The First AI to Break 82% SWE-bench
Codename Fennec | Released February 3, 2026 | By Anthropic
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Claude Sonnet 5, internally codenamed "Fennec", is Anthropic's latest mid-tier flagship model released on February 3, 2026. It represents a generational leap in AI software engineering capabilities.
Built for "Agentic Autonomy", Claude Sonnet 5 is optimized for Google's Antigravity TPU infrastructure, utilizing a "distilled reasoning" architecture that compresses the power of a flagship model into a highly efficient inference engine. It outperforms the more expensive Claude Opus 4.5 in coding benchmarks while maintaining aggressive pricing.
How the AI community predicted the February 3, 2026 release before the official announcement.
Developers spot mysterious model ID claude-sonnet-5@20260203 appearing in Google Vertex AI backend logs.
SWE-bench scores of 82.1% circulate on X (formerly Twitter) and Reddit communities r/ClaudeAI and r/google_antigravity.
Reports emerge of "Antigravity" environment updates rolling out to Pro users on Google Cloud.
Claude Sonnet 5 launches simultaneously across Anthropic API, Amazon Bedrock, and Google Vertex AI.
Breaking the 80% barrier represents a fundamental shift from AI as "copilot" to AI as "autonomous engineer."
At 82%, Sonnet 5 can take a raw bug report and independently write, test, and verify a patch that fixes the issue on the first try—matching junior developer performance.
Higher accuracy means senior developers spend significantly less time fixing "hallucinated" code. The coding-to-review ratio shifts from 1:1 to 1:10.
Unlike previous models, Sonnet 5 can understand how a change in a React frontend component might affect a Go-based microservice in the same repository.
Claude Sonnet 5 introduces groundbreaking capabilities that redefine AI-assisted software development.
Capable of taking raw bug reports and independently writing, testing, and verifying patches that fix issues on the first try. Achieves junior-developer parity.
Process massive codebases with the same latency Sonnet 3.5 processed 200K. Features "warm" context that persists across multiple days without re-parsing.
Multi-Agent Orchestrator that spawns specialized sub-agents for Backend, QA, and Infrastructure. Agents work simultaneously on different files with automatic conflict resolution.
Hybrid reasoning model supporting both standard responses and step-by-step deep thinking for complex tasks. Fine-grained control over thinking duration via API.
Reliably handles browser-based tasks from competitive analysis to procurement workflows. Navigate sites, fill spreadsheets, and complete tasks autonomously.
Compressed flagship intelligence into an efficient inference engine. Speculative decoding on TPU hardware enables parallel token prediction for instant-feeling responses.
Anthropic partnered with Google to optimize Sonnet 5 for the Antigravity layer—a high-performance compute environment built on TPUv6 architecture.
Sonnet 5 processes 1 million context tokens with the same latency that Sonnet 3.5 processed 200K. This 5x improvement enables real-time analysis of entire enterprise codebases.
The Antigravity layer enables "warm" context—your entire 1M token codebase persists across multiple days without re-parsing for every message. Resume complex tasks instantly.
Specialized TPU hardware allows the model to predict 10-20 tokens in parallel, resulting in a typing speed that feels instantaneous to users.
The standout feature of Sonnet 5 is its ability to operate as a Multi-Agent Orchestrator through the Claude Code CLI.
Sonnet 5 analyzes your high-level goal and creates an execution plan, identifying which components need modification.
Specialized sub-agents are spawned: one for Backend, one for QA (Quality Assurance), and one for Infrastructure.
Agents work simultaneously on different files. While the Backend agent writes a new API route, the QA agent generates unit tests for it.
If agents propose conflicting changes, the Manager agent reconciles the logic before presenting the final PR to you.
Compare Claude Sonnet 5 against previous versions and competing models to understand the performance leap.
| Specification | Claude Sonnet 5 | Claude Sonnet 4.5 | Gemini Snow Bunny | OpenAI Codex 5.3 |
|---|---|---|---|---|
| Release Date | Feb 3, 2026 | Sep 29, 2025 | Q4 2025 | Q1 2026 |
| SWE-bench Score | 82.1% ⭐ | 77.2% / 82.0%* | 76.4% | 79.8% |
| Context Window | 1M tokens | 200K / 1M (beta) | 2M tokens | 128K tokens |
| Input Price (per 1M) | $3.00 | $3.00 | $4.50 | $4.00 |
| Output Price (per 1M) | $15.00 | $15.00 | $12.00 | $16.00 |
| Max Output | 64K tokens | 64K tokens | 32K tokens | 32K tokens |
| Primary Advantage | Agentic Autonomy | Hybrid Reasoning | Multimodal Search | Inline Speed |
| Multi-Agent Mode | ✅ Dev Team | ❌ | ❌ | ❌ |
* Sonnet 4.5 achieves 82.0% with high compute configuration using parallel sampling and rejection sampling.
Flagship intelligence at disruptive pricing. 50% cheaper than Opus 4.5 while outperforming it.
By pricing Sonnet 5 at $3 per million tokens, Anthropic has made "flagship intelligence" affordable for mass automation.
Developers are moving away from trial-and-error prompting toward rigorous "System Orchestration" where AI handles implementation details.
With AI handling 80% of implementation, the human role is shifting toward System Architect and Product Designer responsibilities.
Small teams can deploy "Agentic Staff" that handle maintenance and bug fixing for less than a single junior developer's monthly salary.
Anthropic has built its reputation on Safety and Constitutional AI. Sonnet 5 reflects this expertise.
Unlike models that blindly follow prompts into security vulnerabilities, Sonnet 5 is trained to identify and warn users about potential risks like SQL injections or cross-site scripting (XSS) in generated code.
The 82.1% SWE-bench score is not just a marketing number—it has been verified by independent testing firms like Vals AI, ensuring reliability for production environments.
Sonnet 5 is Anthropic's most aligned model yet, showing improvements across deception, sycophancy, power-seeking behaviors, and prompt injection defense.
Claude Sonnet 5 is available across multiple platforms. Use the model ID to integrate with your preferred service.
claude-sonnet-5@20260203
Claude Sonnet 5 was officially released on February 3, 2026. The release was preceded by leaks in late January 2026 when developers first spotted the model ID claude-sonnet-5@20260203 appearing in Google Vertex AI error logs. The model was codenamed "Fennec" internally.
Claude Sonnet 5 achieved an 82.1% score on SWE-bench, making it the first AI model to break the 80% barrier. This represents a significant leap over Claude Opus 4.5's 78.9% and demonstrates junior-developer level parity in resolving real GitHub issues.
Sonnet 5 actually outperforms the more expensive Opus 4.5 in coding benchmarks (82.1% vs 78.9% on SWE-bench). It offers the same $3/$15 pricing as Sonnet 4.5 while providing flagship-level intelligence, making it effectively a 50% price reduction for top-tier performance.
Antigravity refers to a high-performance compute environment on Google Cloud built on TPUv6 architecture. It enables Sonnet 5 to process 1M context tokens with the same latency that Sonnet 3.5 processed 200K. It also supports "warm" context persistence across multiple days and speculative decoding for instant-feeling responses.
Dev Team Mode is a Multi-Agent Orchestrator feature in Sonnet 5. When triggered via Claude Code CLI, Sonnet 5 spawns specialized sub-agents (Backend, QA, Infrastructure) that work simultaneously on different files. A Manager Agent reconciles any conflicts before presenting the final result.
Migration is straightforward—simply update the model parameter from claude-sonnet-4-5-20250929 to claude-sonnet-5-20260203. We recommend testing in a staging environment first, running your full test suite for structured outputs and tool calling, then gradually routing production traffic to Sonnet 5 while monitoring quality metrics.