Y Combinator

The Winter 2025 application deadline is in less than a week! Apply at ycombinator.com/apply.

Y Combinator is accepting applications for its Winter 2025 batch by November 12th as it transitions to a four-batch annual schedule to capitalize on a unique twenty-year cycle of technological advancement. The program specifically targets early-stage technical teams with co-founders, emphasizing that hesitation is unnecessary given the organization's history of radically altering founders' trajectories even when applications began on a whim. By encouraging ambitious applicants to submit proposals immediately, YC asserts that the selection process offers a risk-free opportunity to fundamentally reshape the future course of their ventures.

The 10 Trillion Parameter AI Model With 300 IQ

Leslie Kendrick, Mark Mandelmann, Jared, Harj, Paul Lewis O'

OpenAI recently secured a historic $6.6 billion funding round to accelerate the development of 10 trillion parameter models that promise to match human genius-level intelligence in scientific discovery and software engineering. While the O1 model achieves near-perfect accuracy for knowledge worker tasks, market dynamics are shifting as competitors like Claude and Llama gain significant developer share and startups rapidly adopt agentic coding tools like Cursor. This capital-intensive scaling strategy aims to overcome current latency and cost barriers, potentially transforming enterprise operations by replacing legacy systems with autonomous AI workflows.

You Don’t Have To Be A Billionaire To Launch Satellites

John Gedmark, Ryan MckLinko, Jason Carman

Eight years after transforming from a two-person apartment startup into a multi-billion dollar entity, Astronis became the first Y Combinator-backed company to successfully launch a commercial satellite into space. The firm, founded by John and Ryan, disrupted the $122 billion geostationary orbit market by securing a dedicated Falcon 9 launch for four low-cost satellites while internalizing critical manufacturing and testing processes at their Pier 70 facility. This historic achievement validates a strategy where scrappy engineering and a working prototype overcame traditional funding barriers, proving that regular domain experts can build successful hard tech aerospace companies without billionaire backing.

Why OpenAI's o1 Is A Huge Deal | YC Decoded

OpenAI has released the O1 Preview and O1 Mini models, a new class of systems designed for advanced reasoning that match PhD-level performance on complex scientific and coding benchmarks through self-generated chain-of-thought processes. Unlike previous architectures requiring manual prompt engineering, these models utilize large-scale reinforcement learning to decompose problems into verifiable steps, with accuracy improving dynamically as they allocate more "thinking time" to correct errors. While early testing shows mixed preference over GPT-4o for creative tasks, Sam Altman characterizes the technology as a foundational leap comparable to the GPT-2 stage, promising rapid evolution toward GPT-4 capabilities and future multi-modal integration within months.

Starting A Company? The Key Terms You Should Know | Startup School

Dalton Caldwell

This session defines critical startup financial mechanics, including burn rate, profitability thresholds, and the structural differences between angel, seed, and Series A funding rounds. It distinguishes between equity instruments like convertible notes and SAFEs while explaining how metrics such as ARR and Total Addressable Market inform valuation and growth strategy. The discussion concludes by outlining the transition from finding product-market fit to scaling operations, ultimately leading toward an IPO or sustained bootstrapping.

Now Anyone Can Code: How AI Agents Can Build Your Whole App

Amjad Masad, Jared Harge, Diana, Mark Mandelmann, Zahid Ali Jeelani, Francesc Campoy Flores, Franc Espinosa, Mark Manderson, Mark Mandelbacher, Mark Mandalbach, Amjad Ali Khani

Replit has unveiled the Replit Agent, a multi-system that builds full-stack web applications from natural language prompts using a specialized orchestration of Claude Sonnet 3.5 and GPT-4.0 models. This early-access beta enables rapid development of complex projects like mood tracking dashboards while co-founder Amjad Ali frames the technology as a step toward AGI that necessitates a symbiotic human-AI workflow. Future iterations aim to expand stack agnosticism and visual interaction modes while maintaining the tool within Replit Core subscriptions to manage significant computational costs.

Why Design Matters: Lessons from Stripe, Lyft and Airbnb

Katie Dill

Stripe Head of Design Katie Dill explains how the company unifies its creative functions to embed design directly within product squads, prioritizing intentional craft over speed to build the high level of trust required for financial transactions. By implementing rigorous quality frameworks like "Our Essential Journeys" and a "pre-flight" mindset for flaw detection, Stripe has successfully launched tools like Workbench that eliminate developer context switching while driving significant conversion gains through refined user interfaces. Dill emphasizes that founders must cultivate taste and defer to design expertise, as the resulting utility and beauty are fundamental drivers of long-term product value rather than superficial enhancements.

How Do Billion Dollar Startups Start?

This presentation challenges the myth of immediate startup success by highlighting how companies like Airbnb and Solugen evolved through pivots, garage origins, and intense founder commitment rather than initial perfection. Speakers emphasize that YC investors prioritize traits such as grit, bias for action, and transparent communication over polished products or perfect financials. Ultimately, the discussion argues that building billion-dollar enterprises requires an outlier mindset where founders embrace uncertainty and iterate relentlessly to find product-market fit.

The best consumer companies incorporate both virality and network effect to grow organically.

Metcalfe's Law posits that a network's value scales with the square of its user base, transforming a single-user platform like WhatsApp from worthless to globally vital. This dynamic illustrates how the mathematical relationship between nodes and utility drives exponential growth for individual participants. Consequently, consumer companies achieve organic expansion by strategically combining distinct mechanisms of virality and network effects.

Why Vertical LLM Agents Are The New $1 Billion SaaS Opportunities

Jake Heller, Gary, Jared

Following the release of GPT-4, Case Text executed a rapid strategic pivot directed by founder Jake Heller to develop Co-Counsel, a vertical AI agent that achieved a $650 million acquisition by Thomson Reuters after accelerating valuation from $100 million to exit level in just two months. The company secured this market dominance by implementing a rigorous test-driven development methodology that eliminated hallucinations in mission-critical legal tasks, reducing complex document review workflows from days to mere seconds while outperforming previous models on legal benchmarks. This fundamental shift from incremental automation to reliable, system-thinking agents demonstrates how deep domain integration and founder-mode execution can transform speculative AI concepts into essential infrastructure for the legal industry.

Stripe Head of Design Katie Dill Reviews Startup Websites

Katie Dill, Aaron Epstein

This session establishes core web design principles prioritizing immediate value clarity and mobile responsiveness while critiquing six specific healthcare and B2B technology sites. Reviewers identified critical usability failures across these platforms, including excessive scrolling on Mito Health, visual clutter on Cygnaz, and confusing brand identity on Taiv, which collectively risk user abandonment. The discussion concludes with actionable recommendations to align visual hierarchy, consistent typography, and clear calls-to-action with user scanning behaviors to boost trust and conversion rates.

How To Find A Co-Founder | Startup School

Harj Taggar

The event outlines a comprehensive strategy for startup founders to secure co-founders who can double execution capacity, enhance quality control, and provide essential emotional resilience. It emphasizes selecting partners based on stress tolerance and aligned goals rather than specific technical skills, recommending equal equity splits and a trial period to mitigate the risks of role disputes or work ethic mismatches. By leveraging networks for organic connections and maintaining regular communication, founders can avoid common breakup causes and build a durable team capable of competing with established entities.

Once you identify the problem and fix it, you can always launch again.

Founders encountering zero user adoption are advised to replace emotional reactions with a diagnostic, analytical mindset that treats the stagnation as a solvable problem. By systematically iterating on single variables each week, such as refining email copy or pivoting from large enterprise targets to smaller organizations, leaders can isolate specific drop-off points like low reply rates. This structured approach enables the identification of root causes and facilitates targeted adjustments to drive eventual growth.

Building The World's Best Image Diffusion Model

Suhail Doshi, Garry

Playground Labs founder Suhail Doshi launched "Soda," a novel image generation model built from scratch with an 8,000-token context window to enable precise commercial design control. The platform strategically pivots toward professional utility by replacing text-first interfaces with a visual workflow that targets the $2.3 billion Canva market while avoiding the "toy" segmentation of consumer tools. Backed by Doshi's previous SaaS and browser experiences, the hybrid startup combines rapid commercial shipping with dedicated research to refine spatial reasoning and text accuracy for non-designers.

Signs Your Company Is Recovering From ZIRP

Dalton, Michael

Hosts define the current economic recovery from the "Zerp" era as a period marked by the elimination of vanity projects, the removal of excessive perks, and a mandatory return to office to enforce a culture of accountability. This shift involves high executive turnover and founders reclaiming operational control to replace ineffective leadership with a wartime mentality that prioritizes substantive output over comfort. The speakers advise employees to adapt to increased work intensity and stricter standards, warning that those remaining in stagnant organizations should consider leaving to join entities genuinely correcting their strategic errors.