Anthropic appears poised to release Claude Sonnet 5 imminently, according to multiple reports circulating in early February 2026. Developer forums and cloud service logs show references to a new model build labeled Claude Sonnet 5 with an internal date string of February 3, suggesting preparation for public rollout.
Leaked identifiers point to an internal codename "Fennec" appearing in Google Vertex AI logs, confirming the model exists in Anthropic's development pipeline. The timing aligns with industry speculation that Anthropic could launch during Super Bowl week, though the company has not confirmed any release date.
Performance benchmarks circulating in developer communities suggest Sonnet 5 could score above 80.9% on SWE-Bench, potentially matching or surpassing Claude Opus 4.5 in coding tasks, according to unverified leaks.
Early testing reportedly shows the model outperforming Opus 4.5 in some workflows, particularly for UI-focused and rendering-related coding, according to unverified leaks.
Pricing rumors suggest Sonnet 5 could cost significantly less than Claude Opus 4.5 while delivering comparable or superior performance, though specific pricing remains unconfirmed.
Technical specifications under discussion include a potentially larger context window, with some sources suggesting it could reach one million tokens, though this remains speculative.
Infrastructure optimizations may include Google TPU compatibility, enabling higher throughput and reduced latency.
A 403 Forbidden error on a specific Sonnet 5 Vertex ID suggests the model already exists internally and awaits activation on Google's cloud platform.
(A fabricated model ID like claude-sonnet-99 returns a 404 Not Found, indicating the resource doesn't exist at all.)
The model reportedly demonstrates strong math capabilities and structured visual generation, with testers noting unusually complete output for ASCII world map prompts. These improvements align with Anthropic's focus on agent-style capabilities and complex reasoning tasks.
Sonnet 5's positioning between the lighter Haiku line and premium Opus models suggests Anthropic aims to close performance gaps while maintaining cost efficiency. This strategy addresses developer and enterprise needs for capable AI tools that remain economically viable at scale.
Industry analysts note that internal artifacts frequently leak ahead of official announcements, creating speculation cycles that sometimes outpace actual development timelines. While the "Fennec" log entry confirms internal testing, specific performance claims and release dates remain unverified.
The AI competitive landscape continues intensifying as OpenAI removes older ChatGPT models and Google advances Gemini development.
Anthropic's potential Sonnet 5 release represents another move in the ongoing battle for developer mindshare and enterprise adoption.
Until Anthropic provides official confirmation, the community relies on cloud log sightings and developer forum discussions to gauge Sonnet 5's capabilities. The combination of performance improvements and cost reductions, if realized, could significantly impact how organizations deploy AI for coding and complex workflows.
