Claude Projects launched in late 2025 and quickly became the core reason many professional users switched from ChatGPT to Claude.

It's not just "conversation categorization"—it's a complete context management system.

1. Core Differences: Projects vs. Regular Conversations

Regular conversations: Each conversation is independent; Claude remembers nothing. Projects: Persistent context; every conversation carries the project background.

In Projects, you can:

Upload up to 20 files as a knowledge base

Set system-level instructions (Project Instructions)

All conversations share the same project context

Conversation history is visible within the project

2. The Art of Project Instructions

Project Instructions act as Claude's "work manual." Writing them well is key.

2.1 Golden Structure

Role Definition
You are [Role] at [Company], responsible for [Responsibilities].
Background Knowledge
[Core background of company/product/project, 300 words max]
Working Rules
[Specific rule 1]
[Specific rule 2]
[Specific rule 3]
Output Requirements
Format: [Your preferred format]
Tone: [Professional/Friendly/Concise]
Length: [Expected answer length]

2.2 Real Example: Product Manager's Project

Role
You are my product design assistant, helping analyze user needs, write PRDs, and design feature solutions.
Product Background
I'm building an AI customer service SaaS product for SMBs.
Current stage: 200 paying customers, 5,000 MAU, ~$1.2M ARR.
Main competitors: Intercom, Zendesk. Our differentiators: better Chinese AI capabilities and lower pricing.
User Persona
Primary decision-makers: IT managers or operations directors at SMBs.
Core pain points: high customer service labor costs, slow response times, no overnight coverage.
Working Rules
Feature suggestions must consider impact on existing customers.
Prioritize using the ICE framework (Impact × Confidence × Ease).
Technical solutions must account for our 3-person engineering team.
Competitive analysis should pay special attention to Intercom's approach.
Output Requirements
PRDs in standard format (Background → Goals → User Stories → Feature Details → Acceptance Criteria).
Clearly list trade-offs when evaluating solutions.

3. Best Practices for File Uploads

Projects supports uploading PDF, Word, TXT, code files, etc.

3.1 Which Files Are Worth Uploading

Highly recommended:

Company/product introduction documents (give Claude context)

Team standards/code style guides

Competitive analysis reports

Industry terminology glossaries

Not recommended:

Large documents over 100 pages (Claude can't fully process them)

Frequently updated content (must re-upload after updates)

3.2 Tips for Optimizing How Claude Understands Files

After uploading, tell Claude how to use the file:

"I've uploaded our company product manual. From now on, when you need details about our product's features,
please refer to this manual first, rather than making assumptions based on your general knowledge.
If the manual doesn't cover something, please state that clearly."

4. Cross-Conversation Workflow Design

4.1 Project Structure: Planning → Execution → Review

Planning phase:

Conversation 1: Upload background materials + discuss solutions
Conversation 2: Refine technical solutions
Conversation 3: Generate execution plan

Execution phase (one conversation per small task):

Benefit: Each conversation focuses on a single task, keeping context clearer.

Upload phase outputs as files for reference in subsequent conversations.

4.2 Create Multiple Sub-Projects for the Same Project

For complex projects, create multiple Projects:

"XX Project - Technical Solution" (upload architecture docs)

"XX Project - User Research" (upload interview transcripts)

"XX Project - Market Analysis" (upload competitive reports)

5. Integration with API (Advanced Usage)

If you call Claude via API, you can simulate Projects in the system message:

python
import anthropic
client = anthropic.Anthropic()
Simulate Project Instructions
project_instructions = """
You are a customer service assistant at [Company], handling product-related issues.
[Detailed background and rules]
"""
Load knowledge file content
with open("product_manual.txt") as f:
    knowledge = f.read()
system_message = f"{project_instructions}\n\nProduct Manual:\n{knowledge}"
message = client.messages.create(
    model="claude-sonnet-4-5",
    max_tokens=2048,
    system=system_message,
    messages=[{"role": "user", "content": "User question"}]
)

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Further Reading

Claude Sonnet 4.5 Complete Guide

ChatGPT Advanced Features Complete Guide

AI Agent Prompt Engineering in Practice