What does the 'effort' parameter in the Responses API control for reasoning models?
How does gpt-5.4's 'adaptive reasoning' differ from setting a fixed effort level?
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