This is Hamamoto from TIMEWELL.
OpenAI DevDay 2025 marked a historic turning point for developers.
The Apps SDK transformed ChatGPT into an "app hub," enabling integrations with Coursera, Booking.com, Spotify, and other external services. Agent Kit lets you design workflows without writing code, with Human-in-the-Loop easily built in. Codex reaching General Availability (GA) enabled Slack integration, and the GPT-5 Pro API and Sora 2 API were opened to developers.
This article covers every DevDay 2025 announcement and the state of adoption as of early 2026.
OpenAI DevDay 2025: Announcements at a Glance
| Item | Details |
|---|---|
| Apps SDK | Integrate external apps directly into ChatGPT |
| Agent Kit | Build agents without code |
| Agent Builder | Design workflows with a block diagram |
| Chat Kit | Chat UI component library |
| Codex GA | General availability; Slack integration |
| Codex SDK | TypeScript support |
| GPT-5 Pro API | Top-tier model API access opened |
| Sora 2 API | Video generation API opened |
Apps SDK — ChatGPT Becomes an App Hub
External App Integration
Apps SDK is a developer kit for embedding external apps directly into ChatGPT's conversation space.
Apps SDK Features:
- Access app functionality while preserving conversational context
- Internally leverages the MCP protocol
- Interactive in-conversation operations
- Optimized for chat-first experiences
Integration Partners
Key partners announced at DevDay 2025:
| Category | Service |
|---|---|
| Learning | Coursera |
| Travel | Booking.com, Expedia |
| Music | Spotify |
| Business | Various SaaS tools |
Example Use Cases
Coursera Integration:
- Play lecture videos directly within ChatGPT
- Ask questions about confusing content on the spot
- Receive explanations aligned with the current slide
- No interruption to the learning flow
Travel Booking:
- "Find a hotel in San Francisco under $300 per night"
- Candidates appear within the chat interface
- Navigate to the booking page with a button tap
Developer Guidelines
Apps SDK provides "patterns" for interaction design.
Design Principles:
- Prioritize key points over long text
- Favor UI that leads to action
- Mutual reinforcement between conversation and operation
Agent Kit — No-Code Agent Building
Agent Builder
Agent Builder is a tool for designing AI agent workflows using block diagrams.
Agent Builder Features:
- Accept text input
- Select model and set reasoning intensity
- Configure conditional branching
- Define tool integrations
- Visual workflow design
Features Showcased in Demo:
- Template "Planning Helper"
- Real-time preview on the right side
- Instant verification of each node's behavior
Human-in-the-Loop
A key capability of Agent Kit is "User Approval."
Human-in-the-Loop Features:
- Embed human review and approval steps in workflows
- Ideal for quality- and safety-focused operations
- Use for legal review, brand approval, and final sign-off on customer interactions
RAG Functionality
Agent Kit comes with built-in RAG (Retrieval-Augmented Generation).
RAG Features:
- Upload documents to Vector Store
- Use user questions as queries for search
- Generate answers while referencing the most relevant documents
- Integration with internal documents and FAQs
Evaluation and Operations
Evaluation Dashboard:
- Review execution logs
- Understand user reactions
- Promote improvement cycles
Publishing:
- Issue agent IDs
- Embed into front-end interfaces
- End-to-end development flow is in place
Chat Kit
Chat Kit is a component library for building chat UIs.
Chat Kit Features:
- Import pre-built components
- Implement chat UI with minimal code
- Integrate with agents built in Agent Builder
- Focus on building the agent's core logic
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Codex GA — General Availability
Slack Integration
Codex has reached General Availability (GA).
Slack Integration Features:
- Simply mention "@codex" to trigger it
- Task processing informed by conversation context
- Runs in a cloud-based execution environment
- Automates script creation and preparatory work
Use Cases:
- Convert even informal, conversational instructions into tasks
- Usable by business teams, not just developers
- The feeling of "assigning work to AI"
Terminal and CLI Integration
Developer-Facing Features:
- Integration with terminal operations
- CLI (command-line interface) support
- Natural integration into everyday development tools
Codex SDK
The Codex SDK makes it easy to embed agent functionality into applications.
Codex SDK (TypeScript Support):
- Embed agent functionality in a few lines of code
- Integrate into products and internal tools
- Works with Agent Kit and Chat Kit
End-to-End Development Experience:
- Create workflow with Agent Kit
- Build UI with Chat Kit
- Call processing with Codex SDK
GPT-5 Pro API
Top-Tier Model Access
GPT-5 Pro is now available as a developer API.
GPT-5 Pro API Features:
- Programmatic access to the top-tier model
- Ideal for spot use where accuracy matters most
- Higher pricing
- "Use the best model just here" for demanding scenarios
Recommended Use Cases
- High-accuracy judgment and analysis
- Output for important customer-facing content
- Scenarios where quality is the top priority
Sora 2 API
Video Generation API Access
Sora 2 is now accessible via API.
Sora 2 API Features:
- High-quality output support
- Larger output sizes
- Per-second billing
- Not inexpensive
Generation Time:
- May be longer in current state
- Batch processing and job management strategies required
Recommended Use Cases
- Short, high-quality advertisements
- Teaser clips
- High-value content production
The Significance of DevDay 2025
ChatGPT's Evolution
DevDay 2025's message was clear.
ChatGPT's New Positioning:
- Not just a conversational engine
- The front door to applications
- The driver's seat for agents
- An integrated platform connected to development execution environments
Unified Development Experience
End-to-End Flow:
- Apps SDK: Pathways from conversation to action
- Agent Kit: No-code design
- Codex and various APIs: Operational deployment
What It Means for Enterprises
Key Shifts:
- Shorter distance from prototype to production
- AI as a "shared work partner" across departments
- AI adoption barriers are definitively lower
Then vs. Now: Evolution Since DevDay 2025
| Item | Then (May 2025, DevDay Announcement) | Now (January 2026) |
|---|---|---|
| Apps SDK | Announced, limited release | Partner expansion, full rollout |
| Agent Kit | Beta | Stable version, enhanced evaluation |
| Chat Kit | Initial version | Component library expanded |
| Codex | GA launched | Slack integration established, use cases growing |
| Codex SDK | TypeScript only | Multi-language support under consideration |
| GPT-5 Pro API | Limited access | Expanded to general developers |
| Sora 2 API | Announced | Commercial use cases increasing |
| Ecosystem | Being built | Moving toward maturity |
Competitor Comparison
OpenAI vs Anthropic
| Item | OpenAI | Anthropic |
|---|---|---|
| Agent Tools | Agent Kit (no-code) | Claude Code (code-centric) |
| App Integration | Apps SDK | MCP |
| Developer Experience | Integrated platform | API-centric |
| Video Generation | Sora 2 | None |
OpenAI vs Google
| Item | OpenAI | |
|---|---|---|
| Agents | Agent Kit | Vertex AI Agent Builder |
| No-Code | Agent Builder | Firebase Studio |
| Search Integration | ChatGPT Search | AI Overview |
| Video Generation | Sora 2 | Veo 3 |
Actions for Developers
Short-Term (~3 Months)
1. Evaluate Agent Kit
- Prototype using templates
- Consider application to your own operations
2. Deploy Codex Slack Integration
- Pilot within the team
- Measure effectiveness
Mid-Term (3–6 Months)
1. Adopt Apps SDK
- Explore integration with your own services
- Design user experience
2. Deploy to Production
- Publish agents built with Agent Kit
- Build operational framework
Long-Term (6+ Months)
1. Join the Ecosystem
- Roll out as an Apps SDK partner
- Offer proprietary agents
2. Continuous Improvement
- Improve quality using evaluation features
- Incorporate user feedback
Summary
OpenAI DevDay 2025 marked the turning point where ChatGPT evolved from a "conversational engine" to an "integrated platform."
Key Points:
- Apps SDK makes ChatGPT an app hub, with Coursera, Booking.com, and Spotify integrated
- Agent Kit enables no-code agent building with Human-in-the-Loop support
- Agent Builder for block-diagram workflow design; Chat Kit for UI construction
- Codex GA with Slack integration; ask @codex to handle tasks
- Codex SDK (TypeScript) for embedding agent functionality in apps
- GPT-5 Pro API for programmatic access to the top-tier model
- Sora 2 API for video generation with high-quality, large output
- The "gap" from prototype to production has narrowed
About eight months since the May 2025 DevDay announcement — the features released are steadily maturing and the developer ecosystem continues to expand. With conversation, UI, workflow, and execution infrastructure aligned in a single stack, the barriers to AI adoption are definitively lower.
Going forward, the differentiator will be practical design decisions: which workflows to start with, which knowledge to use as a foundation, and where to insert human approval. Building small, iterating fast, learning from evaluation, and applying it to the next cycle — that kind of execution will deliver results more directly than ever.
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