CrewAI Sequential & Hierarchical Process

In CrewAI, a process defines how a crew runs its tasks and coordinates agents, not what the tasks do. Choosing the right process is like choosing a project management style for your AI team.

1. What Is a Process in CrewAI?

A process is the execution strategy that tells a crew in which order and under whose control tasks should run.
Processes make individual agents behave as a cohesive team instead of a collection of isolated workers.
In code, the process is chosen via the Process enum when you create the Crew.

# Python Code
from crewai import Crew, Process

crew = Crew(
    agents=my_agents,
    tasks=my_tasks,
    process=Process.sequential   # or Process.hierarchical
)

2. The Process Enum

CrewAI exposes processes as a type‑safe enum, so you can only pick supported values

Process.sequential
Process.hierarchical
Process.consensual (planned, not yet implemented)

This prevents typos and makes your orchestration behavior explicit and easy to read.

3. Sequential Process

Think of sequential as a classic pipeline.

Tasks run one after another in the order they are listed in the crew.
By default, the output of one task is available as context for the next; you can customize this with each task’s context parameter.
It mirrors many real‑world workflows: research → analyze → write → review.

Example:

crew = Crew(
    agents=my_agents,
    tasks=my_tasks,          # [task1, task2, task3] in order
    process=Process.sequential
)

When to use:

Your process is mostly linear and predictable.
Dependencies are simple: “B should see A’s output, C should see B’s output,” etc.
You are teaching or prototyping and want maximum clarity and debuggability.

4. Hierarchical Process

Think of hierarchical as a manager–worker model.

A manager agent coordinates the work: plans, delegates tasks to other agents, and validates results.
Tasks are not pre‑assigned in a fixed order; the manager decides what to do next and who should do it.
This enables flexible, adaptive workflows for complex projects.

To enable it you must provide either manager_llm or manager_agent:

# Python Code

from crewai import Crew, Process

# Using a manager LLM (CrewAI’s Manager agent is created for you)
crew = Crew(
    agents=my_agents,
    tasks=my_tasks,
    process=Process.hierarchical,
    manager_llm="gpt-4o"
)

# OR: using a custom manager agent you define yourself
crew = Crew(
    agents=my_agents,
    tasks=my_tasks,
    process=Process.hierarchical,
    manager_agent=my_manager_agent
)

How it behaves:

The manager receives the overall objective and current state.
It decomposes the goal into subtasks, assigns them to the best agents, and validates their outputs.
It can loop, re‑assign, or request revisions, just like a human project manager.

When to use:

Complex projects where task order cannot be fully hard‑coded up front.
Scenarios with many specialized agents that must be coordinated dynamically.
You want to mirror organizational structures (PM + specialists, lead dev + engineers, etc.).

5. Consensual Process (Planned)

CrewAI also defines a Consensual process conceptually, but it is planned and not yet implemented.

Idea: agents collectively discuss and agree on which tasks to run and how, using a democratic or voting‑style approach.
Goal: support collaborative decision‑making instead of purely top‑down or strictly linear orchestration.

For now, you should not use this in production code; treat it as a roadmap concept you can mention in your course when discussing future architectures.

6. Choosing the Right Process

Here is a simple decision guide:

Start with Sequential when:

The workflow is a well‑defined pipeline.
You’re learning CrewAI fundamentals (agents, tasks, YAML, crews).

Move to Hierarchical when:

You need a manager agent that can plan, delegate, and validate dynamically.
You want to simulate real teams with leads, reviewers, and specialized workers.

Remember that process selection = collaboration pattern: it’s not about what each agent knows, but how the team decides who does what, when, and in which order