The term "AI coding assistant" covers two very different tools. One predicts the next few lines as you type. The other takes a high-level goal, plans a sequence of steps, and edits files on your behalf. Understanding the difference is the first step to using either well.
Inline Completion: Faster Typing
Inline completion, like GitHub Copilot or Cursor's tab suggestions, watches your cursor and suggests the next line, function, or block. The model sees your current file and maybe a few related files. It predicts what you would type next.
The value is speed. A good suggestion saves you from typing boilerplate, remembers API names, and fills in patterns you have already established. The limitation is scope. The tool does not plan. It reacts to what you are doing right now.
Inline completion works best when you know exactly what you are building and just need help expressing it. It is less helpful when you are exploring an unfamiliar problem.
Agentic Coding: Delegated Tasks
Agentic coding, like OpenCode or Claude Code, takes a natural language goal and breaks it into steps. It reads files, writes changes, runs commands, and checks results. You approve the plan and review the diff.
The value is delegation. You can ask for a refactor across multiple files, and the agent handles the mechanical work. The limitation is supervision. The agent can misunderstand the goal, miss important files, or introduce subtle bugs. You still need to review everything.
When to Use Which
Use inline completion when:
- You are writing familiar code
- The task fits in one function or file
- You want to stay in the flow of typing
Use agentic coding when:
- The task touches multiple files
- You need to run tests or commands as part of the task
- You want to describe the outcome, not the keystrokes
Many developers use both. Cursor, for example, combines inline completion with an agent mode. OpenCode focuses entirely on the agent side.
Agentic coding is not autopilot. The agent needs clear instructions, relevant context, and human review. The more ambiguous the task, the more likely the agent is to go off track.
The Spectrum, Not a Binary
In practice, the two modes blur. An agent can suggest inline-style completions. An inline completion tool can chain a few commands. The useful distinction is who is driving. Inline completion augments your typing. Agentic coding augments your planning and execution.
Choosing the right mode for the task is what separates productive use from frustration.
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