Anthropic announces "Built with Claude 4.5" challenge for developers (support.claude.com)

Anthropic launched the “Built with Claude 4.5” developer challenge running Sept. 30–Oct. 7, 2025, inviting devs to post a short project demo on X (by reposting the original @alexalbert__ announcement with comments) or in Anthropic’s “Claude Developers” Discord #share-your-project channel. Entries must show something built in a week or less, include screenshots/demos, explain what was built and how, and describe how Claude Sonnet 4.5 and its features were used. Anthropic will pick four winners by Oct. 10 based on engagement and originality; each winner receives one year of Claude Max 20X access (approx. $2,400) plus $1,000 in API credits. Multiple entries are allowed but a person can win only once per year; employees and residents outside a specified list of countries are ineligible, and standard contest/legal restrictions apply. For the AI/ML community the contest is a targeted push to surface rapid-prototype use cases of Sonnet 4.5 and drive hands-on experimentation with Anthropic’s latest model features. The one-week constraint encourages minimal viable products, creative prompt engineering, and demos that showcase specific Claude capabilities, while the Max 20X and API credits lower friction for follow-up development. Technical and ethical guardrails are notable: entries can’t aim to reverse-engineer third-party systems or violate Anthropic’s ToS, and the contest includes strict liability and jurisdiction clauses that may affect prize delivery in some regions.