Jobs in United States

Ai Systems Engineer in United States

5,082 active opportunities · Updated October 2026

Explore current ai systems engineer jobs across United States. Filter by work mode, employment type, experience, department, date posted and distance.

F
📍 San Francisco, California, United States· Full-time
✓ High-confidence listingCompany trend -85.5%

From $196.9K/yr

Quick readStrong listing-quality and freshness signals

About Flexport: At Flexport, we believe global trade can move the human race forward. That’s why it’s our mission to make global commerce so easy there will be more of it. We’re shaping the future of a $10T industry with solutions powered by innovative technology and exceptional people. Today, companies of all sizes—from emerging brands to Fortune 500s—use Flexport technology to move more than $19B of merchandise across 112 countries a year. The recent global supply chain crisis has put Flexport center stage as we continue to play a pivotal role in how goods move around the world. We are proud to have the support of the best investors in the game who believe in our mission, solutions and people. Ready to tackle global challenges that impact business, society, and the environment? Come join us. The opportunity The Autonomous Freight Systems team is a brand new, AI-first engineering team in San Francisco. This team will own Flexport’s client-facing rates platform and the self-serve freight booking experience—two of the highest-leverage surfaces in our Client App that dictate how clients see pricing and book freight without manual intervention. As a Staff Engineer, you will be the technical anchor for our next-generation AI-powered rates platform. We aren't just building a UI; we are building AI agents that handle real logistics work: parsing complex rate sheets, managing pricing intelligence across ocean, air, and trucking, and making "Self-Serve" a reality for thousands of shippers. You will build the intelligence layer that allows clients to commit freight on technology alone, with no account executive and no operations touch. This is a ground-floor opportunity to shape technical direction, set up a new codebase, and build the platform that moves Flexport from an assisted-sales model to a tech-run one for the long tail of our client base. You will partner with Pricing, Sales, Ops, and Design on hard domain problems and ship to the most-used client

JavaReactAWSAI
R
📍 San Mateo, CA, United States· Full-time
✓ Quality checkedCompany trend -100%

Every day, tens of millions of people come to Roblox to explore, create, play, learn, and connect with friends in 3D immersive digital experiences– all created by our global community of developers and creators. At Roblox, we’re building the tools and platform that empower our community to bring any experience that they can imagine to life. Our vision is to reimagine the way people come together, from anywhere in the world, and on any device. We’re on a mission to connect a billion people with optimism and civility, and looking for amazing talent to help us get there. A career at Roblox means you’ll be working to shape the future of human interaction, solving unique technical challenges at scale, and helping to create safer, more civil shared experiences for everyone. The Luau App Foundations team is responsible for the core infrastructure of the Roblox application. They bridge the gap between app and the performance-heavy Roblox game engine. This team is building the unified stack that powers mission-critical surfaces like Home, Avatar, and Social for millions of concurrent users. They are the ones who make it possible for "Web-style" development efficiency to exist within a high-performance C++ game engine. Why is this role exciting: Technical Pioneer: You will be writing libraries and modules using C++ inside a world class Roblox proprietary Game Engine. Systematic Impact: This is a "Force Multiplier" role. The frameworks and components you build will be used by dozens of other engineering teams to ship their features. Complex Problem Solving: You aren’t just building an app; you’re managing smooth data flow through a client that has to perform perfectly on a $100 Android phone and a $3,000 Gaming PC simultaneously. 0 to 1 Transitions: You will lead the charge in shaping some of the most crucial components of the App written in C++ inside the Game Engine. Key Challenges: Bridging Tech Stacks: The libraries you write sit between a modern UI (written in

AWSGitRestAI
O
📍 San Francisco, California, United States· Full-time
✓ High-confidence listingCompany trend -82%

$295K – $380K/yr

Quick readStrong listing-quality and freshness signals

About the Team The OpenAI Robotics team is focused on unlocking general-purpose robotics and pushing towards AGI-level intelligence in dynamic, real-world settings. Working across the entire model stack, we integrate cutting-edge hardware and software to explore a broad range of robotic form factors. We strive to seamlessly blend high-level AI capabilities with the constraints of physical systems to improve peoples’ lives. About the Role As a Senior Software Engineer, ML Systems & Training Infrastructure, you will be a deeply hands-on engineering force multiplier for the robotics team. You will help keep the training framework and surrounding infrastructure healthy, review and improve code quickly, debug failures across ML systems and infrastructure, and unblock researchers and engineers when the path from idea to working training job gets rough. We’re looking for people who love writing, reading, reviewing, and fixing code; who can get productive quickly in unfamiliar systems; and who bring strong practical judgment without a lot of ego or process overhead. This role will be based in San Francisco, CA and be expected in office 5 days per week and offer relocation assistance to new employees. In this role, you will: Review, improve, and clean up code across training frameworks and adjacent infrastructure. Identify risky or low-quality changes before they land, and raise the code quality bar without slowing the team down. Debug issues across ML training systems, GPUs, clusters, networking, and related infrastructure. Help researchers and engineers unblock broken training jobs, flaky workflows, and brittle internal tooling. Improve the reliability, maintainability, and usability of the robotics team’s training framework. Move quickly on practical engineering problems that directly affect team velocity. You might thrive in this role if you: Have strong software engineering fundamentals and excellent code review judgment. Have experience with ML systems, training fr

AWSRestAIGo
O
📍 San Francisco, California, United States· Full-time
✓ Quality checkedCompany trend -82%

About the Team The OpenAI Robotics team is focused on unlocking general-purpose robotics and pushing towards AGI-level intelligence in dynamic, real-world settings. Working across the entire model stack, we integrate cutting-edge hardware and software to explore a broad range of robotic form factors. We strive to seamlessly blend high-level AI capabilities with the constraints of physical systems to improve peoples’ lives. About the Role As a Software Engineer, Distributed Data Systems, you will design, build, and operate some of the largest distributed data systems in the world. You will be responsible for the end-to-end stack to deliver and consume top-quality data for robotics training at exabyte-scale. You’ll manage distributed data pipelines, collaborate closely with researchers to translate requirements into robust systems, and harden pipelines that serve as the backbone for OpenAI’s rapid iteration cycles. We’re looking for engineers who are detail-oriented, have strong experience with distributed systems, and excel at building reliable, large-scale systems in high-stakes environments. This role is based in San Francisco, CA. We use a hybrid work model of 3 days in the office per week and offer relocation assistance to new employees. In this role, you will: Design, build, and maintain data infrastructure such as exabyte-scale distributed data processing, data selection, automated labeling, and training data loaders. Ensure our data platform can scale by orders of magnitude while remaining reliable and efficient. Partner with researchers to deeply understand requirements and translate them into production-ready systems. Harden, optimize, and maintain critical data infrastructure systems that power multimodal training and evaluation. Deliver the best possible data for training robotics models. You might thrive in this role if you: Have strong experience with distributed systems and large-scale infrastructure with a strong interest in data. Are detail-oriented a

AWSRestAIGo
O
📍 San Francisco, California, United States· Full-time
✓ Quality checkedCompany trend -82%

About the Team The OpenAI Robotics team is focused on unlocking general-purpose robotics and pushing towards AGI-level intelligence in dynamic, real-world settings. Working across the entire model stack, we integrate cutting-edge hardware and software to explore a broad range of robotic form factors. We strive to seamlessly blend high-level AI capabilities with the constraints of physical systems to improve peoples’ lives. About the Role As a Research Engineer, Distributed Data Systems, you will design and scale the infrastructure that powers large-scale multimodal training and evaluation at OpenAI. You’ll manage distributed data pipelines, collaborate closely with researchers to translate requirements into robust systems, and harden pipelines that serve as the backbone for OpenAI's rapid iteration cycles. We’re looking for engineers who are detail-oriented, have strong experience with distributed systems, and excel at building reliable infrastructure in high-stakes environments. This role is based in San Francisco, CA. We use a hybrid work model of 3 days in the office per week and offer relocation assistance to new employees. In this role, you will: Design, build, and maintain data infrastructure systems such as distributed compute, data orchestration, distributed storage, streaming infrastructure, machine learning infrastructure while ensuring scalability, reliability, and security. Ensure our data platform can scale by orders of magnitude while remaining reliable and efficient. Partner with researchers to deeply understand requirements and translate them into production-ready systems. Harden, optimize, and maintain critical data infrastructure systems that power multimodal training and evaluation. You might thrive in this role if you: Have strong experience with distributed systems and large-scale infrastructure with a strong interest in data. Are detail-oriented and bring rigor to building and maintaining reliable systems. Demonstrate excellent software enginee

AWSRestMachine LearningAI
O
📍 San Francisco, California, United States· Full-time
✓ High-confidence listingCompany trend -82%
Quick readStrong listing-quality and freshness signals

About the Team The Intelligence & Investigations Engineering team builds systems that detect, analyze, and disrupt abuse across OpenAI’s products. We partner closely with the Child Safety team and cross-functional groups to protect users while advancing OpenAI’s goal of developing AI that benefits everyone. About the Role As a Fullstack Engineer focused on child safety, you’ll build data-intensive, AI-powered applications and infrastructure that enable operators and investigators to work effectively and responsibly. You’ll adapt quickly in ambiguous, fast-moving environments to deliver well-crafted, reliable tooling for high-severity safety work. *Candidates should understand this role involves exposure to sensitive and egregious content. In this role, you will: 4+ years of experience as a software engineer Prototype, build, and maintain intelligence systems that detect, triage, and enable efficient human review of possible high severity harm Work hand in hand with operators and investigators, designing and delivering systems that enable them to do their work faster, more accurately, and more safely. Develop across the stack: UIs, services, pipelines, and anything else required to solve the problems we face. Interact with partners across Product Policy, Platform Integrity, Safety Systems, and Research Contribute to the team’s technical strategy, especially for child safety related tools and systems Report on impact in a data-driven fashion You might thrive in this role if you: Have a strong software engineering foundation and enjoy owning systems end-to-end—from infrastructure and data ingestion to frontend tooling Are energized by working at the frontier of AI capabilities, integrating new models and APIs into practical systems Have experience building and operating large-scale data pipelines or search/retrieval systems Are proficient in Python and/or TypeScript, and familiar with tools like Spark, Kafka, Flink, data warehouses, and SQL Take a product-minded ap

TypeScriptPythonSQLArtificial Intelligence
R
📍 San Mateo, CA, United States· Full-time
✓ High-confidence listingCompany trend -100%

From $295.3K/yr

Quick readStrong listing-quality and freshness signals

Every day, tens of millions of people come to Roblox to explore, create, play, learn, and connect with friends in 3D immersive digital experiences– all created by our global community of developers and creators. At Roblox, we’re building the tools and platform that empower our community to bring any experience that they can imagine to life. Our vision is to reimagine the way people come together, from anywhere in the world, and on any device. We’re on a mission to connect a billion people with optimism and civility, and looking for amazing talent to help us get there. A career at Roblox means you’ll be working to shape the future of human interaction, solving unique technical challenges at scale, and helping to create safer, more civil shared experiences for everyone. Engineering Manager, Home Infrastructure The Home Infrastructure team builds the mission-critical backend and data systems that power Roblox’s Homepage and Experience Details Page, two of the highest-traffic surfaces on Roblox. These surfaces reach the vast majority of Roblox’s daily active users and are core drivers of discovery, engagement, retention, and platform growth. We are a full-stack product infrastructure team responsible for content distribution across Roblox. Our systems support multiple modes of user interaction, including exploratory browsing, directed discovery, and personalized content recommendations across the many types of content that make up the Roblox ecosystem. This team sits at the intersection of large-scale distributed systems, machine learning-powered personalization, data infrastructure, and product experimentation. We partner closely with Machine Learning, Data Science, Product, Design, Frontend, Ads, Marketplace, Virtual Economy, and other teams across Roblox to build the platforms that help users find the most relevant and engaging content. As Engineering Manager for Home Infrastructure, you will lead a team of Backend and Data Engineers responsible for the e

AWSGitMachine LearningAI
P
📍 United States· Full-time
✓ High-confidence listingCompany trend -86.3%

From $285.5K/yr

Quick readStrong listing-quality and freshness signals

About Pinterest: Millions of people around the world come to our platform to find creative ideas, dream about new possibilities and plan for memories that will last a lifetime. At Pinterest, we’re on a mission to bring everyone the inspiration to create a life they love, and that starts with the people behind the product. Discover a career where you ignite innovation for millions, transform passion into growth opportunities, celebrate each other’s unique experiences and embrace the flexibility to do your best work. Creating a career you love? It’s Possible. At Pinterest, AI isn't just a feature, it's a powerful partner that augments our creativity and amplifies our impact, and we’re looking for candidates who are excited to be a part of that. To get a complete picture of your experience and abilities, we’ll explore your foundational skills and how you collaborate with AI. Through our interview process, what matters most is that you can always explain your approach, showing us not just what you know, but how you think. You can read more about our AI interview philosophy and how we use AI in our recruiting process here . As a principal engineer on the Online Systems team, you’ll join a team that powers Pinterest’s most business-critical online systems at massive scale, driving the reliability, efficiency, and evolution behind every core Pinner and Advertiser experience. You'll lead major efforts like multi-region deployment and Kubernetes migration, set the standard for operational excellence, and define the long-term vision for our online serving infrastructure, supporting machine learning and product innovation across the company. This is an opportunity for high-impact technical leadership, broad visibility, and cross-functional influence at the heart of Pinterest’s platform. What you’ll do: Improve reliability, scalability and infra efficiency for Pinterest’s critical online systems across storage and caching, online service and realtime analytics syste

PythonJavaAWSKubernetes
R
📍 San Mateo, CA, United States· Full-time
✓ High-confidence listingCompany trend -100%

From $195.8K/yr

Quick readStrong listing-quality and freshness signals

Every day, tens of millions of people come to Roblox to explore, create, play, learn, and connect with friends in 3D immersive digital experiences– all created by our global community of developers and creators. At Roblox, we’re building the tools and platform that empower our community to bring any experience that they can imagine to life. Our vision is to reimagine the way people come together, from anywhere in the world, and on any device. We’re on a mission to connect a billion people with optimism and civility, and looking for amazing talent to help us get there. A career at Roblox means you’ll be working to shape the future of human interaction, solving unique technical challenges at scale, and helping to create safer, more civil shared experiences for everyone. Recommendation Systems are a key growth lever at Roblox, driving retention, engagement, and monetization for hundreds of millions of users. This role offers the unique opportunity to redefine how users search and discover everything from the most interesting immersive experiences and digital avatars in our Marketplace to personalized advertising. You will solve a diverse range of high-scale ranking, retrieval, and personalization problems across our platform. We combine cutting-edge research —including deep learning, generative AI, and reinforcement learning techniques— with large-scale engineering to bridge experimentation and production; you'll design algorithms that operate at massive scale and shape the next generation of recommender systems for user-generated content. Teams Hiring for This Role Search and Discovery: powers major recommendation surfaces—conducting cutting-edge research in generative modeling, multimodal and MLLM technologies, designing advanced agentic AI algorithms to solve business requirements while achieving technical breakthroughs. Safety, Alt Defense: architects a massive-scale detection engine that identifies recidivist bad actors across billions of account

PythonJavaAWSGit
M
📍 Boise, ID - Main Site, United States
✓ Quality checkedCompany trend -75%

Our vision is to transform how the world uses information to enrich life for all . Micron Technology is a world leader in innovating memory and storage solutions that accelerate the transformation of information into intelligence, inspiring the world to learn, communicate and advance faster than ever. The AI Engineer, People Technology is responsible for designing, developing, and deploying AI-powered solutions that transform work across the People Organization. This role combines software engineering, AI development, and HR domain expertise to build intelligent applications, automations, and agents that improve employee experiences, increase operational efficiency, and accelerate workforce transformation. The ideal candidate is a hands-on builder with demonstrated experience using AI Assisted Software Development Platforms to develop enterprise AI solutions. You must have successfully designed and deployed AI agents that collaborate across multiple platforms, systems, and business functions while operating within enterprise governance, security, and compliance standards. This role requires deep knowledge of HR technologies, including Workday, ServiceNow, and the Microsoft Copilot ecosystem, along with a passion for applying AI to solve complex business challenges. Responsibilities: AI Product & Solution Development: Experience with the end-to-end product lifecycle turning a vision into a roadmap while driving adoption and value delivery. Design, develop, test, and deploy AI-powered products, applications, and intelligent workflow solutions. Apply AI Assisted Development Tools to accelerate software development, solution building, and deployment activities. Support authorities in translating business needs into developed solutions and prototypes. Develop reusable frameworks, ser

PythonAzureDockerMachine Learning
R
📍 New York City, NY, United States· Full-time
✓ High-confidence listingCompany trend -99.2%

From $10K/yr

Quick readStrong listing-quality and freshness signals

About Ramp Ramp is building the smart infrastructure for finance teams, embedded in the transaction flow of every dollar a business spends. We automate how over $200B in annualized spend flows in and out of 70,000+ companies: authorizing payments, flagging risk, categorizing spend, and closing books. The problems are high-stakes, data-dense, and unforgiving. We hire people with high agency and high urgency. We look for slope over intercept. We care less about where you trained and more about what you’ve built. At Ramp, everyone is a builder who owns problems end to end and makes consequential decisions that shape the outcome. The median Ramp customer saves 5% and grows revenue 16% in their first year – far in excess of businesses operating without Ramp. We believe every ambitious company deserves the same. If you want to build systems that directly shape how companies move and manage billions, Ramp is the place to do it. About the Role The Financial Intelligence team, part of Ramp's Applied AI org, powers the agentic analysis, FP&A, and book-close experiences that over 70,000 businesses rely on to run their finances. We turn messy financial data into a fast, trustworthy, governed data layer that AI agents can work with and build artifacts on top of. This is a frontend-leaning role for an engineer who obsesses over interaction design and data-dense UX, but is just as comfortable designing the API that feeds it. You'll own the surfaces customers actually touch: agentic financial analysis, month-end close, and exploratory data experiences that feel as polished as the best business intelligence tools. If you want your frontend work to sit at the center of real production LLM systems rather than being bolted on at the end, this is the role. What You’ll Do Design and ship customer-facing AI experiences end to end, from React UI through to the APIs and data contracts behind them Build BI-tool-quality interfaces for agentic analysis, FP&A, and book-close workflows:

TypeScriptReactRestAI
R
📍 New York City, NY, United States· Full-time
✓ High-confidence listingCompany trend -99.2%

From $10K/yr

Quick readStrong listing-quality and freshness signals

About Ramp Ramp is building the smart infrastructure for finance teams, embedded in the transaction flow of every dollar a business spends. We automate how over $200B in annualized spend flows in and out of 70,000+ companies: authorizing payments, flagging risk, categorizing spend, and closing books. The problems are high-stakes, data-dense, and unforgiving. We hire people with high agency and high urgency. We look for slope over intercept. We care less about where you trained and more about what you’ve built. At Ramp, everyone is a builder who owns problems end to end and makes consequential decisions that shape the outcome. The median Ramp customer saves 5% and grows revenue 16% in their first year – far in excess of businesses operating without Ramp. We believe every ambitious company deserves the same. If you want to build systems that directly shape how companies move and manage billions, Ramp is the place to do it. About the Role As a software engineer on the AI Soltuions team, you will co-lead customer engagements with an AI Solutions Strategist . The Strategist owns business discovery, ROI narrative, stakeholder alignment, and rollout planning. The engineer owns technical discovery, solution design, prototyping, implementation, and production readiness. This is a deeply client-facing role. You will spend significant time with customers and end users, moving projects from bootcamp and workflow discovery through implementation, launch, and steady production usage. What You’ll Do Translate customer goals into clear system requirements and non-functional requirements covering security, privacy, reliability, performance, scalability, and cost. Partner directly with customers to understand current workflows, constraints, systems, data quality, and adoption blockers. Create and maintain solution architecture artifacts: System context and data flow diagrams Integration plan across Ramp and customer systems Security model covering permissions, access patterns, and au

JavaScriptTypeScriptPythonJava
P
📍 San Francisco, California, United States· Full-time
✓ Quality checkedCompany trend -72.3%

We believe that the way people interact with their finances will drastically improve in the next few years. We’re dedicated to empowering this transformation by building the tools and experiences that thousands of developers use to create their own products. Plaid powers the tools millions of people rely on to live a healthier financial life. We work with thousands of companies like Venmo, SoFi, several of the Fortune 500, and many of the largest banks to make it easy for people to connect their financial accounts to the apps and services they want to use. Plaid’s network covers 12,000 financial institutions across the US, Canada, UK and Europe. Founded in 2013, the company is headquartered in San Francisco with offices in New York, Washington D.C., London and Amsterdam. Team: Plaid is becoming an AI-first company, and Intelligent Tooling builds internal platforms and tools to lead the transformation. Our biggest opportunity isn't just better tools for engineers, it's extending AI-native internal tooling to the rest of Plaid. Tools built for engineers assume things non-engineers don't have: local toolchains, monorepos, engineer credentials, PR-based workflows. That mismatch means Ops, Support, and other teams can't easily inherit what we build for engineering. They need their own path and we're building that path. Role: As a Senior Software Engineer on Intelligent Tooling, you will build and operate internal systems that empower non engineering teams to automate their workflows with AI. You will own the product and platform layer for internal tools, including the constraints and infrastructure that keep those tools safe and maintainable. There's no existing playbook for this at Plaid. You will define what the right non-eng AI surface looks like, ship its first durable versions, and partner closely with internal users to make sure it solves real problems. You will act as the engineering point of contact embedded with non-engineering teams, running discovery and trans

O
📍 San Francisco, California, United States· Full-time
✓ High-confidence listingCompany trend -82%
Quick readStrong listing-quality and freshness signals

About the Team The Monetization team is a new cross-functional group working across engineering, product, research, and design to build the foundational systems that will help OpenAI scale access to intelligence responsibly. Our mission is to develop user-first, privacy-preserving monetization products—including next-generation ads experiences—that strengthen user trust, unlock economic opportunity, and support OpenAI’s long-term innovation. Monetization plays a critical role in enabling OpenAI to continue pushing the boundaries of AI capabilities while ensuring the benefits of AGI are broadly shared. We believe monetization must be aligned with user value, uphold rigorous privacy and safety standards, and sustain a healthy ecosystem of developers and businesses. This team operates in a greenfield environment and moves quickly through prototyping, experimentation, and iterative deployment. We partner closely with Product, Design, and Research to bring research breakthroughs into real-world systems at global scale. About the Role As a Research Engineer in OpenAI's Monetization Group, you will have the opportunity to work with some of the brightest minds in AI. You'll contribute to deploying state-of-the-art models in production environments, helping turn research breakthroughs into tangible solutions. If you're excited about making AI technology accessible and impactful, this role is your chance to make a significant mark. In this role, you will: Innovate and Deploy: Design and deploy advanced machine learning models that solve real-world problems. Bring OpenAI's research from concept to implementation, creating AI-driven applications with a direct impact. Collaborate with the Best: Work closely with researchers, software engineers, and product managers to understand complex business challenges and deliver AI-powered solutions. Be part of a dynamic team where ideas flow freely and creativity thrives. Optimize and Scale: Implement scalable data pipelines, optimize mod

Machine LearningArtificial IntelligenceAI
C
📍 United States· Full-time
✓ Quality checkedCompany trend -100%

At ClickUp, we're building the future of work: the first truly converged AI workspace unifying tasks, docs, chat, calendar, and enterprise search, all supercharged by context-driven AI. We are an AI-native company. Every team member is expected to leverage AI daily, and we evaluate AI fluency as part of our hiring process. Join us and help redefine what's possible. 🚀 Role Overview: We are seeking a skilled and experienced Senior AI Engineer – AI Platform to join our ClickUp Engineering team. In this role, you will play a critical part in both building the core AI platform and directly applying large language models (LLMs) to deliver intelligent features across ClickUp. You will focus on backend systems that enable scalable, reliable, and secure AI-powered capabilities, while also working hands-on with LLMs to solve real user problems and drive product innovation. Key Responsibilities: Architect, design, and implement scalable AI platform services that support the deployment, orchestration, and lifecycle management of LLMs and other AI models. Apply LLMs and other AI technologies directly to build and enhance ClickUp’s intelligent features, working closely with product and engineering teams to deliver impactful solutions. Build and maintain robust APIs and backend systems that enable seamless integration of AI-powered features into ClickUp’s core platform. Develop infrastructure for model serving, monitoring, logging, and automated evaluation to ensure high reliability and performance of AI services in production. Integrate with multiple LLM providers (e.g., OpenAI, Anthropic, Google) and manage model selection, routing, and fallback strategies for optimal performance and cost. Drive the adoption of best practices in AI privacy, security, and compliance, including data anonymization, secure data handling, and regulatory adherence. Optimize platform performance, scalability, and cost-efficiency, leveraging cloud-native technologies and distributed systems. Stay curre

TypeScriptPythonAWSAzure
🔔

Get new ai systems engineer jobs in United States by email

Daily job updates · Unsubscribe anytime