Anthropic debuts Claude Sonnet 4.5: long-horizon autonomous coding, benchmark wins, and a new Agent SDK

Anthropic’s announcement of Claude Sonnet 4.5 on September 29, 2025 marks an inflection point in how we think about “coding models.” Rather than chasing single-prompt benchmark highs, Sonnet 4.5 is explicitly engineered for durable autonomy: multi-stage, day-long agentic workflows that plan, act, iterate, and deliver production-quality software with minimal human oversight. Available immediately via the Claude API and the Claude chatbot at the same price as Sonnet 4 ($3 per million input tokens, $15 per million output tokens), Sonnet 4.5 pairs performance claims on conventional benchmarks with a new emphasis on long horizons and safety for agents that touch real infrastructure. What’s new and why it matters Anthropic positions Sonnet 4.5 as its most capable frontier model for coding and “computer use” to date. Public coverage emphasizes two linked themes: benchmark wins and long-horizon autonomy. On paper, Anthropic reports leading results on coding evaluations including SWE-Bench Verified; more importantly for practical engineering, the company argues that traditional leaderboards understate models’ abilities on extended, interdependent workflows. Internal trials cited by TechCrunch and independent reporting from outlets like The Verge describe Sonnet 4.5 autonomously carrying out up to 30-hour sessions. In those sessions the agent didn’t merely generate snippets: it stood up databases, provisioned cloud resources, purchased domains, ran integration tests, and even completed procedural compliance tasks akin to parts of a SOC 2 audit. This capability stack—planning, tool orchestration, iterative debugging, and secure handling of credentials—matters because shipping real software is not an isolated test-case. It is a sequence of dependent tasks that often spans days. Anthropic’s thesis is that winner-take-most market share in developer tools will go to models that can sustain work across those longer horizons rather than models optimized for single-turn accuracy. Positioning against rivals The release lands amid renewed competition from OpenAI’s GPT-5 and other frontier models. TechCrunch frames the Sonnet 4.5 story as a response to the benchmarking arms race, with Anthropic arguing that while rivals post impressive point-in-time scores, Sonnet 4.5 leads in scenarios where agents must plan, execute, and iterate over many hours. Axios and others highlight the shift from the roughly seven-hour autonomy horizon in earlier frontier models to the day-long horizons demonstrated in Anthropic’s trials. Practically, that could change how engineering teams allocate tasks: from treating LLMs as coding copilots to treating them as automated members of the delivery pipeline. Developer validation and tooling Validation from partners matters. CEOs of Cursor and Windsurf, two AI-first IDEs, told TechCrunch that Sonnet 4.5 represents a leap on longer-horizon coding tasks—better reliability across planning → implementation → refinement loops, not just point-in-time completions. To enable that kind of agentic behavior for external developers, Anthropic also launched the Claude Agent SDK. The SDK exposes the same multi-tool orchestration stack that powers Claude Code, allowing teams to build custom agents that combine browsing, shell access, cloud provisioning, and third-party APIs. For organizations experimenting with autonomous agents that must interact with repositories, CI/CD, and cloud accounts, this infrastructure is the missing piece. Imagine with Claude, a research preview for Max subscribers, demonstrates real-time, on-the-fly software generation—another signal that Anthropic is leaning into fluid, interactive agent experiences that evolve during long sessions. Safety and alignment for long sessions One of the central risks with agents that touch secrets, repos, and cloud resources is safety. Anthropic explicitly markets Sonnet 4.5 as its most aligned frontier model to date, with improvements in resistance to prompt injection, lower tendencies toward sycophancy and deceptive behavior, and generally tighter constraints around dangerous or unauthorized operations. TechCrunch highlights these upgrades alongside the coding gains; in practice, enterprises will need to vet these claims through penetration testing and red-team evaluations before allowing long-running agents to act on production environments. Pricing and availability Sonnet 4.5 is available now in Claude’s web and mobile chat and via the Claude API with the same token pricing as Sonnet 4—$3 per million input tokens and $15 per million output tokens. The lack of a price increase is notable: Anthropic appears to be removing cost friction for teams that want to trial longer-horizon workflows and to compete with incumbents on both performance and practical economics. What this means for Morocco’s AI ecosystem For Morocco, Sonnet 4.5 and the Agent SDK could be particularly consequential across government, startups, and industry. - Government modernization and digital services: Morocco’s public sector has invested in e-governance and digital ID initiatives in recent years. Long-horizon agents could automate end-to-end development of citizen-facing portals, from requirements and architecture to deployment and compliance checks. With Sonnet 4.5’s reported ability to handle multi-stage tasks, Moroccan ministries could accelerate prototyping and productionization of services while using the SDK to enforce auditability and data sovereignty controls locally. - Startups and SaaS builders: Casablanca and Rabat’s growing startup scenes—spanning fintech, healthtech, agritech, and e-commerce—stand to benefit from agents that can reduce time-to-market. A Moroccan fintech startup could task an agent to scaffold backend services, wire up payments integrations, and run security checks in a single long-running session. For early-stage teams with limited engineering bandwidth, Sonnet 4.5 may compress months of work into a set of confirmable agent-driven runs, provided that security and compliance are validated. - Agritech and localization: Agents that can persist across longer workflows are useful for domain-specific applications like downstream agritech solutions that require integrations with sensor networks, analytics pipelines, and user-facing mobile apps in French and Arabic. The Agent SDK could speed the development of localized interfaces and data-processing pipelines that respect regional data rules and linguistic needs. - Talent development and education: Morocco’s universities and coding bootcamps can incorporate long-horizon agent use into curricula to teach software engineering workflows that align with industry. Students could learn how agents plan across multiple development stages and how to set up guardrails for security and compliance—skills that will be in demand if teams adopt Sonnet-style autonomous agents. Challenges and considerations for Moroccan adopters - Data sovereignty and cloud locality: Moroccan organizations will need to evaluate where inference and data processing occur. Even with the SDK, enterprises will likely demand on-prem or regionally hosted inference options and strict controls over credential handling. - Regulatory and compliance landscapes: As agents gain permission to act autonomously, regulatory frameworks in Morocco and the MENA region will need to address liability, auditing, and certification of AI-driven software delivery—especially for sectors like finance and healthcare. - Integration with local ecosystems: To extract practical value, Sonnet-powered agents must integrate with local payment providers, telecom operators, and government APIs. The SDK lowers the bar, but success still requires engineering effort to connect tools and enforce local policies. The bottom line Anthropic’s Sonnet 4.5 reframes the conversation from isolated benchmark gains to the engineering reality of shipping software. For Morocco, the combination of long-horizon reasoning, an Agent SDK, and an unchanged pricing model lowers technical and economic barriers to experimentation by governments, startups, and educational institutions. The crucial next steps for Moroccan adopters are to pilot Sonnet 4.5 in controlled environments, validate safety and compliance claims, and invest in integrations that respect data sovereignty and local regulations. If Anthropic’s 30-hour demos generalize beyond hand-picked examples, Sonnet 4.5 could change what teams expect from coding models—transforming them from assistive copilots into autonomous contributors within the Moroccan tech stack.