StepFun: Step 3.5 Flash

Generates text by selectively activating only 11B of 196B parameters per token using a sparse Mixture of Experts (MoE) architecture. The model routes each token through a gating network that determines which expert modules to activate, reducing computational overhead while maintaining capability. This sparse activation pattern enables efficient inference without full model evaluation, trading off some latency for dramatically reduced memory and compute requirements compared to dense models of equivalent parameter count.

Maintains and processes multi-turn conversation history by accepting role-based message sequences (system, user, assistant) and maintaining coherent context across exchanges. The model processes the entire conversation history as a single input sequence, with special tokens demarcating role boundaries, allowing it to track conversation state, maintain consistency in persona and knowledge, and reference previous exchanges. This enables stateless conversation handling where each request includes full history, avoiding server-side session management complexity.

Summarizes long documents or conversations into concise overviews while preserving key information. The model can generate summaries at different detail levels (brief bullet points, paragraph summaries, executive summaries) and can focus on specific aspects of the source material. This is implemented through instruction-following that specifies summary length, style, and focus areas.

Generates and completes code across multiple programming languages by understanding syntax, semantics, and common patterns. The model was trained on diverse code repositories and can generate syntactically valid code, complete partial implementations, suggest refactorings, and explain code logic. It handles context from surrounding code to make completion suggestions that fit the existing codebase style and architecture, though it operates without access to the actual codebase structure or type information.

Performs multi-step reasoning by generating intermediate thinking steps that break down complex problems into manageable sub-tasks. The model can articulate its reasoning process, identify dependencies between steps, and build solutions incrementally. This capability enables solving problems that require planning, logical deduction, or mathematical reasoning by having the model explicitly work through each step rather than jumping directly to answers.

Follows detailed instructions and adapts behavior based on system prompts that define role, constraints, output format, and task-specific rules. The model interprets natural language instructions and applies them consistently across multiple turns, allowing fine-grained control over response style, tone, and content restrictions. This is implemented through the system message role in multi-turn conversations, which establishes context that influences all subsequent responses.

Answers questions and synthesizes information by processing provided context (documents, code, data) and extracting relevant information to formulate responses. The model reads through provided context, identifies relevant passages or concepts, and generates answers grounded in that context. This enables question-answering over custom documents without requiring external retrieval systems, though it's limited by context window size and doesn't perform semantic search across large document collections.

Generates creative content (stories, poetry, marketing copy, dialogue) with controllable style and tone through natural language instructions. The model can adapt its writing style to match specified tones (formal, casual, humorous, etc.), genres, and audience levels. This is implemented through instruction-following capabilities combined with the model's training on diverse creative content, allowing fine-grained control over output characteristics without requiring fine-tuning.

Provides inference access through OpenRouter's API, supporting both streaming responses (token-by-token output) and batch processing modes. Streaming enables real-time response display and lower perceived latency, while batch processing allows efficient processing of multiple requests. The API handles load balancing, rate limiting, and infrastructure management, abstracting away the complexity of running the sparse MoE model directly.

Extracts structured information from unstructured text and generates valid JSON output by understanding schema requirements and formatting constraints. The model can parse natural language descriptions, identify relevant entities and relationships, and output them in specified JSON structures. This enables programmatic processing of model outputs without requiring post-hoc parsing or validation.

Translates text between multiple languages and generates content in non-English languages with appropriate grammar, idioms, and cultural context. The model understands linguistic nuances and can maintain meaning and tone across language boundaries. This capability extends to code comments, technical documentation, and creative content in multiple languages.